This article was downloaded by: 10.3.98.104 On: 28 Sep 2021 Access details: subscription number Publisher: CRC Press Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: 5 Howick Place, London SW1P 1WG, UK
Laser Beam Shaping Applications
Fred M. Dickey, Todd E. Lizotte
Laser Beam Shaping in Array-Type Laser Printing Systems
Publication details https://www.routledgehandbooks.com/doi/10.1201/9781315371306-4 Andrew F. Kurtz, Daniel D. Haas, Nissim Pilossof Published online on: 01 Mar 2017
How to cite :- Andrew F. Kurtz, Daniel D. Haas, Nissim Pilossof. 01 Mar 2017, Laser Beam Shaping in Array-Type Laser Printing Systems from: Laser Beam Shaping Applications CRC Press Accessed on: 28 Sep 2021 https://www.routledgehandbooks.com/doi/10.1201/9781315371306-4
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3.5.2 3.5.1 3.4.1 3.7.3 3.7.2 3.6.1 3.5.3 3.4.4 3.5.5 3.7.5 3.7.4 Systems Modulator Array and Array Laser Printing Laser Subarray Modulated Systems Media to Laser Direct 3.4.3 3.4.2 Optics Cross-Array and Array 3.3.2 Characteristics Source Laser 3.2.4 3.2.3 Interaction Print-Head/Media Introduction 3.2.2 3.2.1 3.3.1 3.5.4 3.3.3 3.7.1 3
Alternate Array Print-Head Designs Print-Head Array Alternate Homogenizer Bar Integrating an with Print-Head Array An aFly’s with Print-Head Array An Eye Integrator Light Modulators Spatial System Modulator Array XeroxThe TIR Print-Head of a Monolithic Configuration Multichannel Optical Arrays Addressable with Laser Print-Head Fiber Array Print-Head Fiber Array Systems Optical Laser Discrete with Printing Array Optics Free-Space via Mapped Multiple Lasers Discrete Media the to Mapped Emitters Laser Issues Alignment Optical Smile of Laser Dependence Operating Correction Smile Laser Error Smile Laser Sources Laser Other Light as Sources Arrays Laser Shape Issues...... Beam and Coherence Laser Size, Profile Shape, and Interaction—Spot Laser/Media Print-Heads Interaction—Multisource Laser/Media of Focus Interaction—Depth Laser/Media Media Thermal Laser and Nissim Pilossof Nissim and Andrew F. Kurtz, Daniel D Systems Printing in Array-Type Laser Shaping Beam Laser ...... H ...... aas ...... 100 104 108 64 60 66 99 97 80 92 96 87 93 93 69 77 89 63 83 79 72 70 58 57 78 76 75 81 81 61 Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 3.8 in a direction parallel to the axis of rotation of the drum. For example, laser thermal For example, laser thermal of drum. of rotation the axis the to parallel adirection in (fast amultitude (12–250) is achieved scan) by translating printing beams of writing scan r/min), line and which holds media, the (at up 3000–4000 to speeds adrum ing the page scan where lathes, like (slow configured scan) rotat by motion is obtained are printers These spots. writing intoof series a light configured emitted the with high-power use one or more typically designs lasers, Efficientprinter required. are design approaches optical other encountered, resolution, insensitive an are and media high- for high-throughput, of requirements applications, trinity whenthroughput the (2D) image. may moved (slow be page scan the in atwo-dimensional create to scan) direction media the (fast of data, image scan a line swept produce to line scan) the in direction (AOM). modulator device acousto-optic such an external as spot isan laser the As via laser the to may either applied directly be density of pixel spot, each by correct pixel. modulation the The create to means, spot or pixel (the element),a written image smallest input by as some modulation objective by plane an media lens (often lens). F-theta an focused light creates The by space swept adeflector (polygon through a beam, or galvo),and onto a focused 3.9 References tion isanexample. thermal printingapplicationareapplicabletootherendeavors, ofwhichlaserprojec- wholes. Certainly, many ofthedesignconceptsthathave evolved tosupportthelaser classical imaging optics, illumination optics, and Gaussian beam optics into integral media. These systems typically combine the design and analysis techniques from ear arrangement of individually modulated beams and imaged onto a light-sensitive high-throughput printingapplications,wherethelaserlightistransformedintoalin- 3.1 58 In a variety of applications, including longitudinal solid-state laser pumping, laser arrayscanbedesignedinnumerousways, suchaswithphase- mode emitters,uncoupledsingle-modeor effective lightsourceswhencombinedwiththeappropriatebeam that context, avariety of uniquesystems ditional, andtypicallyemploy avariety ofmodernmicro-opticalcomponents. Within are anamorphic inboth physical layoutand beam properties, are themselves nontra- that have been designed to work with these highly nontraditional light sources, which overall device layout,aredependentupontheemitterstructure. The opticalsystems beam profilesandpropagation properties,beamcoherence effects, andthe dramatically. Inherently, many beamproperties,includingtheoutputpower level, the outputpropertiesofbothindividual beamsandtheensembleofvary coupling forfiberlasers,andlineprinters, Although flying spot printers can produce high-resolutionhigh- produce in images can flyingprinters Although spot Traditionally,printer, aflying laser spot in
Opportunities and Conclusions and Opportunities Optics in Effects Thermal 3.8.1 INTRODUCTION
...... Thermal Defocus Thermal ...... 5–12 13–15 laserdiodearrayshave proven tobevery 16 have beendeveloped forhigh-power, the emitted laser light is shaped into into light is shaped laser emitted the a control circuit or indirectly with with or indirectly a control circuit Laser Beam Shaping Applications Shaping Beam Laser multimode emitters, shaping optics. As coupled single- 1–4 fiber 109 110 110 111 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 diode array is used only as acontinuous wave only as is used the with light source array diode (CW)-driven structure. by laser of number channels the a limited to constrained and complicated asubarray, designelements is both optical within the of lasing failure the to printer the desensitizes and crosstalk sensitivitythe thermal to approach reduces this input. While data provide to image the modulated individually Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser printing on insensitive threshold-effect media (0.2–0.5 J/cm on insensitive (0.2–0.5 media threshold-effect printing deliver (15 resolution dpi) throughput high high dots/in; and (2400 proofs/h) while which simultaneously markets, arts have for graphic produced the been printers media. the lengthofdrum,witheachchannelresponsibleforprintingaportion coupled intoanassociatedopticalfiber, withthesefibersarrangedlinearlyacross of ways. For example, the print-head can employ a multitude of laser sources, each directions. scan slow the and fast scan the both to perpendicular zdirection, alongpropagates the light laser The slow moves along the print-head direction. the scan perpendicularly while one providesdirection, in operation media fast scan image-recording the ing carry drum of rotation the printer, drum external an system. in By comparison, the large field optical monocentric rapidlythrough ofa rotating is deflected beam the stationary, while media holds image-recording the printer drum internal The drum. or external drum internal an in may held be media onbed, aflaton. The printed be can media entire the such that over drum swath-like manner arotating complexitythe system. optical of More the typically, is moved aprint-head a in AgX high-quality (silver than halide) which is finer media. photographic dpi, layer. providecoated resolution can image 3000 as media of high as these All a within polymer changing phase and include media polymer cross-linking thermal employed (light)heat are that locally. is applied by exposure laser mechanisms Other works bymedia impression adye when an or ablation sublimation create to process and the beams are directed onto the media. onto the directed are beams the and lasing elements (one subarray), per of agiven beams into is combined beam subarray la thermal andelectricalcrosstalkwithinthediodelaserarray package. results. Furthermore,theseprintersarealsosensitive toimageartifacts caused by susceptible to the failure of even one element in the array, because a pattern error when theindividual laseremittersareimageddirectlyatthe media,theprintersare compared withthesystemsthatcouplenumerouslasersto opticalfibers.However, densities. Suchsystemspossessbothalower unitcostandhigherlightefficiency, as individually addressable to provide the desired modulation to obtain the various pixel imaged directly onto themedia. laser arraycanbeusedasthelightsource,withlineararrangementofemitters creating anarrayofwritingspotswithaseriesfiber-coupled lasers,amonolithic brought togetherintoasmallprint-headtoformlineararrayofsources.Ratherthan titude of laser sources is individually coupled into optical fibers, and the fibers are sing element split into an array of subarray laser sources. Light from each of the of each Light the from sources. laser sing of element subarray array split an into More commonly, systems have or laser alaser wherein designed printing been A multichannelprint-headforaswath-type printercanbeconstructedinavariety because of flyingprinters spot in used rarely Multiple are print-heads channel Alternately, the monolithic diode array source can be constructed with each each with constructed be can source Alternately, array monolithic diode the 17 Alternatively, an integrated print-head can be provided, 6 Inthiscase,each of thelasingelementsmustbe 7 Each of the subarrays is directly and and is directly subarrays of Each the 2 ). Typically, thermal 18 wherein a mul- 59 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 interactions. pipe or as flood illumination. flood or as array, beams light modulator light incident individual either on aspatial as 60 able detail, laser thermaltransferprinting, whichhasbeenpreviously discussedinconsider continuous-tone, referredto ascontone,andhalf-toneprinting.Continuous-tone requirements. For example, laserthermalprintershave beendesignedforboth to thepropertiesof the thermalmediaandprinter, as welltheapplication laser-writtenthe spot. dot and gain properties, plate, ink laser-written on the printing areas unexposed exposed of and the properties surface the but also process thermal laser of the is quality dependent upon not only the quality print suchplates. the cases, In photoresist-coated (3) conventional plates, and laser-written printing printing directly approve to colors, content image and (2) run the press the for films contact exposing (1) are: proof for buyer the Some intermediates of of these thermal laser inks. the multicolor with press by of a high-speed viewed preparation printed the images in production of is the intermediates printing of use thermal laser principal cies. The viewable directly produce to or transparen on paper used images be can printing (3)dye (4) and asupport, from polymer cross-linking, change. thermal phase Laser of ways:variety (1) dye (2) adonor sheet, from or sublimation transfer ablation of a in previously, image noted As an form to amedium with interact can laser the 3.2 uniformizing optics, such as a mirror assembly, optics, such amirror as uniformizing incorporate to necessary tionable become it level Thus, can of artifact. image an objec- in resulting image, usually pixel density fields with printed the on avariable into translate will plane modulator atthe nonuniformity illumination this compensation, or Withoutcorrection nonuniform. significantly be tion can - illumina resulting the micrononuniformities, and have diodes laser macro- both array. However, light emission profilesprovided direction by array the as the modulator of length the entire illuminate to magnification athigh imaged such is systems, In failure. emitter each emitter laser to desensitized array, are fromlight a laser by is flood-illuminated array modulator systems, which the in these addition, power modulation. In atfull withoutit direct operates as simplified is greatly source laser The spots. of printing array an as media the in 2005. in Kodak by Eastman acquired turn was in CREO and Scitex 2000, (Israel) in Graphics Co., &Electronics (China). Ltd Inc. (Burnaby,Machinery BC, CREO CA) acquired Co. (Kyoto, Ltd Manufacturing Screen CRON Hangzhou well JP) and Dainippon as (Belgium), NV Agfa Graphics and NH), (Hudson, as LLC (Rochester, Presstek NY), Company Kodak including ofpresently Eastman offered companies, by avariety properly illuminated. A laserthermal-writtenimagecanbegeneratedinavariety ofways according Computer-to-plate (CTP) laser thermal printers, platesetters, or newsetters, are or newsetters, are platesetters, Computer-to-plate printers, (CTP) thermal laser
21 within the system design, such that the spatial light modulator array is array light modulator system spatial the design, the such that within PRINT-HEAD/MEDIA INTERACTION PRINT-HEAD/MEDIA 22 issummarizedheretoprovide abetterunderstanding ofhead–media 9, 11 , 21 The pixels of the modulator array are imaged onto imaged are pixels array modulator The of the 9 Laser Beam Shaping Applications Shaping Beam Laser afly’s eyeintegrator, of the ink from from ink of the 11 or alight printing printing typical typical 19 , 20 - -
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 tion ofthelight.Heatbuilds upatthedonor’s lower surface inthethirdpanel dye farther along thebeam’s propagation path as aresult of thedye’s attenua- where laser irradiance is greatest. Dye nearest the laser captures more heat than the dyeinsecondpanel,withfastest heatingoccurringatthebeam’s focus, laser isfirstactivated intheleftpanel. Accumulationofthelaser energy heats ning fromlefttoright,atfoursuccessive times. The dyelayeriscoolwhenthe dye layertothereceiver’s surface. The sequenceofpanelsillustratesalaser, scan- donor atafixed gap fromthereceiver andminimizestickingoftheheat-softened coated inabinderonthebottomsurface ofadonorsheet.Mattebeadsholdthe light. room in performed be can handling material all and is needed, processing chemical images.further well-defined produce No donor can the across scanning raster during laser of the volume irradiance small donor. of beam the the Controlling a within rise incident alarge, rapid focused induces the light which temperature then by of dye’s absorption the is initiated process than This temperature. vaporization higher areceiver to when temperatures to adonor is heated transferred donor and low-molecular-weight particular, In dent radiation. laser the from dyes vaporized are of of its visible coating amounts ate dye areceiver to by inci the when stimulated donor for suited intermedi continuous-tone applications is capable of transferring thermal laser The donor media. is the medium of thermal alaser exemplary type One 3.2.1 FIGURE 3.1 FIGURE Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser Figure 3.1depictsavertical sectionofalayerinfrared(IR)andvisibledyes L aser
Schematic representation of laser heating and transfer of absorbent donor. of absorbent transfer and heating of laser representation Schematic T and IRdy Be Receiver herma Vi ad ga support Ke la Donor sible yer La syst y: Lens p se em r e l Cool M edia Wa rm V x Ho tV ap or 61 - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 heat tothesurroundingunexposed donor. laser’s heattrailonthedonor cools backtoambient temperature bydiffusion of some ofitsheattothatsurface, warming partsofthereceiver. Materialinthe the potentialformodulatedimagedensity. Dyecondensingonthereceiver imparts irradiance. Thicker depositsofdyecanthusbeformedonthereceiver, providing are removed, greaterdepthsofthedyelayer are uncovered withcontinuedlaser donor. The fourthpanelshows thatasdyemoleculestransferredfromthesurface sol, whichcancondenseontothecoolersurfaces ofthereceiver andsurrounding transforms thehotmoltendyeintofreegas molecules, orpossiblyintoanaero- ization temperatureacquiresitsheatofvaporization, thenthisadditionalenergy causes thedonor’s lower surface toactasathermalinsulator. Ifdyeatitsvapor because insignificantthermalconductivity orconvection atthedonor–receiver gap 62 tion to the amountandheatcapacityperunitvolumetion to the {ρ vates thetemperatureofdonormaterialabove theambienttemperatureinpropor inthepresenceofthermaldiffusion. The absorbedlightenergythe temperature ele- the fractionofheatescapingbythermaldiffusion provides anapproximationfor Multiplying theresultingstatictemperaturebyaproportionalityfactor representing out the dye layer, which can be calculated by simply accounting for energy deposition. thermal diffusion, ascanningsourcegeneratesuniformtemperatureprofilethrough- approximation and,morecompletely, asadynamicphenomenon.Intheabsenceof laser lighttoconvert thevisibledyetoitsvapor phase. the dyeistransferredonlyfromregions thatretainenoughenergy fromtheabsorbed profile acrossthethicknessofheateddyelayer. intense depositionatitsentranceintothedyelayer, furtherleveling thetemperature thin. Heat diffuses into the cooler plastic support and away from its location of most fuse through the thickness of the dye layer. By implication, the dye layer is width athalfmaximum(FWHM)islongerthanthecharacteristic timeforheattodif- scans slowly enoughsothatthetimeforbeam’s centertotraverse thebeam’s full in the nearby material. This buildup of heat at the outer surface occurs when the beam donor materials. This outersurface actsasathermalinsulator, causingheattobuild up is provided, whichhas an extremely smallthermalconductivity comparedwiththe through thesupportbecause,atoutersurface ofthedyelayer, amildvacuum the lightdeparts. The uniformtemperatureapproximationisrelevant forlightincident deposited onthe side through which the light enters than on the side through which mation canbemade,even thoughtheBeer–Lambertlaw indicatesthatmoreheatis exposure. As partofthestatictemperatureanalysis,auniformapproxi- decomposes some constituents,andmechanically deformsthedonor. of thatenergy presumablyvaporizes volatile molecules,furtherheats nonvolatiles, to bedevoted totransferringthevisibledye fromthedonortoreceiver. The rest the energy beyond that neededtoheatthevisibledyeitsvaporization pointseems contains lessmaterialtobeheated initsdyelayer. Onlyasmallfraction(~ 3%) of than byathicker dyelayertoattainthesameimagedensity, becausethethindonor the surface ofthedonor. Ingeneral,lessexposure isrequiredbyathinnerdyelayer constitutestheenergyof threshold available fortransferring thedyemoleculesfrom The thermalprofilewithinthedyelayercanbeanalyticallymodeled The typicallaserthermaldyetransfermediumisathreshold medium,meaningthat Laser Beam Shaping Applications Shaping Beam Laser c ρ } of material capturing that } ofmaterialcapturingthat 23 The exposure inexcess 22 as a static asastatic thermally thermally - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 by writingadjacent channels,occurwhenthe opticalwritingspotislarger than the neighbor spots. Nearest-neighbor interactions, which increase the output density provided are extended acrossseveral neighboringwritingspotsinsteadofonlytothe nearest- the swath responsetohidetheintensityandplacementerrors, because interactions modulation transferfunction (MTF) andmakes itmoredifficult tobalanceoradjust put inthermalmedia.However, theuseoflarger printingspotsalsolowers thesystem density. transferred tinuously adjustable thermal laser con with images producing printers, thermal laser donors in of consistent thickness translating for apparatus precise the use justifiesof amechanically demand This a50 µ within maintained dye receiver 0.1 on the the less to layervariation than Drequires donor of be to the focus best to hold from 3.2, is shownthat adensity Figure which indicates in distance basis. over-layers laser-heated the layer through internal expands abruptly on alocalized eruptive by an operate also can media layers. thermal Laser using pigment fabricated are media thermal laser many particular, In media. transfer layer cooler where support. it the contacts dye of the interface deposition internal spite of atthe in more initial heat ofand the dye interface, of of the that outer layer interface character aresult insulating of as the exposed atthe occurs temperature hottest the speeds, At slow-to-moderate scanning attained. away, temperature diffused has maximum beam the of reducing the half hot. However, as location twice that make some deposited by leading heat of the the subsequentlyto attempts beam of the half trailing The beam. of the half leading the only received has center lightfrom beam donor atthe the location in the because forsequence exposure onto depositing photosensitive that materials. density, image the time of exposure regardless which uniquely the in the determines fastbetween scans. ambient to temperature cool to substantially donor is permitted the if add lines scan by successivetransferred density profiles the so that slow the sity in direction scan a specific amount, a specific density image drop to focus the best causes from that of distance focus the becomes depth effect, the waist. narrowest In exhibits the that plane the not necessarily and density, uniform highest produces of plane location focus best that the the as that by recognizing density. image ferred determined be of can A focusdepth criterion by movement dye of the layer- away of plane trans focus, best the the from reduces caused beam, tightlyof focused. be Broadening the beam laser the that fer requires - trans induce to order visible in the of necessity heating dyeThe temperature high to 3.2.2 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser cant departure from the additive exposure the from departure cant ance distribution ance The useoflarger printingspotshidesspotplacementerrorsandincreasesthrough- It should be noted that there are types of laser thermal media other than dye than other media of thermal laser types are there It that should noted be center beam instantaneous the donor inevitably the location hottest in trails The considered to obey be additive dye can process den- transfer thermal laser The L aser / M 28 edia 27 (e.g., Rayleigh the range). Arepresentative of curve density versus 23 instead of irradi more conventional using the instead aerial of size the , 24 I This basic property of the laser thermal imaging is a signifi imaging thermal laser of the basic property This n m range about the plane of best focus throughout the image. of plane the focus aboutbest m range the throughout t erac t ion — D ep mechanism of silver imaging, mechanism halide t h
of F ocus process, in which an which an in process, 25 63 , 26 - - -
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 by writingwith asinglespot.Inparticular, writingwith multipleadjacentspots combine inafavorable way, effectively usingenergy thatwould besquandered printing, the thermal interactions of adjacent writing spots on the donor typically sources aremounteduponthe samesubstrateorheatexchanger. Inlaserthermal ence ofonesourceuponanother source’s emission,whichmightoccurifmultiple with multiplesources. These interactionsareseparate from thermallymediated influ- between thetemperatureprofilesproducedindonor by simultaneous exposure media crosstalk(thenearest-neighboreffect) orboth. Thermal interactions can occur 64 sources areinsufficientproximitytoincurlasersource crosstalk orlaser work inparallelbut inisolation,therearealsomany systemswherethemultiplelaser While thereareviablelaserthermalprintingsystemsinwhich multiplelasersources 3.2.3 the useofchannelcompensationandcalibrationmethods half-tone dotonaprint.Furthermore,useofthenearest-neighboreffect alsorequires tion amongthechannelsandadecreaseincontrastmodulationaroundrimof system. The price for this efficiency is the increase in the The increaseinefficiency issignificantindeterminingthe overall throughputofthe in bothspaceandtimewhentheopticalwritingspotismorethanonerasterlinewide. less efficientlythantheenergy fromtwo ormorelaserspotsthatoperateinproximity used is scan line spacing. laser Alternatively, single it can bestatedthat the energy froma donor. thin 3.2 FIGURE depth offocus. and makes nearest-neighboreffects morecontrollablebut alsoreducestheeffective the printing spot size is problematic, as the use of small writing spots increases MTF by multispot print-head in order to strike a compromise among the densities exhibited single, L aser pair, andtriplelinepatternsanentireswath. Thus, thedefinitionof DR, Cyan reflective density of Experimental and measured depth of focus for a “singles” writing spot ona spot of focus for depth a“singles” writing measured and Experimental
/ intermediate laminated to paper M 0.0 Dr 0.1 Dr 0.2 Dr 0.3 Dr 0.4 Dr 0.5 Dr edia −60 μm I n t erac −40 μm t z, Distancefromnominal ion −20 μm0 — M u 0.135 J/cm Mo lt isource deled densityfor0.129J/cm deled μm2 Laser Beam Shaping Applications Shaping Beam Laser 2 =
Print-head tilted to reduce spot pitch (Y), while maintaining a constant aconstant maintaining while pitch (Y), spot reduce to tilted Print-head 1 Y 2 Prin 3 t- head tilt 4 d % or less), have that adja those as the - and 5 σ V y x 6 7 n 31 – 35 The tilting of tilting The 60 % 13 , –80 14 These These of % of 65 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 beam does from its first-leading neighbor. from does beam dummy preceding by advantage of this same preheating enjoys print-head dye the in on laser its second own.for the nearly The transferring of nearestneighbors ing whileavoiding theneed totilttheprint-head.Interleaving canreduceinteractions print-head withitswritingspotsspacedfarther apartthanthedesiredscanlinespac- operating this leading laser as a as laser leading this operating avoided be can by swath edge artifact image. This the in of alight line artifact the causing print-head, the in power lasers other same the atthe less as dye operated if transfers laser leading the beam, any other from tail advantage ofthe a thermal 3.3 of Figure print-head not does have swath tilted of the the in laser leading the Because beams. by trailing unchanged activating or the deactivating spot are leading conditions present for a thermal the because diffusion, thermal size, spacing, and conditions of relative spots, beam by leading experimental the the to transferred dye to not to contribute assumed are spots lagging the particular, In beams. leading away. lines another, spot to twolaser raster from one little energy extends as very insignificant, be to is predicted interaction Conversely, arrives. adjacent of beam the lagging part second-neighborhottest the when the available medium the spot’s in ing remains its exposure skirt from heat neighbor preceding of a portion where asignificant dissipation occur conditions can time Thermal distributions. thermal lagging and leading between for difference the provide considerable lowstill benefit can print-head factor fill evenaccounting when successivethe adjacent exposes an location. spot source lagging Nonetheless, atilted 66 the array direction, the first-order writing spot size can be derived from the systemfrom derivedbe can spot size writing first-order the direction, array the applications less have resolution other size, although (25–50 required spot (or writing 2.5–10 dpi as range, the pixel) µ small as 3000 be to may need 2400– the in high-resolution printing applications require graphics of many As the 3.2.4 ficed as dummy lasers. as dummy ficed However, sacri are nearest-neighbor no interleaving lasers as the lacks interaction, spacing. line scan by varying profile shifts of temperature or accentuation a print-head avoided, be can nearest-neighbor artifacts because ing advantagean interleavbe for nearest-neighbor can interaction ofpoint insignificant last a single swath. exposedThis during lines of spacing scan result greater of the as a nearest-neighbor is insignificant the interaction because printing single-source much as (3) area-averaged exposure as densityproduction requires of and adesired image,completeto an scans extra requiring never in, are filled area the scanned edge of trailing edge sequence, (2) and leading of the ordinal part their in written gaps betweenscanlinesfromprevious swaths. size intheslow scandirection.Onsubsequentpasses,linesarewritteninthe Alternately, interleaving orinterlacing In the case of the tilted print-head, lagging beams providethe benefitto little beams lagging print-head, tilted of case the the In The principal disadvantages of interleaving are as follows: ofas disadvantages interleaving are principal The (1) not are lines scan L aser / M edia 25 whilemaintainingconstantprint-headscanningspeedorstep I n t erac t dummy ion — S
laser po 32,36–38 t S 33 ize , 35 enablestheuseofalow fill factor at a power just below threshold the , S Laser Beam Shaping Applications Shaping Beam Laser hape 39 such as difficulty balancing balancing such difficulty as , beam as each subsequent each as beam and P rofi l e µ m spots). In m in m in - - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser propagating from left to right through a material with higher refractive higher index with n a material through left right to from propagating continuous thick, curves the represented by is waist beam actual profilethe the of diffuse the mode structure. mode the diffuse by the removal of higher order time variant modes by removal variant the time of order higher way. arandom means, in by optical nonuniform mitigated various be effect can This pixel be can printed of donor. the densities area image a larger within the aresult, As amount powerof dyeovertransfer uniformly that same more efficiently spread than thermally will beam writing the regions within high-irradiance especially these then profile, temperature local the enough large persist modify to long are enough and focus best different hot with positions hot spots spots producing extents. these and If beam, main focus light to the from that causes differently that coherence spatial converging have the multiple the light beam within a localized modes particular, In pixels. printed of the quality image the in degradation in resulting focused beam, the from profile of energy focus depth the the and both affect also can printing thermal spots. writing Gaussian nominally the with compared as nearest-neighborinteractions reduced to be experience expected spot profilesing can per-pixeltendconverge.to writ will profiles energy uniform Systemswith nominally fast the net effect that the and with slow aberrations, and scan by diffraction rounded be at somewhat least per-pixelwill ofarray auniform light profile ata modulator image The profile. heat) and (light energy a more fastuniform into scan the smears pixel the writing during media the across motion beam Gaussian of the the direction, slow the in scan uniform and direction fast scan the in spot is Gaussian writing the light profile,that per-pixel at on a least uniform instance the In exemplary basis. array, of a modulator length the entire present which a nominally flood-illuminate However, Gaussian. nominally be also several systems, are that such those there as may (slow the media orthogonal to the light profilepresented the or array) axis, scan In profile Gaussian the media. ontospot focused anominally presents cross-emitter) or cross-array to which (typically fast corresponds which scan, the at least one axis systems havein printing configurations thermal Many spots. laser writing the within section. cross in or square round often are media of light incident laser the to spots writing the practice, In spot specification. direction (narrower) array the than the media may motivate a cross-array printing spot specification that is different (convolution) smear resulting the spot and writing the to across heat light and of the relative media and (fast motion drum of the cross-array the scan) the In direction, effects (e.g., media effects, and specification. optical inks) with may the alter dot gain lightincludingprofile,the nearest-neighboralthough factors, other dpi specification, radius at its narrowest waist as it does in the absence of that slab. of absence that atits the it waist narrowest radius as in does Conveniently, slab, incident same on a dielectric the has normally beam, a Gaussian media. the within focus best waist position nominal is shifted the such that media the with interact will beam afocused notable laser Gaussian One subtlety is that criteria. imagedensity of focus adepth uniform defined by within media coincide the with n 1 of the surrounding air. The solid arcs are segments of the actual phase fronts for fronts phase actual segments of the are solid arcs The air. surrounding of the The multimode lasing behavior intrinsic to many diode laser sources used in laser laser in used sources laser diode many to lasing behavior multimode intrinsic The light profile dependent upon the be pixels also can printed of the quality image The In Section 3.2.2, the point was made that the tightly focused laser beams should tightly focused beams laser the that was point Section 3.2.2, made the In 41 40 or by homogenize or optics that 42 In Figure 3.4, Figure In 2 than than 67 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 side of the medium with the index n the with side medium of the conservation of the beam’s ofconservation the energy, ω then
propagation direction propagation waist beam’s narrowest along the that zfrom atany single distance determined all wavelength the and λ front, phase Rof beam the of the of radius curvature local the 68 at the media interface on the air side, and a resultant radius R radius side, aresultant and air on the interface media at the were higher-index removed. the if materials waist beam wouldthe that follow profile the are curves dashed The beam. laser that 3.4 FIGURE (
dependent parameters. The incident beam has an initial radius R radius initial an has incident beam The dependent parameters. in which the radius of curvature and wavelength and only refractive the index- of radius are curvature which the in Thus, medium. that upon entering outside the medium ω outside medium the waist just local the Likewise, because axis. optical the with law angles relates their considered rays therefore,be can and, fronts phase the to lar similar equation similar propagation obeys zof beam a direction location along waist of the radius The the ω 02 The narrowest waist radius ω waist narrowest radius The Therefore, the radius of curvature must enlarge by medium’s must the enlarge of radius Therefore, curvature the refractive index ) as in air for normal incidence ( incidence for normal air in ) as
A Gaussian beam’s waist has the same minimum radius ω radius minimum beam’s same A Gaussian the has waist 43 , 44
43 1 , is identical to the local waist just inside the medium ω waist just local medium inside is identicalthe to the 44 in a material of asingle refractive index: amaterial in n 1 n 2 ω 0 ω is uniquely determined by the local waist radius ω waist radius by local the is uniquely determined z 0 2 ω 01 = = 2 ). 01 - perpendicu are of curvature radii the . Because 1 n R 1 1 1 + + ω = 1 02 =ω πω R ω λ n R πω λ 2 R 2 2 R 2
2 2 . 2 2 Laser Beam Shaping Applications Shaping Beam Laser
2 of the beam, Snell’s beam, of the and waist ω and 1 , a beam waist ω , abeam 0 inside a medium amedium inside 2 on the on the (3.2) (3.3) (3.1) 2 by by 1 , ,
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 resulting print density. print resulting the and of is transferred donor quantity of that the quality, terms in print thermal waist. However,focusing beam lens the to laser the affect offset can ultimately the the from distance the than thinner are much order that first to for neglected donors be can media thermal laser the waist in position offset the beam of in the This consisting of a series of small, distinct light emitters. For state-of-the-art high-power For state-of-the-art light emitters. distinct ofconsisting of small, aseries 3.5, Figure in source, is asegmented discern to small too itself, are whose features air- or water-cooled packages, well array a2D form array. to as laser stacked as The in configured be can arrays laser These contact. mechanical thermal and electrical well as quality as radiation, emitted which provides the to access working structure, 10,000 h beingreported. laser diodearrayshave proven tobegenerallyrobust, withlifetimesinexcess of laser diodearraysspanninganarrower range(~ a narrower wavelength range,from~ from thevisibletonearIR.Laserthermalprintershave beenundertaken over cavity (VCSEL) structures, while the lasers span an emissionwavelength range been used,includinggain-guided structures,index-guided structures,andvertical multimode sources,andsources. Various gain structureshave also comprising various modestructures,includingsingle-mode sources,single-by- Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser refractive of by ratio indices. air, the the in than laser arrays from theefforts tocontrolthebeamemittedfromlaser diodearrays.Diode majority ofthenew solutionsinlaserbeamshapingforprintinghave emerged radius radius narrowest aconstant waist maintains beam the aresult, As of radius curvature. the reduction of wavelengthThe of ahigher-index enlargement in the cancels medium is relationship two wavelengths media between different in The beam same of the or arrangedintoamultibeamprint-headwithsecondary arrays, althoughafew have employed discretelaserdiodes,either Most ofthelaserthermalprinterdesignarchitectureshave employed laserdiode 3.3 The typical high-power laser diode array package (see high-power 3.5) array acompact diode Figure typical laser has The
LASER SOURCE CHARACTERISTICS SOURCE LASER ω 0 , but the refracted beam waist higher-index plunges the into beam deeper medium refracted , but the 47 have beendesignedandfabricated ingreatvariety, witharrays z 2 = 1 + λ R πω 22 2 R 2 2 2 = nn 11 1 λλ + 800 to1016nm,withthehigh-power IR = 22 n n 1 2 λ n n
1 1 2 πω R 800–980 nm). These high-power 1 2 2 n n 2 2 R 11 combining optics. 2 = fiber-coupled n n 1 2 z 1
46 17, The (3.5) (3.4) 18, 69 45
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 70 emitters, each 150 each µ emitters, Power example, Opto an As an 19 laser comprises OPC-A020 multimode array 3.3.1 (definedin Lagrange Section 3.3.2). and (NA),coherence, profile,beam relative beam aperture different, numerical to considerably cross-array) (array are and two directions the light in emitted of the DE), (Jena, Jenoptik properties and DE). beam GmbH (Mainz, The Diodenlaser CA), CH), Coherent Inc. (Santa GmbH (Zurich, Clara, DILAS Enterprise Laser availableincluding II-VI companies, numerous are from power arrays diode laser IR (San Labs (Tucson, Jose, Spectra-Diode Corporation and CA). AZ) Presently, high- Historically, devices were these Power such available Opto as companies from els, including 10, nm). W, 80 (790–980 and 40, IR near light emission the with in modulation. laser asystem direct with than more complicated is system inherently employsoptical source laser that the to external amodulator provide to (or ofand number alarge modulation channels pixels). Admittedly, an modulation performance the optimize to advantages, opportunity includingcant the several has signifi array or modulator modulator external of use an modulation. The of the quality the degrade can emitters the between crosstalk thermal locking) and (phase crosstalk optical because but also pathways electrical is required, the that in separation of not the only because is not trivial, array diode a laser within ters or emit- channels addressable basis. on aper-channel individually signals Providing provide to drive thereof, must addressed or groups be emitters, laser individual the Otherwise, advantage for arrays. diode laser is a particular This light. emitted the modulate directly to they the lack ability because significantly simplified thus are themselves light modulation device. lasers The aseparate illuminate that sources device. the across over distance asubstantial apart spaced periodically which are sources, multimode are emitters these arrays, Switzerland.)II-VI Zurich, Enterprise, Laser 3.5 FIGURE enables these lasers to provide to outputenables power lasers high very these levels area, small avery from of length 11.85 pitch direction overall emitter-to-emitter large array an The mm. High-power diode laser arrays are available at various rated output available power rated are High-power at various lev arrays laser diode CW, in operated light as are arrays laser and lasers designs, of many the the In L aser
An exemplary laser diode array package, the BPC808-40C-622. (Courtesy of (Courtesy BPC808-40C-622. the package, array diode laser exemplary An C oherence m wide (w), on a650 µ apart spaced which are
and B eam S hape I ssues Laser Beam Shaping Applications Shaping Beam Laser m pitch (p), for - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser the irradiance profile. irradiance the in rippling resulting the and without modulator interference atthe superimposed be can emitters various the light from one with another, the not phase-coupled are ters emit the as Furthermore, approximate. most lasers that light sources point the than rather coherent extended sources, or partially incoherent miniature approximate ters ter width: ter
incoherent temporally, with a short coherence length C temporally,incoherent length coherence ashort with emissionfairly large ( bandwidth have these lasers profile.As a beam laser), angular but non-Gaussian a very with array direction, the light is emitted into arelatively into light is emitted NA the ( small direction, array Typically, emitters. effects between crosstalk the in thermal minimizing while still FIGURE 3.6 FIGURE
timode emission havetimode reported. been - mul uniform agenerally with emitters laser although nonuniformities, microspatial and macro- both has beam array the tionthat light emissionresultthe profile,with - direc array the to roll-off is ageneral there lasers, many In interference. intraemitter from rippling 3.6, shown as Figure in is relativelyemitters, minimal with flattopped fieldlighteach near the profile,across of direction, overall array the aresult, As emitter. each across incoherent is spatially direction array the in light emitted the ofeffects, largely filamentation free are lasers the that assumption Given further the length oflength ~ acoherence and bandwidth nm a40 with emitter LED an with compared course, Of interval) interval) (or coherence width coherence the source, uniform incoherent an as beam direction C 49 I 15 15
of these lasers is small compared with the 150 the with µ compared is small lasers of these
A measured near-field beam profile for a multimode emitter. multimode profile for a near-fieldbeam A measured µ m, these lasers are still relatively coherent. Approximating the array relatively still array the are lasers coherent. Approximating these m,
Irradiance 0.0 0.2 0.4 0.6 0.8 1.0 C I C Δ = L λ 20 ) of ~ == ×× ∆ 50 λ NA . λ 2 In effect, in the array direction, the emit the direction, array the effect, in In 16 3–4 nm for nm a laser, output light is nearly the 3–4 Distance 0.2 mm λ ≅ 2 µ
m
L : 48
m array direction emit direction m array ~ 0.13 for A020 the (3.6) (3.7) 71 - - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 72 must be well understood in order to design a laser thermal printer. In particular, particular, In printer. design to order thermal alaser must in well be understood coherence, that array, than diode laser of other the properties numerous are There 3.3.2 (TE single-mode transforms Fourier frequency spatial dominant index), The width. stripe the and nonlinear and factor enhancement (linewidth device parameters material microscopic is pumped, the upon howdepends that frequency hard spatial a dominant has filamentation The is evidencelaser. of the doubled-lobed some near-field structure within filamentation center. the in dip The pronounced with bimodal is often and peaks sharp has rather (NA ~0.07–0.14)is narrow but profileuniform is not the cutoff is sharp, the and extent angular the While direction. multimode the in light output emitter by an 3.7 FIGURE ( is output over direction amuch NA larger cross-array the in light emitted The light. the seen distributions multimode for and bimodal uniform the than rather profiles, field andfield near far profiles light the beam propagation. both Thus, Gaussian have the beam width (typically approximated by 1/e (typically width the approximated beam the direction) of any given fast is coherent axis over (laser emitter direction cross-array the in light output. Bythe effectivelyemitted definition, forcing diffraction-limited only mode, one laser supports that wave formed structure epitaxially guiding an of of array smile array cross- the by modified over array, further as entire light is integrated the cross-array of coherence the spatial The interference. and phase-coupling without cross-array combined be can beams the thus, and, emitter to relationship emitter phase from is no common there beam, direction acoherent outputs cross-array emitter laser ~ 0.63), corresponding to a cross-array direction Gaussian beam 1/e beam Gaussian 0.63), direction across-array to corresponding H By comparison, the light emitted in the cross-emitter direction is a nominally is a nominally direction cross-emitter the in light emitted the By comparison, 3.7Likewise, Figure shows arepresentative of far-fieldlight distribution the for = 2× L aser into two lobes in the far field. far two into the lobes in λ and limitations from the optics. the from limitations and
/( A measured far-field energy distribution of a multimode emitter. of a multimode far-fielddistribution energy A measured π A 0.85 µ =0.85 × NA) 00 rrays ) beam that behaves according to the principles of Gaussian beam of principles beam Gaussian behaves the to that according ) beam
as L igh FW m. In the cross-array axis, the emitters typically have typically emitters the axis, cross-array the In m. t = 12° S 10 HM ources θ 51 II (d 51 0 eg re 5 e) 0 Laser Beam Shaping Applications Shaping Beam Laser 2 emitting width). emitting each Although 2 emitting width width emitting Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 beam ( beam junction direction the to corresponds Relative direction asingle array to emitter, the 3.8. Figure in is depicted direction, cross-array the single in mode and direction of thespatialandangularemittingwidths). tial andangularemittingareas),orone-dimensionally, astheLagrange(product optical extent canbecalculatedtwo-dimensionally, astheetendué(productofspa- An opticalsourceischaracterizedbybothitsphysical andangular extents. The array also corresponds to the cross-junction direction of the laser diode structure. structure. diode laser of the cross-junction the to direction corresponds also array laser of the direction cross-array The modest divergenceemitter, only the is retained. amodest divergence. with Gaussian However, multimode of present case the the in Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser invariance ofthepropagation oflightandtheconservation ofradiance must laser of correlate. the emission characteristic the and media the at spot the systemoptical the case, light efficiency suffer.this tion; otherwise, In will applica - well the to be matched light source the that importance paramount it is of direction, each emitter is nominally a coherent single-mode (TE is nominally emitter each direction, L as estimated be can Lagrange emitter the and coherent source, or partially incoherent is an emitter array laser typical the direction, above, discussed array by-multimode As the in emitters. laser atleast one row comprises of single-mode- array laser when the array), particularly (arraycross- and two values meridians the in Lagrange different have dramatically they because light sources atypical are arrays diode Laser used. is more commonly system, nonorthogonal Lagrange rare the only in tracked be to etenduéBecause needs design phase. the during Lagrange etendué or the the tracking to simplify otherwise sity (irradiance vignetting are ignored. and system, optical scattering, given an light absorption, that throughout constant or is conserved Accordingly, radiance law the of conservation of per radiance, the at the half maximum or ~ maximum half at the widths these estimate to profile, practice it common is some to gradual off according extents, butfall rather angular or do notthe havespatial sources edges define to hard absolute, notlight values be As most need lated be useful. to but sufficientlyaccurate light convergence and calcu spot size plane. The desired target the atthe in resulting system, the through tracked then are and light source atthe calculated values are the product of the emitting spatial area and the emitting angular area (in steradians). area angular emitting the and area spatial emitting ofproduct the the powerpower optical the by as divided density atagiven which is estimated surface, the optical quantifies that term is aradiometric Radiance ofconservation radiance. calculated fortheoriginalsource. be conserved atany andevery opticalsurface withinthesystemtomatchvalue etendué orLagrange(theproductofthephysical andangularwidthsofthelight) integrated over theentiresource.Inmostopticalsystems,itisdesirable thatthe for asourceaswhole,orincrementallyany portionofthesource,andthen light source, and the Lagrange can be estimated as L as estimated be can Lagrange the and light source, A typical laser diode array, comprising emitters that are multimode in the array array the in multimode are that array, diode emitters laser comprising A typical In classicalopticalterms,therearetwo conceptsregarding theconstancy or In most cases, it is sufficient to estimate the optical power power the optical and mostoptical it cases, In isden sufficient estimate to The conservation of conservation etendué (orThe Lagrange) is closely law the to related of the θ ║ ). In a single-mode laser, the emitted light in the junction direction is highly is highly junction direction the light in ). a single-mode laser, emitted In the optical power a system, = optical and throughout area) at key per surfaces 10 intensity levels. % intensity NA × = NA w half width). cross-scan (NA ×half /2 the In 53 These quantitiescanbecalculated
=
ω
× NA = NA λ 00 /π. ) Gaussian) beam 54 In use, these use, these In 52 thatapply. 73 52 - -
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 might be expected, optical systems with these laser diode arrays typically employ typically arrays diode laser systems these optical with expected, be might As appropriate. optics design are principles illumination optics and classical imaging incoherent, generally and light is multimode direction array where the cases many propagation for must followed. be beam practices Gaussian accuracy, In standard the optics with cross-array design to systems. general, the In printing thermal laser the of of many directions cross-array and employed are designs array that optical the in or Lagrange) shaping brightness NA, help and beam laser motivate different very the relative (mode coherence, output emission structure, properties ferences beam in ensemble entire of is, dif nonetheless, The them between substantial. difference the emitting width ( width emitting optics are designed to not see the nonemitting spaces ( spaces nonemitting the not to designed see optics are 74 tively poor beam quality, and is emitted within a large angular divergence ( angular alarge within tively quality, is emitted and beam poor arela with Gaussian, - is generally beam emitted the cross-junction direction, In the 3.8 FIGURE Lagrange of a modern LED emitter ( emitter LED of a modern Lagrange the than much smaller are Lagranges cross-array and array the both Although by approximately differ values times. 700 that Lagrange cross-array and array has (NA ~0.1). low beam the to contrast divergence in direction 0.5–0.6), array divergent ahighly into (NA ~ emitted beam typically light is also laser cross-array of ~ have Lagrange a cross-array is estimated as L as is estimated Lagrange of L Lagrange laser array (19 array laser emitters) is, therefore, ~ single TE single output nominally of emitters laser asingle emitter. the Lagrange laser As alent the to plane. or target media printing the devices and modulating the both encounters (NA) width light efficiency relativethe or optical as angular the to importance bear ( large would Lagrange be fairly laser direction lenslet the with array, array the than rather array. Conversely, asingle with lens, is collected array laser the light from the if lenslet direction-oriented array of use an the achieved be through can emitters, the between spaces without the seeing array laser the light from goal, of collecting latter As arepresentative(theAs example, OPC-A020) array alaser direction array has Thus, it can be seen that the typical single-mode-by-multimode laser diode array single-mode-by-multimode array diode typical laser the that seen be itThus, can In principle, the Lagrange for the laser array in the cross-array direction is equiv direction cross-array the in for array laser the Lagrange principle, the In L
= 00 0.13 ×11.85/2 = mode light as a classical Gaussian laser beam, the cross-array Lagrange Lagrange cross-array the aclassical beam, light as laser mode Gaussian
Emitting geometry of a linear laser diode array. diode laser of alinear geometry Emitting
= w NA ×w ) of 150 µ = λ /π. Thus, an exemplary laser source emitting 830 nm light will light will 830 nm emitting exemplary source laser /π. an Thus, /2 /2 m, and an array direction NA of ~ direction array an and m, 0.77 mm). This difference in the collected Lagrange can can 0.77 Lagrange collected the in difference mm). This ~ 9.75 µ 9.75 0.26 0.26 p m. The array direction Lagrange for the entire for entire the Lagrange direction array The m. L ~ 0.5 mm) ( or a xenon lamp arc µ 187 187 w m. It should also be emphasized that the the that It m. emphasized be should also µ m, assuming that the array direction direction array the that assuming m, ap numer cross-arra Array and Laser Beam Shaping Applications Shaping Beam Laser er La ture p − ser emit ical w s (NA) ) between the emitters. The The emitters. the ) between y 0.13, emitter an has and ters L ~ 3 mm), θ ┴ ). - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 system configurations have systemdeveloped configurations been such alternative as asystem of emitters, one is susceptible or more laser failure the to o 3.3.3 array laser the fiber independently. directed However, and shaped be optics, including specialty other can light beams cross-array and lens array elements the so that cylindrical numerous diode lasers spaced apart on a50 µ apart spaced lasers diode µ by a250 10 into separated gathered or channels, groups which are lasers, diode mode magnification. appropriate atan plane media the to array laser the image to manner, in a straightforward modulator, suchexternal configured be systems can an directly. media Lacking on the systems write to printer thermal laser in used been mirror array, orthelike, isemployed toremove thespacesbetweenarrays. nificantly increasedunlesscross-arraymicro-optics,suchasalensletarray, reflective relatively large (e.g.,~1.8mm),whichmeansthatthecross-arrayLagrangeissig- source forhighbrightnessIRlaserlight. The laserarraytospacingis are used in laser pumping applications, where the ensemble device is an effective multimode laseremittersarestacked inthecross-arraydirection.Stacked laserarrays diode arraysarealsoavailable, inwhichamultitudeofrows ofsingle-mode-by- systems. printing available thermal have laser are in and used sources laser been other Certainly, emitters. a single comprising row array) (a of array diode single-mode-by-multimode linear laser is alaser source laser the that discussion, assumed it been generally has preceding the In Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser wherein the laser emitters were arranged in addressable subarrays. addressable in were arranged emitters laser the wherein was constructed, emitters direction of single-mode array arrangement alinear ing - compris array diode alaser case, latter array. diode this laser addressable In an with lenslet array) that omits the spaces, rather than optics (such as a single combining lens) lens) combining single a as (such lenslet array)that omitsthespaces,ratherthan optics can again beanticipated thatitmightbeimportanttousearraydirectionoptics(such asa may beonlygain guided andmayemitfromalarger active region atasmallerNA. It may beindex guidedandthusmoretightlyconfined, whereasthearraydirectionlight same preciseemissioncharacteristics (suchasNA). Inparticular, thecross-arraylight removed) of~ as anoverall potential array directionLagrange for the entire 160 emitters(spaces well arraydirection, there is a Lagrange per subarray (16 emitters) of 4.3 µ in the the arrayandcross-arraydirections,atL interference effects. significant system optical withoutthe incurring within combined be can not coherent locked) (phase are beams one another. to The beams emitted the that enough apart far spaced are single-mode emitters laser vidual ensemble an 10of as by driver. the its is indi modulated own channels current The m space between groups. Each channel or subarray is composed of is composed 16 or subarray channel Each groups. between single-modem space One exemplary IR (850 nm) laser diode array of this type consisted of consisted 160 type (850 single- of exemplary IR this One nm) array diode laser below, have further arrays discussed single-mode diode As addressable laser also As asimpleextension to thepresumedlaserdiodearraystructure,stacked laser With thistypeoflaserarray, theLagrangeperemitterisnominallyidenticalin lenses and lenslet arrays, are also frequently used in the immediate vicinity of vicinity immediate the in used frequently also lenslet are lenses and arrays, t her 43.3 55 L and throughout an entire optical system. optical entire an throughout and aser µ m. Inpractice,thearrayandcross-array beamsmaynothave the S ources m pitch so that a subarray spans 750 spans m pitch asubarray µ so that
=
7, λ 57 /π to provide emitter redundancy, provide to even emitter = 0.85µ m/π = 0.27µ 58 m. However, 6 However, However, m. Each Each m. 56 m, as 75 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 Research, which provide further aberration control. aberration which provideResearch, further Blue from microlens Sky cylindrical GmbH, or ahyperbolic LIMO from microlens Inc., aspheric Lenses an Doric from microlens index cylindrical agradient be can (FAC) lenses. For the designed into example,collimator fiber axis lens the or fast corrections by special enhanced minimized, be to aberration allow spherical both ( lengths focal short very with microlenses typically lenses are typically include a typically modulation device. the light to the of optimizing part as and NA size beam cross-array the on imposed system significant constraints further may be is used, there light modulator external where an case system. the In handling by media the of focus by depth beam’s the required determined NA is typically relative spot size the desired the pixels The incident to tion defines ) required. (or dpi plane. Typically, media onto the focus beam effects, and the talk the - cross optics minimal with direction array the through beam the array,laser transmit the light from design the is intent collect to typical the direction, cross-array the In 3.4 ences tothelaserbeamshapingopticsemployed inthetwo directions. beams possess significantly different properties, thus imparting comparable differ that seesthewholelaserarray. As previously, thearrayandcross-arraydirectionlaser 76 U.S. 5,212,707. Patent FIGURE 3.9 been developedbeen enable to array. alaser light collection from overall system. of size the the for Concepts self-registering have microlenses also close array, packed in laser be helping the to also optics reduce to can direction array awkwardly become large. Moreover,before light beams propagating the cross- the quickly controlled be to light beams NA allows lens high cross-array also a rod the divergence laser the reduce alesser to extent collimation). (to Use full of less than to used be can they although light beams, employed cross-array the collimate to The cross-array optics, which are only shown in the most only shown optics, basic the which in are way 3.9, cross-array Figure in The
ARRAY AND CROSS-ARRAY OPTICS
Laser diode array package with integrated cross-array and array optics. (From (From optics. array and cross-array integrated with package array diode Laser Cros fiber lens fiber 55 “Rod ) s- ” lens array and one or more cross-array lenses. The lenses. The one or more cross-array and Lenslet array Laser Beam Shaping Applications Shaping Beam Laser 59 These lenses are typically typically lenses are These Las er array 60 ~ 100–200 printing applica- printing fiber µ m), which m), which or rod or rod - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 inefficiency. In the printing systems where the laser emitters are mapped directly mapped are inefficiency. emitters the systemslaser where printing the In over array its length. the in is alack of straightness plane. Most same simply, the from beams emit substrate smile same on the emitters laser not all is that fabrication error laser diode few net effect of The this microns. a spanning error aslowly with usually ideal, offset the pattern from but are varying arrangement, linear aperfect in not located typically image), are emitters laser the However,arrangement. 3.10 Figure in seen be can as (which field is anear projected characteristics directly affect image quality. systems, image other affect In directly characteristics Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser properties, having a nominal emitter Lagrange of λ Lagrange emitter having a nominal properties, were emissive identical in considered be to emitters laser the arrays, diode laser the of properties discussions prior complication.cross-array of the the added In is an lenses, smile except problem the of of that cylindrical array laser efficiency, andof depth focus. contrast, modulation to regard withsystem light significant still but are quality on image impact direct have can aless characteristics laser cross-array the intermingled, are beams ted Lagrange by 10 times or more from the nominal Gaussian λ Gaussian by nominal 10 the Lagrange or more from times cross-array the increase can array laser the across error ofseveral smile microns significantly. enlarged be In to effect, Lagrange cross-array cause the can error smile the LIMO GmbH FAC-SAC LIMO the modules). collimation available power also (e.g., direction are cross-array integrated with butlight, arrays direction array the only in operates and is anamorphic mostlenslet commonly array S-TIH53 or Ohara silica glass. The lenses, molded fused from of cylindrical array FIGURE 3.10 FIGURE indirectly or plane, media onto the directly imaged are emitters systems, laser the printing two conjugate planes the direct other. each the to In with plane target the to surface emitting the by accomplished imaging be can plane media or the Most array amodulator to simply, array laser the from light transfer 3.4.1 tion of a modulator array, the emitted beams are intermingled, are beams tion of array, emitted amodulator the systems- involving printing of many illumina the in flood By comparison, constant. (writing spots) or pitch emitters between distance is no longer the as is used, head print- when atilted Alternatively, asmile. banding as creates appears error asmile which spots, of sequence writing the in arch an as medium ontois the projected positions light source laser diode of the Most directly, inaccuracy the able artifacts. Certainly, an uncorrected smile error can manifest itself as a printing artifact or artifact aprinting itself as manifest can error smile uncorrected an Certainly, Generally, the cross-array laser beam shaping optics comprise an arrangement arrangement an shaping optics comprise beam laser Generally, cross-array the The array direction lenslet array or slow axis collimator (SAC) or slow lenslet collimator array direction axis is array amonolithic The L aser 9,
11 S , A line of printing spots exhibiting laser smile error. smile laser exhibiting spots of printing A line 21 mi to the media to form printing spots, smile can create directly view directly create can smile spots, printing form to media the to l e E rror / 6 and located in a perfect linear linear a perfect in located π and and thus the cross-array laser laser cross-array the thus and 9, 11 / 9, π , 21 11 . This increase can can increase . This in which the emit which the in as an uncorrected uncorrected an as (see 3.10) Figure 77 - - 6
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 optical systems that image intermingled beams, intermingled image systemsoptical that the for fiber havelens the is necessary developed. ator near been correction Smile mirrors out-of-factory CuW on hard-soldered based technology deliver bar submounts laser can and error, (depth media spotatthe formation of focus, the and spit size). a modulator through efficiency)couplingcontrast, (modulation impact significantly 78 5,854,651. 3.11 FIGURE means that numerous is sufficientlydamaging error smile technology, improvements array system laser of the in impact gradual Despite these 3.4.2 arc. for fiber matching to a lens the by bending follow that errors a simple compensated “s”-be can error or “c”-shaped smile the arc, supply the have that (“s” of arrays laser occur. smile Assuming errors can or “w”) pattern more complicated other although of emitters, pattern arched an as exhibited changes. Most typically, array is the smile across stress mechanical the as process develops reasonably smile available. are fabrication length the array bar in Laser packages. For example, µ values devices of smile with only 0.3–0.4 corrector, array. such the One across smile error array, smile of shape ofan independent the the in smile of the not all, most, if have developed correct been can also correctors that that beam at the pupil is shifted to correct the smile at the medium’s atthe smile the correct to plane. pupil is shifted atthe beam that space. position By plates, of each the properly the of tilting collimated in path optical the laser emitters, either directly emitters, laser the intermingled. been overlapped have offsets no are longer and beams by emitter once the the separable coplanar or common optical planes. These latter methods are limited to the practical practical the to limited are methods latter planes. These optical or common coplanar few displacement over microns length. a10–15 array laser mm or skewpower bent negligiblefiber a rayhas the lens effects are crosstalk because but slight with offsets. Cylindrical axis optical the to travels parallel in beams laser Laser array manufacturers have improved their ability to control or reduce smile have smile control to or reduce ability improved manufacturers their array Laser Other exemplary smile correctors allow individual cross-array lenses cross-array allow individual correctors exemplary smile Other There is greater freedom to develop to for image systems optical that freedom correctors is greater smile There 64 L to be adjusted on a per-emitter basis, adjusting the various beams into into beams basis, various adjusted adjusting on aper-emitter be to the 62 62 aser ) shown in Figure 3.11, shown Figure in the into of plates glass inserted aseries comprises
smile error of 1 error smile S Laser smile correction using an array of tilted plates. (From U.S. (From plates. Patent of tilted array an using correction smile Laser mi l e C orrec t ion µ m or less, and most manufacturers offer low-smilem ormost less, manufacturers and 45 or indirectly, or Ti lt ed gla 9, 59 11 7, , Laser Beam Shaping Applications Shaping Beam Laser 61 57 ss plates , 21 The resulting line of collimated of collimated line resulting The to the media. Exemplary smile smile Exemplary media. the to as the beam deviations incurred deviations incurred beam the as 5, 61‒ 64 for smile correction for correction smile m over a5mm 62 , 63 or or Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 single element to be aligned during the laser bar microlensing process. bar laser the single during element aligned be to 3.12) Figure SAC, the platesinto (see availablephase are integrated providing a arrays that have that subarrays arrays laser work thus and well laser offset with mechanisms, correcting beam ofdimensions the FIGURE 3.12 FIGURE compensator. P-V the asingle assigned and be average then can value. phase smile emitter Each (C, smile of S, the or W) type upon the depending binned and scanned be can Lasers by current. multiples increase anominal to of goingcan threshold 100 from nm, smile and current laser with correlates smile case, latter the In temperature. and ing Notably, conditions, including device upon external depends mount also smile laser o 3.4.3 have used been or induced, Alternatively, pitchlarge either distances. natural aberrations, optical Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser PowerPhotonic Ltd (UK) offers a range of smile correction phase plates phase PowerPhotonic offers correction of arange smile (UK) Ltd wedge For or acontinuously example, surface. varying array either amicroprism formof the in made be plate can phase the (smile)pointing is required, correction plates beforephase wavefront the simplest acaustic. the when forms form, only In error. However, pointing refractive with and compensated be can errors these including wavefront errors wavefront optical introduce distortion, ture curvature, submicron level.- facet curva and smile, bar Taken errors, together, misalignment increased. been has Lagrange cross-array the cost but that atthe system error the ing smile to of 0.5 of expressedP-V error, as smile for error aparabolic-type pointing plates correct phase emitter. of each These lightfrom pointing for postcollimation the correct faces that wedge using continuously sur collimation varying fast in axis forrect imperfections Fast axis collimators, as manufactured, can suffer from imperfections at the atthe imperfections suffer from can manufactured, as collimators, Fast axis ‒ 3.0 mrad, and are available in increments of 0.5 mrad. Also, these correction correction these Also, available of increments 0.5 mrad. are in and 3.0 mrad, pera
Phase plate smile corrector. (Courtesy of PowerPhotonic (Courtesy Fife, Ltd., UK.) corrector. smile plate Phase 5 t to broaden the apparent cross-array emitter size, thereby desensitiz emitter cross-array apparent the broaden to ing D ependence 58
of or large area multimode emitters positioned at emitters multimode area or large L aser S mi l e 65 that cor that 79 - - - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 sensitive to crosstalk of the array beam into the cross-array direction. For example, direction. cross-array the into beam sensitive array of the crosstalk to 80 tion of the printer. It can be understood that these systems these that understood be tion It printer. of can the - direc array the to corresponds array laser of the direction array the such that align, naturally asymmetries The direction. array the to corresponds orientation emitter multimode the while direction, cross-array the to corresponds typically direction elements. optical single-mode Relative of the cylindrical arrays, laser variety the to include a will and anamorphic, be typically shaping optics will beam laser the banding. as known artifact avisual minimize to driven by need tolerances, the swath-to-swath be positioning will acloselyas there of then spots, packed array is integrated print-head the tolerances. If those easing potentially direction, array cross- the spot in blurto tend the will or media motion fast drum of scan the The tolerances. optical similar (fastsee generally will printing scan) directions array (slow printing array the scan) cross- and fabrication and process, array by laser the largely be spot-to-spot largely optics, with pitch determined the media will spherical system upon the down, configuration. depending break can generality This directions. cross-array and array for constituent the optics in the Typically, tolerances systems have alignment different printing rather thermal laser o 3.4.4 will alsoincreasethespotsizeinfast axisdirectionthroughincreasedbarsmile. laser current. Thus, increasingthe laser current will increase the outputpower, but it Figure 3.13,inthecaseofconductively cooledbars,lasersmilecancorrelatewiththe to notethatthesmileoflaserbarhasatemperaturedependence. As shown in rents dependinguponthesensitivity oftheprintingplatethatisimaged.Itimportant Burnaby, BC.) ULC, Canada of Kodak (Courtesy 3.13 FIGURE Should the laser array employ laser emitters that are single by mode multimode, are employ that array Should emitters laser laser the the to imaged directly and addressed is directly array laser where the cases In In addition,inprintingapplications,laserdiodebarsoftenoperateatdifferent cur Microns −2.5 −2.0 −1.5 −1.0 −0.5 1.0 0.0 0.5 012345678 p t
ica Measured fast axis laser smile versus emitter position and laser current. current. laser position and versus emitter smile laser fast axis Measured l A l ignmen t I ssues I =60A;SmileP- I =40A;SmileP- I =20A;SmileP- Emitter # 91 011121314151617181 Laser Beam Shaping Applications Shaping Beam Laser V =2.7μm V =2.05μm V =1.75μm 9, 11 are generally very very generally are 92 0 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 submicron positional tolerancesseeninotherlaserapplications. positional submicron cylinder lens elements canbearelatively relaxed ± unheard of.Bycomparison,thespatialmechanicalalignmenttolerancesfor lens elementscanbeasmuch~10arc/min,tolerancesof±2arc/minarenot tion light propagation. light tion - direc array on the propagation than beam cross-array effect on the more dramatic Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser a slight able laserdiodeemitterstothemediaplane.Inoneexemplary system address of directly array an is image to printer for providing thermal alaser tecture simplest pixels optics, mostimage the obvious and without any intervening archi Aside contact from printing, 3.5.1 sources. diode of laser system have arrays, concepts developedlaser been also 2D arrays with for writing (1D) using one-dimensional systems, primarily printing atlinear sion is targeted discus- this Although field-replace to systemsof the offerlasers. potential the failed some although sources, laser of individual or failure degradation the to is vulnerable system laser multichannel resulting the cases, any of these In media. the to mapped modulation devices before external being individual with equipped be also can sources The laser indirectly, fibers. of by optical media means the to routed be can Alternatively, media. the to beams laser mapped the are emitters laser the and data, image with addressable directly are emitters laser the cases, many In cost structures. most lowest compact designs the provide the with spots potentially of printing laser series to a directly correspond sources laser discrete in of series a which figurations system the printer, con- for thermal laser a multichannel a designAs architecture 3.5 would provide likely uncorrectable line artifacts. would line provide likely uncorrectable for via corrected potentially be array. laser the However, across emitter can laser to emitter variability emitter while laser susceptible from systems of response Both a variable to are these media. the ontofashion magnified in is imaged lasers emitting of surface array which an in Likewise, aslight θ propagation (spot planes), beam the critical in in size well effect. as a rotation as changes which could cause dramatic direction, poweroptical cross-array the into receiver. system Asimilar on aper-pixel dye donor in basis, the to the resulting evaporation from transfer and Heat is generated print. on the apixel to aline in corresponds diode laser each that such media, onto the directly array laser the opticssystem image to spherical uses optical other. independently controllable simplified each and from addressable The on a single semiconductor but substrate, is individually integrated is monolithically Company (shown Kodak 3.14),by Figure Eastman in of diodes laser array alinear Not surprisingly, although therotational alignment tolerances for the
DIRECT LASER TODIRECT LASER MEDIA SYSTEMS θ L Z (about the optical axis) tilt of an array direction cylinder lens will transfer transfer cylinder lens will direction (about axis) array of optical tilt an the aser E mi tt Z ers tilt of a cross-array direction cylinder lens will likely have cylinder lens will a direction of tilt across-array M 66 apped wherein an addressed array of light sources would print would of light sources print array addressed an wherein is described for high-resolution is described printing, electrostatic a calibration process, any outright emitter failures failures emitter any outright process, acalibration
t o
t he M edia 50 µ m, ascomparedwiththe 6 developed cylindrical 81 - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 82 Patent 5,986,819.Patent 3.15 FIGURE for need redundancy. without the undertaken be systems can printing to media-mapped sufficiently emitter robustthat laser are arrays laser diode the that seriously. was taken failure source one case, In arrays, laser imaged directly class use that ofsystemseven simplified this within However, or failure. variability system emitter laser to printing the desensitize to U.S. (From 4,804,975. Patent media. 3.14 FIGURE image setter (shown setter image 3.15), Figure in array, laser addressable an light from collects printing throughput (speed resolution). throughput and printing More recently, proposed it been has cost is provided of atthe alow redundancy emitter The spot. asingleform writing to media onto the is directed array entire the light from the agroup,driven and as An exemplary optical system, exemplary optical An below systems optical motivatedMany discussed of by perceived the are the need
Directly addressed laser array printer with anamorphic optics. (From U.S. (From optics. anamorphic with printer array laser addressed Directly Printer configuration with an addressed laser array imaged directly to the the to directly imaged array laser addressed an with configuration Printer 67 ) La array se r Me dia Rod lens Rod La array Imaging 6 67 optics ) se developed Inc. for an by Scitex Printing Digital Printing lens r 19 the multitude of laser emitters are are multitude of emitters laser the Laser Beam Shaping Applications Shaping Beam Laser La ci Drum contro ser arra rc uitry Me l dia y 67 , 68
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser Helios™ systems Helios™ Polaroid The employ provided sources. diode that laser been of discrete aseries some viable systems modulated, have or indirectly addressed either directly arrays, designs have printer employed thermal laser of high-power many the Although laser m 3.5.2 either systems. of impact these could detrimentally emitters, alight emission emitter, to or as profile emitter fieldfar(near or the field) across output variability, either concern, may adiminishing be array diode alaser across emitters diode laser of the failure outright behavior While source. of the detailed the it sensitive object, and onto is thus the is imaged source to illumination which the in variation. shape and spot size undesired may cause a defocused beam through motion media of the placement. Otherwise, media and drum tight control on the system requires potentially plane, this media at the NA needed cross-array upona defocus the as plane Depending spot width. media atthe width provide to lens desired is rod controlled the the and emitter the of a 20 target the to mapped is be to ter narrow, where the single-mode emit direction, cross-array the In drum. the across have spots of focus depth planes) image object acommon printing and the so that lens is double-telecentric (telecentric both in systems, printing later many the in As µ 20 lens,ing circular arow such that of nominally print a spherical lens and rod system optical a cylindrical with anamorphic vides an consisting of amultitude system of single-mode-by-multimode The pro emitters. U.S. array. (From 6,356,380. Patent of amodulator nonoverlappingadjacent illumination 3.16 FIGURE (not shown). (or acritical system system Nelsonian) is nominally This illumination lens by aprinting media onto the imaged turn, is, in tor array. array modulator The - modula onto the directly elements beam lens optical works the image other to with rod the direction, of adjacentseries cross-array regions array. modulator of the the In one of a illuminates near-field each emitter that images)such array the modulator to (either mapped far-field are emitters laser the projections or direction, array the In alenslet lens including and arod array. micro-optics, employs cross-array and array system, array. light modulator which was developed This tial by Graphics, Barco spa- external an to is mapped source of array diode anonaddressable laser emitters As another alternate system, alternate another As u lt
ip Laser printing system with the laser emitters optically mapped to provide to mapped optically emitters laser the system with printing Laser l e 46 D emitter , 70 La iscre are an example an of of which a design are a series approach in se r s t e Fi L eld lens asers 68 shown in Figure 3.16, shown Figure in diode laser the light from the La M ser arra Rod lens Rod apped Lenslet array µ y m width, the working distance between between distance working the m width,
via F ree Mo - m printing spots is provided. spots m printing dulator arra S pace Me dia O p y t ics 68 83 ) 69 - - -
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 (From U.S.(From 5,161,064. Patent 84 laser diodes.laser of by subpixels,a series acombination of four is written independently modulated pixel each ahalftoning by with writing (256scale levels) Helios modulation. The system grayscale modulation provided the pixels with having gray were 8×10 printed the prints monochrome in. market, ing imag Helios medical initial of the needs quality To image the media. accommodate layerparticle receiver donor between sandwiched and polymer is athreshold sheets, alight-sensitive which comprises Helios the media, media, carbon thermal laser other of many with the As drum. external on an mounted onto spots amedia printing the directs that aprint-head form to combined are beams propagating free-space 3.17 FIGURE emitter lasers, withsingle-mode(~ facet edges. mirror atthe interactions diffractive from variations irradiance with pixel would that originate written the in of overlapoffset and artifacts print reduces well. as combination overlap The but beams some it horizontal has these with also two, first offset the is not from only vertically beam third the not show detail, this 3.17 Figure provided Although be for density highest regions print. the of the does reproduction could tone scale accurate so that beams three other of energy of the the is have to designed beam about smallest one-seventh and fourth offset. The vertical opposite but the with third, the to is positioned and similarly size asmaller spot has the and twofourth butoffset, first spots, the to vertically centered is horizontally elongatedshown, spot two athird elongated offset lie axis, spots along acommon µ overall ×90 90 the within subpixel structure printing each with spots, systemof twoprinting provided configuration opposing facets.four This aunique the betweenthe gap in located mirror 4) tilted a deflects (Laser off beam fourth 1) two the opposinga gap the while facets, between (Laser through passes beam third The 3) paths. 2and parallel into (Lasers two beams laser of the redirect that provides two offset array opposing facets mirror The media. on the spots printing the optics (see 3.18) Figure remaining the through follow paths optical form parallel that were via that combined four beams laser prised The basic HeliosThe system, The fourlaserdiodelasers arehigh-power (500mw)IR(820nm)single-
Printer configuration with a laser array synthesized from free-space lasers. lasers. free-space from synthesized array laser a with configuration Printer 51 La ) 46 ser , 3 70 mirror arra as shown in a simplified form in Figure in Figure 3.17, shown as asimplified form in com 2 Fa ce La La te ser ser d 1 La process in which pixel, each in process consisting of y 4 µ 1 ser m wide,1/e 3 a multifaceted mirror to subsequently to mirror a multifaceted Laser Beam Shaping Applications Shaping Beam Laser 4 2 2 1 NA ~ NA 0.5)-by-multimode m pixels. As - - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 where within the beam shaping optics. beam the where within ~ plane. an aresult, As media atthe equal nearly be two meridians NAs the in the that desired It is also emission direction. the multimode in times three aboutby demagnified ultimately are emitters the while times, three aboutby magnified is ultimately beam shaping, cross-array the such that system optical beam must laser the plane. provide Thus, media adifferential the scan) direction. writing spots across the media relaxes the tolerances in the vertical (or slow timode axis)thaninthevertical direction,becausethescanningmotionof the The telecentricityrequirementismoresevere inthehorizontaldirection(mul - writing beamsareparalleltoeachotheraswellperpendicular tothemedia. to presenttheprintingbeamstelecentricallymedia plane,suchthatthe depth offocusrequiredatthemediaplaneisshort. The systemisalsorequired media plane and able to image the small printing spots. As a consequence, the of subpixel grayscale printing define thissystem to be fast (highNA) at the the collimatorandhada0.47NA. Notably, thecombined systemrequirements ing objective, provided to form thefour spots ontothe media, is a similar lens to long the desiredelongated printingspotsprovided atthemediaplane are~ a fast (NA ~ tems (seeFigure3.18),whicharelargely identicalforthefourlasers,begin with ( subpixel addressing. with spot a printing FIGURE 3.18 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser ~ 100 In this system, the printing spots are formed by imaging the laser emitters onto emitters laser the by formed imaging are spots system, printing the this In ×
µ ~ m, NA ~ collimator 3 Las µ m wide,withthesmallspotbeingonly~
0.55)moldedglassasphericsphericalcollimatinglens.Ultimately, er 1illuminator The Helios optical system from Polaroid, with four beams combined to form form to combined beams four with Polaroid, system from Helios optical The x y 0.07)emissionstructures. The laserbeamshapingopticalsys- + 3elemen z z , ts Las Cylinder 1 er 4 70 (Courtesy of Polaroid.) of (Courtesy Las Las er 2 er 3 8 to 9:1 anamorphism is required some 9:18 to is required anamorphism 100 mm 5 Cylinder 2 × 3µ Au m insize. The focus- tofo cus head 34 µ 85 m - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 greater throughput on larger media. In one generation, In media. on larger throughput greater and features improved with power enabled then designs more printer that and lasers or by facet, its size. reducing 4mirror laser the by masking accomplished be can This path. somewhere optical the must in vignetted be 4 beam (5 size in reduced spot is vs. be to 1–3, of lasers µ that 34 printed the and uniform laser near field than were commercially available. near profiles laser uniform issue this developingby light profiles.ter Polaroidaddressed diodeswith more laser field near emit direction sensitive array printing the to the which makes media, the system uses critical illumination, system critical uses direction array The direction. array the design in optical imaging and direction, propagation cross-emitter design the to applies beam Gaussian anamorphically autofocus Taken an with mechanism. a whole, as equipped be Helios the system the to focusing presented lens, are can which beams collimated final The direction. slow the light in the focusing NA the to (multimode lens, collimate to emission) (single mode) Along positive length, focal direction. closer cylinder lens is located cross-emitter NA the high light in the collimate to array closeis located mirror the to positive length, focal plane. A short media NAs cylinder lens the to printing the ize cylinder lenses, two equal to which comprising crossed is used collimator morphic toward focusing the propagate downstream lens. beams parallel four nominally that sucharray mirror the by redirected are beams The four variations. magnification the systemtherebyilluminator images,to desensitizing emitter final ofsizes the direction fieldarray as act facets the stopscontrolto mirror facets. The array ror mir the ontoimaged nominally emitters imagesthe laser of real magnified the with array, mirror about the radially arranged expander). systems are illumination The classic beam the to (similar element afocal nearly Galilean expanders are beam the imagesthe emitters, of focus that about to 10 magnified output beams times and beams expanders receive collimated beam the As single-mode directions. and the multimode both in emitters imagesthe laser of real intermediate vide magnified systems pro expander. illumination beam These athree-element and collimator the system, optical comprising shaping illumination its own encountered beam beams 86 are used for identical used 100- 4. 4is provided laser laser an As with are (BK-7 SF-1) facet and adjustment angle amirror and asingle while prism is used, positions. in the case of prisms laser of off-axis In 1, a pair collimator cylindrical first length focal 4) short 1and traverse the that (lasers offset beams laser by vertically the needed well as correction, coma wedges as These provide correction, telecentricity wedges. provided prismatic with systems 4are for 1and lasers illumination the and identical, actually are only ones that the systems 3are for 2and mination lasers microlens for the cross-emitter fast axis, formicrolens cross-emitter the (see 3.17).predecessor Figure optics (a cylindrical system, anamorphic the this In systemlater its it is is much cut amonolithic surface, from than easier fabricate to of this mirror multifaced the subpixel As spots. fourels, beam writing the with each pix two form to adjacent writing mirror, about amultifaceted arrayed diodes, laser The HeliosThe system underwent several generationshigher of to use change, first - ana a common travel focusingBefore the four through lens, beams the reaching 3.18, shownAs array, Figure in four of each laser the mirror faceted the to prior While the illumination systems for lasers 1 to 4 are nominally identical, the illu identical, the nominally systems for 4are 1to lasers illumination the While 69 with the source profiles ultimately imaged ontoimaged ultimately profiles source the with 71 and a secondary cylinder lens to correct cylinder lens correct to asecondary and Laser Beam Shaping Applications Shaping Beam Laser 50 the printer comprised eight comprised printer the µ m-wide emitter to to m-wideemitter 50 m), laser the ------Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 collimator, and which works on the fast axis light. Depending upon the design, this design, this upon the Depending light. which works and fastcollimator, on axis the adivergencewith reduction cylinder lens (not shown), the to prior which is located ( NA alow both light with outputs NA alarge emitter and systems, laser the thermal laser the in is typical As of focus depth media. focused the of light atthe the maximize to divergenceas asmall so light with (NA <0.3),limited, likewise finer NA is the and Preferably,the system.output optical fiber to optical the mate to used emits the laser be connector, SMA can such an as connectors, communications optical Standard two-element lens system. output optical by asimilar focused media ontoand the fiber, the optical of andlight fiber is length output light traverses the collected the The unit. laser fiber optical end ofcouplingby a a to an lens fiber form pigtailed focused input onto then the lens and by acollimating is collected diode laser IR an Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser a high-power for source fiber pumping lasers. as applications, and including other setting, image in used been has technology head by atwo-elementfocused media onto objective the lens system. Helios The print- are before eight sizes beams the laser desired the to beams the truncate and redirect both facets before, facets. As mirror the mirror onto the emitters laser ofimages the (48 systems, lenses, provided including magnified spherical completeThe illumination array. mirror the to prior located astigmatism) illuminator, were the designed into lasers. (From U.S. (From 5,351,617. Patent lasers. 3.19 FIGURE simple. one configuration, inherently In anotable being press example. DIHeidelberg printing Quickmaster applications, such CTP, as the with on-press imaging, computer-to-proof, direct and graphics numerous in used successfully been has print-head Presstek This drum. printing of length the optics assembled the ensemble across associated and of lasers an from is formed array extended printing laser An focusand media. light onto the collect to its had own path lasers optical discrete addressed directly ofeach the developed which of in NH) (Hudson, light engines aseries LLC alternative, Presstek an As media. focus to the light to optics used the free-space common of the because but also subpixel of the because structure system acomplex used partly path, optical Helios The heads. printing have assemble to lasers used thermal laser discrete been PolaroidThe Helios which assemblies system in of example is an of printer alaser a 3.5.3 This approach has the virtue that the laser beam shaping optical systems are systems shaping optical are beam laser the that virtue the approach has This and 6.6 × and > 0.3). To equipped input be fibersystem also optical the could compensate, rray
× , respectively, directions) real cross-emitter and for multimode the Printer configuration with a synthesized laser array having having fiber-coupled array laser a synthesized with configuration Printer P rin t ing Collimato La
wi se r t h D Coupling lens 17 r ) iscre Optical fiber Optical t e 17 L as shown in Figure 3.19, shown as Figure in light from the aser 72 , 73 O p t ica l Drum S ys t ems 87 Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 annular bafflewithinthefiberoutputoptics systems. optical laser individual of the following the in discussed section) calibration fabrication and but upon the depend print-headreference with one mechanical the notwithfiber defined pigtailed (as are array,distances the laser as focal the controlto synthesized difficult across focus Similarly, be it over can drum. of length the the systems maintained optical being of adjacent series the laser between tolerances alignment optomechanical on the is moved print-head the laterally. and system is rotated The places apremium drum the as sible drum, of its the respective its pixels portion image for within printing system optical laser is respon Each drum. of length the systems the optical across fiber. optical an into than rather media, haveto the ontoinput the lightdirectly optics configured the system be focus can laser, the the optical reflection-induced in or mode bending hopping noise fiber from fiber, avoidto by optical anyas coupling the to as optical well light loss the incurred ~ between spots printed produce can printer 88 technology. (Courtesy of Presstek LLC, Hudson, NH.) Hudson, LLC, oftechnology. Presstek (Courtesy 3.20 FIGURE pixels areprinted,thereby improving theimagequality. in themultimodelightthatemerge fromtheopticalfibersothatmoreuniformimage controlled angle diffuser can be insertedprior to the baffle to smooth outhot spots focus losscausedbyhigh-NA lightemerging fromtheopticalfiber.a Inaddition, the beamLagrangeispresumablyincreased. As previously noted, this systemcanbe multimode lightpeakscanalsoimprove thedepthoffocustomediaplane,although Further improvements have beenmadetothisapproach,includingtheuseofan of laser aseries is achieved by printer arraying 3.20, shownAs Figure in afull
A digital offset printing press using Presstek’s laser thermal imaging head head imaging Presstek’s using thermal press laser printing offset A digital 12.5 40 to limit ghost reflections and depth of tolimitghostreflectionsanddepthof µ m and 50 µ m and Laser Beam Shaping Applications Shaping Beam Laser 41 Smoothing out of the sharp Smoothingoutofthesharp m in size. Alternatively,m in - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 addressed IR laser acting as a pump laser to an external laser crystal. laser external an to laser apump as acting laser IR addressed conjugate distances(fibertofocusinglensthedrum)arebeingchanged. working distance,althoughasmallvariation intheprintingspotsizemayresult, asthe this approach,thefocalpositionforeachchannelcanbetunedtoreachneeded Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser ple, alow-NA produces single-mode TEM which may aNd:YAG be crystal, laser The crystal. face laser of the for exam crystal, focusing aspherical lens,tion which and together end light onto focus pump the the provided microlens for divergence acylindrical light encounters laser pump - reduc plate printing. system provides This channels. 21 µ by a the media singleontoimaged assembly lens then fibers is provide to writing four µ a 60 ing fiber, optical hav coupled is optically acorresponding to emitter laser Each beams. provides that four uniquely laser addressable array diode a laser and driver board alaser containing each sources, diode laser of which IR aseries uses name, trade to minimize printing spot size variation. spot size printing minimize to order in crystal of mounting the mechanical and thermal the optimize to and spots, printing of shape the control to the width pulse the for optimizing crystal, laser the of time response the enhance to light available made also Provisions for are printing. wavelengthin conversion, of the brightness in overall thereby providing increase an for power compensates the more than lost source, pump original the with compared by afocusing media divergence,on the objective beam the reduction in lens. The media plane, an alternative, highly integrated optical fiber print-head fiberdeveloped print-head was optical integrated alternative, highly plane, an media the to directly mapped systems, prior of many to having emitters the laser Compared f 3.5.4 optical systems another, provision hasbeenmadetoindividually shimeachoftherespective output drum. To address this variability of the spot focus from one laser optical system to variations inthelaseropticalsystemsandmisalignmentofprintingheadto sensitive tofocusvariations acrosstheprintinghead,whichcanbecausedbyboth U.S. (From 5,822,345. Patent EO-crystals. 3.21 FIGURE A novel system, 3.21, shown as Figure design in this to alternative directly the has Presstek developed technology,Presstek print-head another i m core and a 0.12 and m core of group each four light NA.output optical from The b er
A Printer configuration with a synthesized laser array using IR laser-pumped laser-pumped IR using array laser a synthesized with configuration Printer 74 rray inordertoadjustthefocusingdistanceoutofeachassembly. With P La + se rin r Cylinder t - lens H ead Objectiv m laser spots to the media, enabling 2540 dpi 2540 enabling media, the to spots m laser lens 75 ) e 00 Cr 1064 nm output beam, which is focused output beam, 1064 nm ysta Fo lD cusin lens 45 g branded under the ProFire ProFire the under branded ru m 75 The 808 nm nm 808 The 89 - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 efficiencyto ~ the system reduced light both print-head the fibers diodesto laser fiber pigtailed the or by simultaneously. doing both lines, scan the Unfortunately, fusion coupling of the or by print-head interleaving the by tilting increased further could be print-head the of output µ end 20 with the reached structures, 250 250 input V-groove end with at the cement. The curing ultraviolet started base (UV) ST connectors, which haveST connectors, positioning the accuracy. ahigh enhance To further fibers optical print-head the into (also NA ~ NA with ~ beam Gaussian a generally light, ~ 0.24 NA fiber supports 0.24)with ~ lasers yield to fiber pigtailed (NA ~ fibers optical multimode individual lens the into is coupled by acylindrical light output single-mode-by-multimode that power This light. emitters laser 830 nm of high- array V-groove an comprises system. source laser diode Each printing an excellent job of simulating the halftone printing process. excellent printing an halftone job the of simulating does technology resolution writing of thermal high laser tone scale. The the create to more or less ink by on apress may replicated imprinting be process This black inks. yellow, using on apress cyan, magenta, printed stock. Colorpaper are images and yellow, to customer the laminates that sheet black and dyes intermediate onto an cyan, magenta, image to technology systems thermal laser use These diodes. laser replaceable provides with head print-head individual acompactSystem. optical This Company for KODAK Kodak the by Eastman APPROVAL Color Digital Proofing 90 coupled laser diodes and aV-groove and (From diodes U.S.4,911,526. mount. Patent fiber laser coupled 3.22 FIGURE printing uniformity. improveto added were channels and dummy fibers, optical multimode and lasers fibers with single-mode multimode replaced optical and were single-mode lasers except the architecture, versions, asimilar uses 64-channel and built-in 30-channel V-grooves, which were etched 18 amere to µ progressively are fibers µ 125 initial the fromdown etched spots. of printing lens provide to array by aprint an media aged onto the of adjacent V-grooves.brought apattern together in fiber The exit faces reim were fibers single-mode optical (5 µ print-head corresponding to individually spliced diode lasers coupled fiber pigtailed The APPROVALThe Color Digital System Proofing print-head, The first fiber array print-head printer print-head array fiber first The In order to reduce the spot pitch (increase the optical fill factor), fill optical spot pitchthe the optical the (increase reduce to order In µ m pitch V-grooves of progressively aseries through V-groove and, smaller
10 m diameter. The reduced optical fibers were then assembledthe fibers then into optical were reduced m diameter. The Printer configuration with a laser array synthesized from discrete fiber- discrete from synthesized array laser a with configuration Printer and caused channel output power channel caused % and instability. Cooling 33 blo Dio , 35 ck Figure 3.22 Figure shows of afiber path asketch optical of the de la sers 90 76 m core), fibers optical were print-head where the , 77 % O into crystalline silicon, and held place and with silicon, in crystalline into of the coupled optical power is contained within coupled within of power the optical is contained fibers ptica 0.12. The pigtailed optical fibers are coupled are fibers 0.12. optical pigtailed The l 18 , 32 400 mW400 fiber. output per the Although m pitch V-grooves. factor fill optical The , 37 V- 0.24) by means of standard industry industry 0.24) of by standard means was developed of using butt- aseries mount gr oove Laser Beam Shaping Applications Shaping Beam Laser Printing lens m diameter cladding, m diameter 33 , 78 which has been been has which 18 ) - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser silicon fibers print-head (52 µ have can fibers core coupling reliability, a smaller pigtailed (50 the 3.23 FIGURE [fiber ( array Laser mode hopping, which is of direct or indirect lasing cause instability, can hopping, mode or indirect Laser which is of direct and so on. the path, in bends sharp crimps, result ofirregularities, fiber-to-fiber the higher-order into as modes scattered be modes.order Likewise, can energy higher-lightinto launch can drum traversesthe print-head the as ment fibers of the media. print on the spots writing of the focus optimal ensure to used be proof. autofocus can on the An mechanism direction fast scan the to delayed normal pixels digitally aline to align to are channel each data for The lens magnification. for in compensates variations array of angle the the spot-to-spot achieve spacing. to Adjusting desired is tilted the array The directions. cross-array and along-array the spot-to-spot both spacing, the in can as measured, nification, the print lens print the nification, mag ata therebymodest As and is it operates lens, clipped. print the light overfilled NA fiber atthe of higher-order,0.12,the acceptance that resultan the with large NA one lens version had In over system, printing ofis mounted the the intermediate. the the donor 2.2:1, where of drum, a demagnification the of array onto fibers the images array. exit at lens, fiber the working printing A light beams printing which the from 3.23,shown output Figure surface in provide coplanar to is polished and asmooth the gaps between the optical fibercores. optical gaps the between the resolution print-head apparent for by the compensating increase to angle acute an at tilted be could also print-head This drum. is moved the head across the laterally as pattern spiral helix along a nominal swaths of data lens, image writes print the assembled V-groove the NA). comprising print-head, and integrated array fiberThe The multimode print-head optical fibers are glued intoglued are fibers optical print-head V-groovesin multimode etched The As might be expected, this system is sensitive this expected, be might As fiber to 76 , 77 at130 µ ~
2 mm fieldand ~ 2 mm Portion of the end face of face array. end aV-groove of the fiber Portion optical m spacing between centers. The end face V-grooves, of The the centers. between m spacing as m). 79 supports relatively supports the object fields large and both at NAs 0.12 NA)] ( planes image and 34 The fiber-to-fiber be can The error placement noise. For example, move ~ 1 mm fieldand ~ 1 mm µ m) than the m) the than 0.264 0.264 91 - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 addressable laserdiodearray(IALDA) coupledtoafiberarray. Asan CreoScitex Corporationdeveloped asystem prints and making them less noticeable. them making and prints the in artifacts up the of breaking method is another data image with laser of the Modulation artifacts. of these appearance up the position. break Additional channels power, optical temperature, by wavelength, laser diode changes in or mechanical caused transients aresult of as startup laser exhibit channel artifacts single can laser using a noise. created channel Images individual the reduce further source laser each multiple noise elements The random source. laser constitute diode that uncorrelated may considered sensitivity noise, an be laser channel each the as individual to reduce axis (FA)axis lens on one side slow and (SA) axis other. on the shown lenslet As array versioncustomized monolithic fiber-coupling of LIMO havinglens, common a fast tion becauseofthelimitedredundancy andrelatively high costofservice. emitters, printers that use direct imaging ofIALDAs found only modestimplementa- the imaging side, as illustrated in Figure 3.24. Despite having a provision for spare provides two-fiber alignment V-groove assemblies,oneattheIALDA sideandoneat bundle ofoptical fiberstoanoutputoptical bundle viaaconnectorboard,andfurther addressable laseremitteriscoupledtoanopticalfiber. The print-headroutesaninput ping, changing the output power the ping, wavelength. changing and hop cause diodemode laser the to reflections laser.returning diode the to Optical uniformity. print final the affecting variable, potentially spots printing the within light profiles the make Finally, also higher-order can modes noisy or time-variant system the sensitivity of increase focusfocusto depth thus position.and a smaller NA large provide they modes, typically higher-order are modes the as Furthermore, image. the within trace line adifferent in resulting spot, the within structure the changes and noise rotates problematic interactive. be ping, and can Mode structure power) plane. media the to through ( [NA lens with a printing faster modes. Alternately, configured system be the can 0.12 remove to original vignetting higher-order unstable lens used NA these print light efficiency, cost At of the areduced is attenuated. notmodes automatically the tivelythoseinto light fiber large that launched NA systemthis (0.24) means in used rela NA- the high light, comprise effects. higher-order typically As modes similar 92 ratio of the print-head cost to total system 20 cost cost total is to less print-head of than ratio the the because reasonable is a compromise channels About 30 fiber pigtailed increases. grows of number also channels rapidly print-head the as the cost support to tronics excessively becomes head elec- expensive The increases. of number channels the as print- laser cost fiber of pigtailed the total the 3.5.4 straightforward, is technically previousin Section described print-head multichannel fiber pigtailed the Although f 3.5.5 ~ 0.48) plane] media allowed the to that most higher-order-mode of the light (and One approach to reduce the cost of the fiber array head is to use an Notably, however, a used print-head coupling, this array fiber to for array laser Laser mode hopping can be minimized with careful coupling of the optical fiber optical coupling of the careful with minimized be hopping mode can Laser fiber movement from whether orhop structure, mode mode Noise higher from i b er A rray P rin t - H ead
wi t h A ddressa 81 Laser Beam Shaping Applications Shaping Beam Laser inwhicheachindependently 80 bl Multiple channels laser diode e L aser A % . rrays individually example, - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser tem to provide source redundancy without resorting to an external modulator array. modulator external an to without resorting provide to tem redundancy source array, diode laser whichaddressable provided subarrays, allows laser with sys the - it adirectly is uses that print-head monolithic multichannel of the keyThe attribute o 3.6.1 Screen. Dainippon and Matsushita systems by setting both image Company, dry Kodak in used by been has Eastman for which was of reliability. developed print-head, emitters redundancy This and power optical one gain spot into to lasers single-mode of diode group each these overlap to from multiple pupil reimaging spot and beams and microlensletthe arrays substrate. same on the is provided multiple with of array groups lasers single-mode addressable laser diode was developed which the in architecture aprint-head cost, print-head the reducing to approach alternative emitter. an As afailed substitution laser correct to require thus lack provided redundancy, pixel to both they laser both as they addressing, emitters, fiber-coupled with system array the laser addressable 3.24, ofand Figure an with system the 3.22, ofAlthough Figure multiple with fiber-coupled individually lasers, 3.6 10 approximately be to meant is then SA the direction in spot size the and directions, both in SA position. fiber atthe The lensequal coinciding be exit to intended NA is or direction or FA array of plane focal cross-array the of plane the image lens the and the with views anamorphic, lens cross-sectional is highly 3.24, of the Figure in this views. sectional 3.24 FIGURE smaller than the fiber core diameter. fiber core the than % smaller The associated optical system optical associated The
MODULATED SUBARRAY LASER PRINTING LASER SUBARRAY MODULATED p t La
ica Individually addressable ser diode Anamorphic monolithic array and cross-array lens, perspective and cross- and perspective lens, cross-array and array monolithic Anamorphic ba l C r Fa onfigura emitters st ax 58 Common FA , 82 is t ion lens 7,
82 of provides a sophisticated design that employs provides design that asophisticated
a M SA lenses ono l i t hic Slow ax M u Fi is lt be as ichanne rs V- sembly gr oove l P rin t - H ead 93 Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 ceases to emit, the others can compensate the power the compensate loss can by others their slightly the increasing emit, to ceases power reliability. in degrades or laser asingle-mode increases diode If lasers diode laser. amultimode behaves like optically channel each incoherent, mutually are 16 achannel the within single-mode lasers 16 Because all channel. is overlap spot of that single-mode their lasers printing atthe power, whileintroducing areasonableopticalsystemcomplexity. Another requirement to nearly factor fill the 100 increase to 250 by 10 into separated 835 which gathered or subarrays, are lasers groups diode nm factor of the laser array is very low is very ( factor array laser of the is ~ array the in lasers single-mode of diode the of length all total at50 µ spaced 94 The optical layout, optical The U.S. (From 5,619,245. Patent subarrays. 3.26 FIGURE 3.25 FIGURE imaged to the media. the to imaged are beams ensemble the of and printing beam, aprinting into rays collected are subar addressed of each the from respective which beams the concept in imaging intermediate employs direction direction, array 3.26Figure an for cross-array the rays. (From U.S.rays. (From 5,619,245. Patent In additiontoopticalpower gain foreachchannel,overlapping ofthe16 The laser diode array diode laser The µ m spacings. Each channel, which is composed of which is composed m spacings.16 channel, Each lasers single-mode diode Las Collimator lensle
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Emitters er array m intervals, is 750m intervals, µ barr Array direction optics of a laser printer with addressed laser emitter subar emitter laser addressed with printer of a laser optics direction Array Cross-array direction optics of a laser printer with addressed laser emitter emitter laser addressed with printer of alaser optics direction Cross-array o esCollimatorlensletarray lens Rod ay Rod lens Rod 7, 14 , 57 shown in Figure 3.25 for the along-array direction and in in and 3.25 shown Figure for in direction along-array the 58 Cylinder t , 82 that powers this system powers 160 that comprises this single-mode, Combiner lenslet 57 ) Las m wide and driven by driver.m wide and its own current The Combiner lensletarray 57 er spot ~ ) Cylinder on the medium without losing medium much% on the optical 6 % Fi ), challenge system of the optical design is eld lensle Fi eld lens Wa Stop is ts t Laser Beam Shaping Applications Shaping Beam Laser Printing lens Me Stop Printing lens di a 10 mm. As the fill fill 10 the As mm. Me Printing spot dia single-mode single-mode - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 is remedied problem This channels. central but the not channels affect laser outermost of the stop, aslightthat stop misplacement of and would that severely atleast one vignette combiner lenslets would onto beam of projected images the be of separated a line fieldthen only lens. this lens is used, If stop printing of the aperture the through pass they that so beams the diverts image plane intermediate theA spots. field near lens printing of addressed provide to plane array an media the to directly spots laser the specifications. Most simply,printing provided be could reimage lens to printing a However,spots. spot pitch the may incompatible and be spot size the with the both ensembleNA the of from 16 is arelatively beams laser ~ large given emitter has a miniscule NA ( aminiscule given has emitter a although aresult, As beam. combiner lenslet Gaussian of acombined the forms and ensembletivethe aperture the of combiner lenslet 16 total, fills in such that, beams - respec of the input aperture the into directed are beams 16 the Note that collimated magnify a~ magnify µ lenslet, of length afocal 200 with acollimator and of length a focal 50 mm, combination of plane. image The acombiner lenslet with intermediate an to trically telecen nominally presented which spots, are laser imaged available as downstream overlapping in (channels) subarray laser beams fashion, 10 such that separated are agiven from subarray. beams combiner lenslets The focus respective collimated the (the combiner lensletarray array) is provided one with combiner lenslet laser per 3.25 Figure for in depicted clarity. are channel each lenslet in A second emitters lenslet. two by 16 Only of acollimator the agiven is collimated in subarray laser 16 of each the emitters detail, laser without image loss greater the of In brightness. conjugation, pupil-to-pupil with object-to-image conjugation, obtain to intertwined system optical employs direction array aclassical design approach of optical The field the media. to beams combiner)(or of the channels and gather collect to lenses Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser improvedresult.as a significantly power. robustness are systememitted and print-head multichannel reliability The NA of each beam from the diode lasers in cross-array direction. The optical system optical The direction. cross-array in lasers diode the from NA of beam each the reduces rod The lens rod the lens. by collected is first lasers single-mode diode the light from plane. The media atthe lens, and stop printing of the aperture the near but spot images, laser fall to coincident be to not the with formed are waists beam Gaussian beams. of the but, shape nominally,to cylinder lenses is used a variety media. the to of arow such one-fortieth that of µ 25 ( is high plane media the factor at fill lightthe optical the given of a by spot, filled mm laser 1 is nominally each as field and, field lenslet the lensthe medium images onto array lensletprinting the aresult, As channels. of for the all vignetting the lens, equalizing printing of the stop atthe lenslet’s others of the onto all the combiner superimposed be to images field context, the stop. this each causes lens of In occupied by aperture plane the lenslets ofEach these effectively combiner lenslet the to a corresponding reimages The print media can be colocated at the image plane occupied by the imaged laser laser occupied by imaged plane image the atthe colocated be can media print The In the array direction, the print-head the direction, array the In The cross-array optics, shown in Figure 3.26, can be configured in numerous in numerous ways optics, configured 3.26, shown be Figure can in cross-array The 57 4- with the addition of another lenslet addition of another the array, with consisting of field lenslets. µ m-wide by ~ emitter ~ 100 % ). The print lens reduces the spot size at a magnification atamagnification spot size the lens reduces ). print The ~ 0.1/250) composite the spots, laser imaged atthe 250 times to an ~ an to 250 times 7, m printing spots is presented telecentrically telecentrically is presented spots m printing 57 uses a series of refractive aseries uses lenslet and arrays 1-mm-wide spot). (laser image 0.1. m, is to m, 95 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 the mediaplane. laser spotimages,toprovide adramaticincreaseintheeffective depthoffocusat with asmilecorrector, and contaminationofopticalsurfaces bydirt. This systemcanalsobeoutfitted losses, suchasexcessive lossinthecombininglensletarray, opticalmisalignment, implying that about 10% calculation suggeststhatthesystemopticalefficiency shouldbeabout80%‒85% to image-recordingmediumisapproximately70% the writtenmedium. the diodelasers,andatfocalplaneintendedtobecoincidentwithsurface of is measuredforeachchannelofanarraybothatthecombiningplane,50mmfrom diode laserarrayinsidetheenclosure,opticalpower vs.current system spot. around produces a three-cylinder whereas a2:1 spot with elliptical media, an on produces ratio the aspect direction cross-array the two-cylinder lens system Ain directions. cross-array and array the ficationsin relative the to magni according spot, elliptical spot either form or an around can 96 these developments by Xerox, modulator array/laser array printing systems developments havethese printing been by array Xerox, array/laser modulator plane. Subsequent media array, to the modulator to and the array, laser through the from lighttechnology, transfer to basic systemtor array the optical configurations and which developed acomplete aviable solution- sources, modula including array laser market. arts developed been for graphic for plate the applications, setters including various CTP have of number alarge channels with print-heads thermal laser decades, recent In 3.7 print-head can typically deliver typically 12 can print-head of array, plane. For which media type example, is subsequently the to this imaged light modulator a spatial light illuminates wherein laser print-head integrated an uses lower that to velocity. direction print-head print-head the velocity wellhead as reverse to less as acceleration exposing time, while media, the allows print-head the a in lowersetter, plate providinga flatbed more channels print- lower that to In r/min. drum the decelerate and accelerate to less time and media, the exposing while alower means drum of the this r/min drum, on arotating mounted slower. be relative can print-head of medium the the speed of to case media the In productivity, the printer thus same and the maintain to channel each from needed upon the properties of the spatial light modulator array. light modulator spatial of the properties upon the of such systems dependent is very performance design and The illumination. beam of laser acontinuous line derived from are they stitch because seamlessly channels previously. discussed system writing advantage, the additional architectures an As (e.g.,of channels high-power writing 256 channels) more cost effectively the than delivers number also large the design architecture array. laser monolithic diode This the from of and about 6W 10coupled fiber atotal to optically the lasers Wfrom After the fiber lens andcombininglenslet array are alignedwith themonolithic The preferred system architecture to achieve a large number of printing channels channels achieve to of number alarge printing system preferred architecture The This design space was first design was space first extensivelyThis developed by Xerox Corporation,
LASER ARRAYLASER AND MODULATOR ARRAY SYSTEMS 22 In general, the more channels in a print-head, the less power laser the aprint-head, in more channels the general, In 83 The typicalefficiency oftheopticalsystemfromdiodelaser 62 additional loss is observed. There are several unaccounted positionedbetweenthecombinerlensletarrayand ‒ 25 W of optical power to the media, compared compared power Wof25 optical media, the to Laser Beam Shaping Applications Shaping Beam Laser fortheprint-head. Theoretical 84 – 86 - ,
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 by Kodak Polychromeby Kodak Graphics™) for newspaper printing. is typically either lithium niobate (LiNbO niobate either lithium is typically substrate, which the electro-optical fieldsvoltagepenetrate electrical The is applied. fieldsfringe when electrical polarity alternating of provideto a structure fingers interlaced as formed are patterns electrode substrate. The electro-optic of an top surface on of the adjacent electrodes row patterns of pixels individual as formed plate setter plate Trendsetter Creo thermal includingdeveloped products, the in used and by others, FIGURE 3.27 FIGURE (TIR) modulator, reflectance internal by system Xerox applications. is enabled This by total for the printing electrostatic ( of having number alarge channels array light modulator aspatial with array diode or laser alaser system combined that printing early An 3.7.1 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser hc a easgiiatipdmn oteotmcaia ytm design. which canbeasignificantimpedimenttotheoptomechanical system requires thelighttoattaingrazingincidence in theregion underneath the missive device, whichisgenerallyadvantageous, optimaloperationofthe stops) as side lobe interactions were reduced. Although the TIR modulator is a trans - best resultswereobtainedwith Gaussian apodized stops (rather than square laser sources(HeNelasers)andimagingofthelightdiffracted aroundthestop, array isimagedtothemediaplane. As theinitialXeroxsystems the meanstofurnishanaddressablearrayofpixels whenthespatiallightmodulator of themodulatedandunmodulatedlight,thisSchlieren-typeopticalsystemprovides drive voltages increase. to required the caused substrate the and electrodes gap the between air ofpresence an of number alarge pixels, the for realizing means easy approach provided an this were bythat proximity-coupled contact provided driver chip silicon electrodes multichannel with aspecial but rather strate, sub electro-optic on the directly not did employ modulator patterned TIR electrodes laser diode arrays, micro-optics, and spatial light modulator arrays. light modulator spatial and micro-optics, arrays, diode laser were enabled including for by improvements, technology numerous areas, various in directed to a Fourier plane within the printing lens. The initial versions initial lens. The printing the within plane aFourier to directed light is when the patterns diffraction result in turn, which, in light beam, transiting the to imparted are differences of Phase refraction. indices the changes in localized When properspatialfilteringisappliedtodiscriminatebetweenthelightpatterns T he 9 and the KODAK the and TH180 System NEWSETTER Platesetter (developed X
ero The linear TIR spatial light modulator. light spatial TIR linear The x T O be ptical IR M am odu l a t or 87 A , 88 rray with the electro-optic substrate. Although substrate. Although electro-optic the with shown in Figure 3.27, shown Figure in an which comprised Ele 3 ) or lithium tantalate (LiTaO tantalate ) or lithium ct ro S des ys t em Pi xe Pi Su l xe bstr l Angl surface at > e 10 ed 5000) was developed5000) These later systems later These 85,86 usedcoherent 3 ), produce to electrodes, 84 modulator , 85 of the of the profile 97 - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 an in-lineopticalsystemconfiguration. 98 As shown inFigure3.27,theinputandexit faces canbecutatanangle, FIGURE 3.28 modulator array. In the cases where a Gaussian beam laser source is used, source laser where beam aGaussian cases array.modulator the In system, focus to the light to optical used the cross-array anamorphic three-element modulator, a the light to and expander, present to collimated beam used direction array an system comprised modulator) adivergent illumination and The direction. of the direction array (aligned the to meridian acollimated with a single beam, outputs source laser unspecified The optics media. couple to print light onto the shaping optics, sheet beam laser system, including anamorphic of printing type this optimize to ments required modulation contrast overmodulation contrast throughput. optical system such, emphasizes As this media. the to imaged be light can diffracted order higher- the light so that diffracted direction array stop blocks zero-order the central a costthe few butpercent, within profileto at of a 50 light spatial the uniformize to apodizer, an with system equipped could be mination lack a common phase and can be combined without interference. The beams were beams without The combined interference. be can and phase lack acommon avoid to enough apart far locking, they phase are emitters laser resulting the As pitch, out but same one row of other. 90° from atthe phase the to spaced emitters rows, two the parallel in with located are emitters the wherein emitters, laser mode closelyAccordingly, comprising array diode packed single- alaser Xerox described light must sufficientlylaser incoherent be fringes.to avoid interference significant the of In particular, system.type this of performance actual the to significantly utes array.contrib the coherence modulator Laser thereof) the lack (or flood-illuminate to is used multitude of emitters laser the where light from light source the as array The XeroxThe system, As an alternative, an As The portion. lens imaging an and afield lens comprised portion lens printing The
La The Xerox printing system with TIR modulator array. (From US 4,591,260. array. (From modulator TIR system with Xerox printing The Be se illuminatio r am expander “She 8 Xerox developed also asystem diode alaser uses concept that 85 TIR modulator , 86 et Rod lens Rod , ” 89 Ap illumination to the modulator array, and imaging array, modulator imaging and the to illumination line or n shown in Figure 3.28, introduces many of the basic of many 3.28, shown the ele Figure introduces in er ture Image signal Sc hlieren imag Fi Central stop eld lens Laser Beam Shaping Applications Shaping Beam Laser light loss. % light Imaging lens Imaging ing optics statio Print n 85 86 toenable the illu the 89 - - - ) Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 other modulator technologies, modulator includingother absorptive devices, Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser wide variety ofmodulatortechnologies.Inactuality, theappliedpower densities, a laser array) andaspatial light modulatorarray, would seem readily adapted to a This laserthermalprinterdesignarchitecture,whichcombinesasource(often s 3.7.2 array. modulator atthe distribution illumination Gaussian a optics,produce to generally field, far anywithout the uniformizing in combined device technologiesincludepolarizationmodulators(suchasPLZT), technologies have potentialandhave beenappliedinprintingsystems. Candidate favors alinearmodulatorarray. Despitetheselimitations,several laser diodearrayandtheswath printingmotionoftheprint-headrelative tothemedia) consideration. Moreover, thegenerallineararrangementofsystem(including choices, therebyeliminatingLCDarraysandmany micromechanicalshuttersfrom geometry, andmodulation speedrequirementsoftenlimitthedevice technology also provide a minimum contrast ratio of ratio ~ contrast providealso aminimum pixel upon modulator factor, size,and fill efficiency. optical modulator The must digital mirrorarraymodulators(DMDs), of the Schlieren-type modulators. Schlieren-type of the modulation performance the affect light can laser emitted of coherence the of partial system and efficiency. modulation contrast between tradeoff degree the addition, In inherent an creates also and stop may plane required, be internal an to lens, access as designthe printing the of impacts turn in filter design angular design. of The the filter angular the upon depends the modulation of The quality downstream. filtering plane or Fourier angular require incident and light, the modulation to phase impart by the system. Furthermore, to enhance the uniformity of the response across the the across response of the uniformity the enhance to by system. the Furthermore, supported Lagrange direction etc.) array the crosstalk, may determine minimal trast, allowed (modulation the response NA and for con optimal array modulator of the length the direction, designs. optical For example, array the cross-array in and array tors, sity of about 1kW/cm power beam den alaser must able and be dently sustain to channels, addressable or more indepen 200 explicitly. needs typically array light modulator spatial The based, suchthatamoderate(10‒25:1)dynamicrangeisoftensufficient. on thetypicalgraphicsartmediaisquitelow andisthresholdratherthangrayscale- applications thatemploy modulatorarrays,themodulationcontrastrequiredtoprint light that is modulated to the the to is modulated light that incidence, which incident either absorbs the device,a transmissive atnormal used ~ should less be than times fall and rise beam modulated addition, In 980 nm. wavelengths, and 800 between typically off channel the However, most viable of the modulators Potentially, optimization of the modulator performance can also limit both the the both limit also can performance Potentially, modulator of the optimization The specifications on the spatial light modulator array can be consideredbe more can array light modulator the spatial on specifications The From the optical designer’s would optical From be the array modulator optimal perspective, the 94–96 andelectro-opticgratingmodulators. pa t ia l irradiance), and work and well irradiance), atsemiconductor, source bar laser diode L igh t 2 M . This laser beam power density is rather high, and depends depends power and high, beam density laser is rather . This odu l off a t 99 ors state or reflects or reflects lightit state backtoward the source. In lower In power systems applications, optical and 2 µ sec. 87 , 10:1 (the on of ratio channel 88 92,93 , 94 – 84,87,88,97,98 98 micromechanicalgratingmodula- are Schlieren-type devices, which which devices, Schlieren-type are Comparedwithmany other 100 may also be viable. be may also modulator array irradiance to to irradiance 90,91 AOMs, 99 - - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 that a spatial light modulator array needs uniform illumination. uniform needs array light modulator aspatial that instance the in particularly printing, extendable thermal laser are approaches into by fly’s uniform made been has lamps design These eyelight integrators. or pipe excimerdesigns have YAG light from where lasers, the used been or arc lasers, a 3.7.3 tolerated. of smile laser amount including the systemmay impose constraints, pixel the extent and characteristics response modulator the direction, cross-array the incident Similarly, light. oriented in telecentrically and uniform spatially lator with modu present to the shaping optics may required be beam array, laser modulator the 100 array. (From U.S.array. (From 5,923,475. Patent 3.29 FIGURE circuits, of integrated example, printing photolithographic the in For illumination. providing uniform while brightness the preserve substantially or fly’sto in applications where it is necessary appropriate is eyeoften integrators cavities, of bars) use integrating either light pipes and (integrating diffusers use that including considered, those could be uniformity formethods illumination improving of array. modulator avariety the to Although (pixel pixel) to illumination the and array modulator the of of response both uniformity is dependent upon the quality system employs that aprinting print array, resulting light modulator In the aspatial the brightness of the laser diode array source (less transmission and other losses), other losses), and (less transmission source array diode laser of the brightness the largely while preserving radiance, of light of along, with uniform line narrow array modulator the optics illuminate cross-array and array pixels. the addition, lating In activedefined the heightto modu the of corresponding width anarrow within fined modulator, waist atthe which is is focused con abeam form to emitter each from light the direction, cross-array the In light. uniform with array light modulator spatial a illuminating flood to contributes systemtion optical of micro-optics, optics and fly’s the integrator).- particular, In direc array eyeintegrator,the of portion which is a optics (the conjugation)to-pupil fly’s illumination light integration traditional and eye (object-to-image techniques optical classicalbines conjugation imaging pupil- with 3.29.shown Figure in Company, developed Kodak print-head, The by com Eastman is means array, light modulator light uniformization and a spatial light source, array One exemplary laser thermal printing system printing exemplary thermal laser One Combiner field lens Las n Uniformizer 1 lensletarray A er diode array er diode
rray Laser printer using fly’s eye optical integration to illuminate a modulator a modulator fly’s using illuminate to printer integration Laser eye optical P Fi rin eld lens t - Rod lens Rod H Uniformizer 2 lensletarray ead Las 11 er lensletarray
) wi t h
a F l y ’ s Fi E eld lens ye 10 Laser Beam Shaping Applications Shaping Beam Laser I , 11 n , 102 t egra that combines a laser diode diode combines alaser that Mo Cros dulator arra t or s- array lens Imaging lens Imaging Fi eld lens 101 amultitude of y - - - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 improved points oneachofthesources(emitters).However, ifthenear-field laseruniformityis is incompleteinthatallpointswithintheilluminatedareadonotseelightfrom such effects areaveraged. Putanotherway, thelightintegration throughthefirststage the emitters,suchasedgeroll-off shown inFigure3.6,arenotremoved, although angularly orspatially. As aresult,any systematicproblemsinthelightprofileacross b are shown asfollows: planesa the modulatorarray. For clarification,theimageconjugate relationshipsinthesystem ter intoN is designedtouniformlyilluminatethemodulatorbydividing thelightfromeachemit- includes thetwo uniformizerlensletarraysandtheimmediatelyadjacentfieldlenses, length ofthemodulatorarrayisilluminated.Ingeneral,fly’s eye integrator, which to collectlightfromeachlaseremitter, andmagnifyredirectitsuchthattheentire field lenses,andtwo uniformizerlenslets),asillustratedinFigures3.29and3.30,is direction illuminationoptics(thelaserlensletarray, thecombinerfieldlens,several systems designed for the array and cross-array directions. The operation of the array uses largely anamorphic(cylindrical) laserbeamshapingoptics,withseparateoptical lens, appropriate. as printing of the vicinity the positionedbe in would means filtering the type, or aSchlieren type polarization such as used, of array modulator type upon the Depending spots. packed writing of closely aline lens create to by print plane the media the to telecentrically imaged is modulator illuminated relativeThe emitters. providing redundancy the to and FIGURE 3.30 FIGURE planea mination to image thebeamsfromeachemitterinoverlapping fashion toanintermediateillu- integration, thelaserlenslet array is used in combination withthe combiner fieldlens corresponds tothebackfocalplaneoflaserlensletarray. As afirststageoflight Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser has beenoverlapped atthea corresponding toagiven laseremitter. Although thelightfromvarious emitters 0 andb As withmany oftheotherlaserthermalprintingsystems,systemFigure3.29 1 a . Planea 2 50 0 multiplebeams. These N consistently, theuniformizationopticscouldbeproven unnecessary.
Las Light transfer within the fly’s the system. within optical eye transfer integrator Light b er diode array er diode 1 0 . The laserlensletarrayhasN 0 correspondstothefrontsurface ofthelaserarray, whileplaneb Las Combiner field lens er lensletarray 1 plane,theemittershave not been subsampledandmixed 0 , a 1 Fi , anda 2 eld lens beamsareoverlap imagedover thefulllengthof 2 areconjugate toeachother, asareplanes a Uniformizer lensletarra 1 1 lens elements, with each lens element lenselements,witheachelement Mo b 1 dulator plane Fi Fi eld lens eld lens ys a 2 101 0
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 plane plane NA ( NA of 11.85mm.Inthearraydirection,830nmlightisemittedintoarelatively small 150 discussed previously. Again, the A020 arrayhas19multimodelaser emitters,each ence toaspecificlaserdiodearray, suchastheOptoPower OPC-A020laserthat was just afew percent. to nonuniformity residual the averaging. is goal reduce to the the general, better In length of the first field first oflength the lenswas chosen to theN overlap ( emitters between removing spaces the by effectively Lagrange direction array the reduces lenslet laser The array emitters. field full the each (2.47of the of light from array EFL) is collimate to designed mm output asaquicklydivergent Gaussiansingle-modebeam(NA ~ noisy, spatialprofile(see Figure3.6). Thelightemittedinthecross-arraydirectionis lenslet array. The corresponding N lenslet array. corresponding The the the of light at distribution radiance a more uniform create to lenslet pairs uniformizer a plane intermediate atthe illumination telecentric create to field adjacentused is lens the fieldlenslet and preuniformizer The arrays lenses. 102 illumination. Thus, the intermediate a intermediate the Thus, illumination. fieldthe in provideto lens telecentricity preuniformizer the does as manner same (the plane). modulator field plane modulator The the lens in of Figure functions 3.29 the first uniformizer array in a magnified and overlappingmagnified in a fashion thea onto array uniformizer first the field lens the of Figure lensletsimage3.29 to of postuniformizer together the with is parsed into N into is parsed direction NA of~0.14. tor arrayat1/6timestoprovide a2.7-mm-widelineofprintingspotswith anarray nate thefulllengthofmodulator array. The printlensdemagnifiedthemodula- 130 mmpostuniformizerfield lensprovided theappropriate magnificationtoillumi- ensure that the output faces of the lenslets at the The lensletelementsoftheuniformizer lensletarrayshad8.0mmfocallengthsto that the6mmoverall widthofthefirstuniformizerlensletarrayisfilledwithlight. such each 1mmwide. mm, The combinerfieldlenshadanominalfocallengthof99 formizer lenslet arrays, which were identical, each comprised six cylindrical lenslets, which would be acceptable for most candidate modulator technologies. The uni- overall device lengthof16.25mm. The designNA atthemodulatorplaneis0.023, this first-orderdesign example, comprises 256pixels, each63.5µmwide,foran convenience of conservation brightness. and power surfaces) basis set up of on effectively be the system, design will the the limit sag height on the of the overall array, of size on the the or limitations limitations size on (size lenslet width, limitations constraints Unless these manufacture. lenslet array uniformizer of the by constraints bound width the illuminated the with plane image The laserbeamshapingofthistypesystemcanbefurtherunderstoodwithrefer In a first-order design,the OPC-A020 using afirst-order In laser,refractivethe lenslet laser Thus, a second integration stage is used, which consists of the two uniformizer which consists stage two is of used, uniformizer integration the asecond Thus, The fly’s eye assembly further directed thelight toa modulatorarray, which, in a µ ~ 2 m wide,whicharespacedapartona650µ plane. The more N plane. The 0.13), withanon-Gaussianangularbeamprofileandrelatively flattopped, but a 1 , which is the magnified, and overlapped, averagedimagethe emitters, magnified, , which of is the 2 beams, where N beams, 2 lenslet pairs that are used in the fly’s the in used are that lenslet eye pairs integrator,the 2 2 is the number of lenslets in the first uniformizer uniformizer of number first lenslets is the the in lenslet work lenslet elements second the array in 1 illumination plane is subsampled plane by N the illumination ~ 0.187 vs. 0.77 otherwise). focal mm, The m pitch,foranoverall arraylength b Laser Beam Shaping Applications Shaping Beam Laser 1 plane were filled with light. The 1 beams at the a atthe beams 1 . The light profile at . The 0.63). 1 intermediate intermediate 2 plane plane - 2
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 illumination input, rather than a critical illumination type input. type illumination acritical than rather input, illumination providing as aKoehler regarded be can array. modulator difference tion the to The fly’sinput the into - providethen illumina to eye integrator lightuniformization for far-field whichnear-field the the designed in than lightlight profile,profile, rather is Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser sate for broadening of the beams at the b atthe beams of forsate the broadening compen to is slightly underfilled array second the lenslet so that arrays uniformizer efficiency. the layoutduring beapplied the can of factor For underfill an example, to helpbe modified also system design first-order can the addition, In performance. Lightas Tools) system verify and control to lens aberrations used be can or both, (such design software or illumination V) or Code (suchdesign software ZEMAX as necessary. if used be optics can printing phic but system anamor spherical, optics as shows illustrated printing residual. The the height. Smilecorrectionisusedtoeffectively reducethelasersmilefrom~ the pixel array, light fitswithin modulator waist the such atthe that beam Gaussian lenses provide to assembly laser a diode a set of the and cylindrical to mounted lobes. is ~ plane modulator atthe beam main the achievable.eye are results better System integrator, although light efficiencyin yielded above system on the based system design. aprototype with plane The modulator FIGURE 3.31 for edge broadening at either end of the modulator. A similar systemfor ateither end modulator. of edge the broadening Asimilar allowallowedto be the modulator plane overfill at Likewise, can factor an lets meet. where adjacent lens- seams atthe diffraction and experience light loss scatter from refractive with lenslets, to particularly opportunity, is an There diffraction. aperture During the system design process, detailed analysis and optimization using lens optimization analysis and system the detailed design process, During exemplary system optics of is included this lens that arod cross-array The atthe observed quality illumination direction 3.31Figure array the illustrates ~ ± 6 %
uniformity within the nominally uniform area created by fly’s the created area uniform nominally the within uniformity A measured irradiance profile of array direction modulator plane illumination. plane modulator direction array of profile irradiance A measured
Irradiance 0.0 0.2 0.4 0.6 0.8 1.0 1 plane induced by both lens aberration and and lens by aberration induced both plane Distance 69 % , with minimal light lost side the to minimal , with 69 11 can also be be also can 10 to~ 2 103 µ m - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 nation system (shown 3.33),illumi Figure of Incorporated in Creo critical-type amodified has design side. developed approach, other on the This roll-off the to by Gelbart Daniel waycompensatory a the thusadding other, to beam fromarray one profile sidethe of light the the emitter sloping of portion andredirect deflect that twowith mirrors This approach also reduces the system brightness because of the increased angular angular increased of the system because the brightness reduces approach also This only work also well will light profile when and ties, is symmetrical. the generally micrononuniformi but maythe have out direction, benefitin smoothing little array to reduce the effective the reduce to Lagrange. (not lenslet laser array 3.32) shown direction Figure in array an use also can printer systems, other of this many the window, in As athick as auniformizer. not as and atalow bar propagates and bar integrating NA, it such the that sees integrating the plane. modulator Conversely, the to imaged light underfills direction cross-array the direction exit array The face is then uniform. light is made direction array the that such direction, 3.32 shownas Figure in array provide to the in reflections numerous system the printer, is configured laser of case the the loss In brightness. of source anywithout occur significant can lightinputuniformization thenthe face, light fills input the If NA input the of beam. and the bar integrating of length the dent upon the is largely- depen of uniformization sides. degree on the The interface glass-to-air the (TIR) when reflects it encounters internally totally and length alongpropagates their opposing ends. output Light faces atthe input and the with structures rectangular solid generally dielectric are bars These length. light traversinghomogenize the their reflectionsto overlap projection by of in systems,and internal used aprocess operate a fly’slight or pipes, have which widely eyebars been integrator.also Integrating provided array direction light homogenization with an integrating bar integrating light homogenization an with direction provided array system developed printing Polychrome byexample, Kodak thermal alaser Graphics one As features. light homogenization, to approaches well important as other as systems have other with designed printing been thermal laser of other A variety a 3.7.4 104 bar. (From U.S.bar. (From 6,137,631. Patent 3.32 FIGURE As another example, an IR (850 nm) laser thermal printing system printing (850 example, IR another an As nm) thermal laser n A
69 rray Laser printer illumination of a modulator array, by means of an integrating integrating of an array, by means of a modulator illumination printer Laser that potentially corrects the macrononuniformities (roll-off) in the the in (roll-off) macrononuniformities the corrects potentially that Emitters La array P se rin Combiner r lens t - H ead Inte 21 Rod lens Rod )
ba wi gr atin r t h g
an I n t Arra c egra ylinder lenses y dire Laser Beam Shaping Applications Shaping Beam Laser t ing Mo ctio array dulator B n ar H omogenizer 10 9 , is provided 21 instead of instead - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 power. have also lenslet can more complex The ods. arrays designs, including aspherical (or- diffractive meth with optical binary) fabricated and designed be can described, previously several others and of printer, the of thermal laser type this in used arrays appropriately. lenslets of lenslet the shifted The axis optical but the with emitters laser achieved pitch lenslets be the same as by also the on the fabricating can results images overlap the modulator plane. magnified at Similar the such inward, that shift imagesto magnified the causes off-axis imaging system. of the This axis optical the 787.5 pitch (thescaleofFigure3.33obscuresthisdetail)onthelaserarray(776.3vs. emitter the pitch is than slightly lenslet the addition, laser of smaller tor plane. the In array - the modula at magnified and imaged are emitters element the so that length focal lens the than greater distance ataworking is located lenslet laser the with, array modulator array. (From U.S. array. (From 5,517,359. Patent modulator length. Figure 3.34 presents results of irradiance profile measurement at the lightthe at profile measurement 3.34 Figure of results length. presents irradiance low very has source coherence even main the if pattern interference an form will and coherent are mutually sources virtual These at entrance. reflectionits the source of a different one each presenting images, at itslight pipe exit forms multiple virtual systems The sources. multiple incoherent with mutually quasi-monochromatic and present even effects are interference in occur. These effects, can interference residual by caused which are features, nonuniform 3.34, frequency Figure in high-spatial field. the low-spatialto across respect with However, variations frequency as shown atleast illumination, uniform highly produce systems light valve can in illumination light. unmodulated and modulated the between distinguish to prism polarization device (a modulator), PLZT a with polarization-type system the is equipped and plane. shown, is a As modulator focus relays media lens the then the to beam the 3.33), printing Figure plane. modulator The lens focuses the light rod to in the the (not direction shown cross-array the In increase. such to an direction in the array modulator, system the to optical but is likely the tolerant illumination ofspread the 3.33 FIGURE Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser array and combiner field and lens array Figure 3.33)(see into a single element. Certainly, the use of light pipes (straight or tapered, made of glass bars or mirrors) or mirrors) of bars of use glass made light pipes the (straightCertainly, or tapered, system This µ 104 m, form, example), relative off-axis imagers, as used lenslets to the such are that
La 9 Laser printer using two mirrors to improve illumination uniformity to a to uniformity improve to illumination two mirrors using printer Laser also uses the potential simplification of combining the laser the lensletlaser simplification combining of potential the uses also ser arra lenslet array Rod lens Rod La collimating Cylindrical se field lens y r Intensity profiles Mirrors 9 ) Mo dulator arra Po pris larizing m Imag y ing lens Me dia 103 To begin 105 Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 C divergence by divided width)(length input beam upon θ the angle depends ratio light pipe aspect required minimum The light. laser of length coherence the the light pipe of reduce to the entrance plate atthe is placed tion, retardation amultiregion addi In light. the laser coherence the of length than greater and sufficientlydifferent exit the to light pipe of are the sources apparent rays of lengths the the from path the using is chosen ratio alight pipe whose so that aspect beam anoncoherentinto uniform 106 increasing the number of laser emitters can also help to reduce the apparent level apparent help the also reduce to can of of emitters number laser the increasing solution, 3.35Figure asimilar illustrates ≥1.5 For R(preferably ratio achosen aspect measure, acorrective cesses. As cause problems effects can for pro these other nonuniformities, spatial frequency exceptionally flatprofile. otherwise top clearly of be on the the seen can dips and spikes sharp The emitters. incoherent of mutually array an with pipe exit illuminated Burnaby, BC.) ULC, Canada of Kodak (Courtesy emitters. incoherent of mutually array an 3.34 FIGURE
with light pipes are also known. also light pipeswith are combination in using diffusers while of coherence arrays laser spatial the reduce to methods Alternate reduced. effects are or interference coherence scrambled, is then preferably wave. differences, about half retardation phase phase As small acquire will and mask phase of the portions different through pass will emitter same the rays and from thicknesses, different with provides mask phase areas The aperture. light pipe entrance the and bar diode laser collimated fast axis the between tioned L , the minimum width of the light pipe can be calculated from the Equation (3.1): Equation the from calculated be light pipe of can width the minimum , the In addition to providing redundancy and increasing available increasing output and power, addition providingto redundancy In insensitive too such are see to high- media print most thermal Although laser
Normalized irradiance 1.2 0.2 0.4 0.6 0.8 1.0 0 −0.6
A measured irradiance profile at the light pipe exit, when illuminated with with illuminated lightwhen pipe exit, the at profile irradiance A measured −0.45 W −0.3 min =+ 107 105 Normalize CR a coherent nonuniform beam can be transformed transformed be can beam acoherent nonuniform −0.15 LL ( R min =θ 106 d lightpi 12 co in which a random phase mask is posi mask phase which arandom in + 0 t RR ‒ 2 2x 2x
) pe Laser Beam Shaping Applications Shaping Beam Laser > 0.15 R widt min ) and laser coherence length length coherence laser ) and h C
. 0.45 0.3 : 0.6 (3.8) (3.9) - - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 ing optics much more difficult. Polarization multiplexing, opticsing much in Polarization more difficult. half-wave a which plate λ employed, (e.g., be can biners increase bandwidth laser but the wavelengths λ For path. example, optical wavelengthillumination multiplexing com dichroic with gains. the reducing thus brightness, emitter individual the reduces further 40 have typically 10 bars diode laser the-shelf effects byinterference averagingNotably, sources. more independent light from off- 7,209,624. Patent U.S. 3.35 FIGURE Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser 3 … as 810… as respectively) 850 imag and nm, downstream 825 the nm, nm, make can emitters for 50 + emitters Alternatively, multiple down combined light from acommon be devices laser can pha
Laser arrays Random se ma La
Microlenses ser ba arra La Dual laser array combining: perspective and cross-sectional views. (From cross-sectional and perspective combining: array laser Dual sk se ys r r 110 fill factor bars. Unfortunately, increasing the fill factor fill muchthe Unfortunately,factor bars. % fill increasing Emitters ) Ligh F olding mirror Ligh t pipe t pipe Microlense s F olding mirror ‒ s 19 for 30 emitters Lens Ligh Qu t pipe s adrant dete mirror Illuminate Sam Lens pling mirror Qu s ct Lens dete fill factor bars and factor bars % fill or adrant d surface Folding mirror ct or 1 , 107 λ 2 - - , Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 lasers in angle space. angle in lasers 3.27. of modulator Xerox Figure such the dependent modulators as TIR is not suitable lasers of for combining method polarization- use systems that this However, used. be laser, also other of can the axis optical light onto the that redirects combiner apolarization device of one laser and light from polarization the rotates 108 ing variation in thefar-field spatial lightprofilefromemitter toemitter, ifsuch a Figure 3.36doesnotactually provide themeansto correctasystematicrepeat- field lightprofiles,ratherthan the far-field lightprofiles. However, thesystem of presented previously, althoughthatsystemreimaged andhomogenizedthenear- Modulator array-typeprinters a 3.7.5 from two collimated laser bars laser two collimated from overlap lines. two illumination the by precisely used to a servo system is then detector adjust to two folding the mirrors the from detector.signal power of the The aquadrant to part asmall directs mirror modulator. of center 3.35, shown the coincide as Figure atthe Thus, in asampling multiple these lines that ensure to is required light modulator, spatial care the light to unchanged. is product essentially beam the direction, fast axis the in whereas, value product light pipe, is achieved of case straight beam in Aminimum two bars. of products the beam of sum the is the nearly net Lagrange the and is mixed, arrays two of each the light from direction light pipe. Array of atapered aperture entrance the grating light valve (GLV) modulator. such that a collimated cross-array far-field cross-array image acollimated such that cylinder lens, cross-array by a third before array modulator quently the intercepted slowly subse beam the are makes lensing then convergent. beams cross-array The narrow windows. as fast elements regarded axis The optical are direction array the overlapping fashion asilluminationtothemodulatorarray. drical combinercollimatorlens,whichprovides far-field imagesofeachemitterin of illumination. This slow axislightpropagates forward andencounters thecylin- profiles, suchthattheseimagesnearlytouch,therebyproviding ahighfill factorline emitter tocreatenonoverlapped magnifiedimagesofthemultimodenear-field laser collimating lensandanimagingforeachemitter. This systemmagnifies each provides an array direction (slow axis) cylindrical lenslet array pair, comprising a can be deflected into the common optical path. optical common the into deflected be can atleast device one laser light from emitted the and long along the axis, parallel in be placed can arrays is sufficientLagrange available. In there either case, laser so well be or corrected, controlled smile that require can latter but the directions, system, and the zero-order diffracted light is imaged to the media plane. An illumination by Agfa Corporation,theilluminationbeamisfocusedontomodulatorarray, Therefore, it is more common in these systems multipleTherefore, combine to light from these it in is more common As each laser diode bar independently provides an incident line of illumination of illumination independently provides incident line bar an diode laser each As This systemissomewhat similar tothefly’s eye-based illuminationsystem and beam the lens collimates rod (cross-emitter) the fast axis the direction, In 112 shown in Figure3.31,anddesigned in conjunction with this system, lt erna t e A 108 rray – 110 P Light can be combined in either the array or cross-array or cross-array array either the in combined be Light can rin 12, 110 t 111 - is directed by means of two folding mirrors to the the to of by two folding means mirrors is directed H have alsobeenexplicitly developed forusewith ead D 93, esigns 94 Inone exemplary system, 108 is presented to the modulator array. modulator the to is presented Laser Beam Shaping Applications Shaping Beam Laser , 109 As shown in Figure 3.35, shown As Figure in light 12 developed 11, 102 - -
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 lator array. modu the redundancy,of illuminate design provisions lacks source the uniformly to splitter) beam may provide of aminimum by apolarization means combines beams (which two-laser case the Although sources. laser either single-mode or multimode twomayby which one or be sources, laser flood-illuminated be AOM can array out consideration for redundancy. one instance, source In by but alaser - with is illuminated system which array other amodulator in concepts Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser can be high enough to cause significant thermal problems in the optics themselves.the opticsproblems in thermal enough cause significant to high be can welding, laser systems, and for densities energy pulsed used cutting and laser tems sys systems, laser energy ablation. such higher - IR as In plates by thermal printing systems have relative discussed printing laser of been processing enabling to These 3.8 optics, rection illumination inthearray andcross-arraydirectionstothemodulator. should occur(seeFigure3.7).Effectively, pattern thissystemprovides Koehler-like (From factor.6,433,934. fill improved U.S. Patent FIGURE 3.36 Lagrange growth. Alternately, a cross-array optical design was Alternately, optical proposed growth. across-array Lagrange to illuminate each modulator pixel modulator each identically. exemplary system, another illuminate to In provide does means the arrangement splitting beam the source, laser of the failure system is susceptible this the to While pixelmodulator beam. receives individual an of each such AOM-type that arrays, modulator a pair illuminate to splitters beam of laser, argon by an is split such apair from amultitude of as into beams beam, arrays, multiple light from extended laser the by diode combining further be potentially is effectively radiance source reduced. the is broadened, beam cross-array the However, correction. of smile ameans optics as cross-array the into as introduced deliberately are which aberrations in optics or mechanics, additional not require In general, the modulator-array-type systems will benefitcor systems the use modulator-array-type of will by smile the general, In The applicability of the modulator-type laser thermal printing system can printing thermal laser modulator-type of applicability the The
THERMAL EFFECTSTHERMAL IN OPTICS 5, 56, 108 in order to hit higher power levels at the media. In addition, there are power higher hit to order are in levels there addition, In media. atthe
Collimating andimag 61 Laser printer illumination with array direction imaging of the emitters for an for an emitters of the imaging direction array with illumination printer Laser – 64 Microlens arra so that the cross-array beams can be combined with minimal minimal with combined be can beams cross-array the so that La array se r Rod lens Rod ys ing Fa Combiner collimatorlens st ax 112 ) is nar ro wing lens Mo collimating lens 20 asingle high-power laser dulator arra Fa st ax is y 44 that does does that 113 109 an an - - Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 many of these materials, including crystalline materials such CaF as materials including crystalline materials, ofmany these thermal response of an optical material to radial gradients. radial to material optical of response an thermal (G), constant for which thermo-optic accounts the the and material, optical an to the other elements other havethe apositive d tible to thermal shock and fracturing, so care is required in their use. their in is required so care fracturing, shock and tible thermal to first requirement havingby requirement negative first d to applying a design approach addition effects. valuable be In these optics can design to reduce to occur, the it still Although use of autofocusor may significant. not be may resolve anyproblems that of focus depth design, and may or Rayleigh focus resulting shifts the thereof, range 3.8.1 birefringence stress (e.g., induced defocus thermally and thermal compaction or cracking),both levels energy the enoughAlthough not cause laser-induced to high are damage 110 the thermal glass constant ( constant glass thermal the of each which by upon depend two terms, sensitivities described be can effects. These cause different can gradients thermal and increases temperature soak d with occurs defocus generally systems, laser thermal In materials. weld other and and metals drill, to cut, used are field, processing lasers where have materials laser the emerged from defocus design for approaches optical laser-induced general, reducing In thermal ity assilver halideintermsofresolution anddensityforreflective andtransparent Laser thermalprintingmeets this requirementwhileitprovides thesameimagequal- that is environmentally conscious and dry, free from any wet chemical processing. Since thelate1980s,environmental concernshave demandednew printing 3.9 Notably, glassesandfluoride other fluoride calcium (e.g.,BaF levels 1 in those than range. temperature focus over awide lens maintain to so as the athermalize and solved achromatize to are equations simultaneous three and 20 kWmaterial, to a imaged be fiberto is laser hra printing. thermal thermal glass constant ( constant glass thermal elements amultielement in have lens that anegative d gradient suchglasses N-PK51A). as valuable be also Itselectto for can glasses one or more sensitivity gradient (e.g., silica)fused or near-zero thermal fluoride-variant calcium key. be tion can low-absorption with using glasses emphasize Such can efforts (e.g., (e.g., coefficient α absorption used of materials one or moreoptical ofmoderately close the peaks absorption to laser the defocus if wavelength thermal is cause significant only flux can evenoptical Although the laser printing systems typically operate at appreciably lower operate systems typically printing power laser the Although
OPPORTUNITIES AND CONCLUSIONS T herma 114 n /d can cause significant problems at these lightproblems these levels significant cause at can in laser used T l D , the change of refractive index with temperature, although thermal thermal although change of, the refractive index temperature, with efocus ‒ 20 kW laser thermal processing systems, processing Wof 80 amere CW kW20 thermal laser γ ), an IR laser system laser ), IR an γ ), which represents the thermal power is due change that ), thermal which the represents 0.001 mm ≈ 0.001 116 that reduces thermal defocus, careful glass selec glass - defocus, careful thermal reduces that n /d n T value, d so that /d T values. However, it that should noted be − 1 ) in the lens. Depending upon the system upon the lens. Depending the ) in 116 is described in which light from a which light from in is described Laser Beam Shaping Applications Shaping Beam Laser n /d 115 T values compensate. In one example, In using 2 and LiF and n /d T value, while 2 , are suscep , are 2 ) satisfy the the ) satisfy technology d n /d 116 T - :
Downloaded By: 10.3.98.104 At: 23:06 28 Sep 2021; For: 9781315371306, chapter3, 10.1201/9781315371306-4 Laser Beam Shaping in Array-Type Laser Printing Systems Printing in Array-Type Laser Shaping Beam Laser fiber lasers could be a useful high-power laser light source for these types high-powerof types light these be auseful could source for fiberlaser lasers lower and cost systems. performing design higher For example, pumped optically market place. of thesesystems,andthedesignsthatenabledthem,have beenproven viableinthe classical imagingandGaussianbeamopticsintounitarysystems.Furthermore,many micro-optics, andothercomponents,incomplex andelegant designsthatcombine laser beamshapingdesigns,whilegenerallyevolutionary, have employed thelasers, and new opticalmedia,have helpedtomake thesesystemspossible. The associated including micro-optics,high-power laserdiodearrays,spatiallightmodulator the spatiallightmodulatorarray-basedsystems. A rangeofenablingtechnologies, systems, optical fiber-based systems, the modulated subarray laser approach, and a rangeofviableoptical design architectures, including thedirectlasertomedia than silver halidecanbesatisfiedbyseveral multichannelprint-headarchitectures. images as well as printing plates. Laser thermal’s requirement for more laser energy REFERENCES printing. thermal laser port and solutionsdesignthe benefit approaches potentially developed which can to sup color projection image laser such as printing, beyond thermal laser Moreover, opportunities market are there
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