On Hologaphy and a Way to Make Holograms
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ON HOLOG}iAPHY AND A WAY TO I'{AKE HOLOGRAMS by J. Pethiek
Cover drawing by Peg Bennett, based on a seulpture by J. Pethi.ck &n #ltrvly rt"{ A BELLTOT/,JER B00K t. A *}ry *o 4o*" flohg;*r:
' 0 Belltower Enterpri-ses, 1971 Sherm 1z
ON a Tube-mounted optlcar components inserted into washed HOLOGRAPHY silica sand provide a highfy stable a"A ff"xiUie AND system for rnaking holograms, The plywood. box eontaining the sand is rfloatedr on an inflated WAY TO MAKE HOLOGiiAIVIS inner tube for further vibration eontrol. by J. Pethick
A Belltower Book
Courtlry EdifiE t @ published in cooperation with the Umbra Foundation t\ BELLTOW.UR ENTJIRPRIS.!,S 2358 Lakeshore Rd. E. Burlington, Ontario, Canada
I ,l tu-.-* CONCI;RNING HOI,OGRAPHY
Holography is j_n Denis Gabor, nho eoneeived the idea of holography, its infancy. This means that nev nade information i_s continually tecoming first holograms wi-th a complicated whi-te light available, and source at the Imperial London, England, huge junps in overcoming its technical limit"iio.r, Institute in are being nade in short periocis in 1948. Because of the impractj-cability of the light of ti_me. source, little more xras done untj-I after the j-nvention There is littl-e in th-is booklet on pulsed of the laser in l-950. The laser was to supply the holography, ideal light source holography. whieh seems to be a much ress restrr,ilil-ray tI rork. for continued research in But at present it involves a great deal of Lxpense. The sand-based system describ-d her., originaiiy Finmett Leith and Juris Upatnieks, working at the developed and implemented at Editiori University of Michi-gan, obtained remarkable results tr,"] in Ann using a laser to nake holograms 1964. Their results Arbor, has been proven to be an i-nexpensive in and efficient-lrlichigan, approach to holography. ' established holography as a medi-um of the future, enabling the storage or rcapturing, of three-dj-men- sional visual information two-dimensj-onal plane. I would J.ike to thank and. acknowledge the help of on a Lloyd Cross, Allyn Lite, Don Broadbent and nany others In a short time other laboratories were nraking holo- who contributed towards the infornration and exieri-ence grams, but holography did not seem to serve the highly that have niade this bookr-et possibre. speciar thanks Lo l,largaret technological industries rvith enough economically Southcomb and DaryI Sharp tor typing and editing the material_. feasible applications. Consequently, it was often treated merely as a laboratory whimsi-cality. The ' search for applicati-ons conLinued, while a few people, The way to t,echnical and artistie acivance holography in including some of the scientists working 1n the l-ies in the sharing of resources and information. rt fleld, is hoped that the non-profj_t Udra Foundation, were learni-ng more about the potential and ]imitations San of holography simply as a visual meciium. Francisco, wirr be able to assist many of those inter- ested i-n the holographic process and. other technical media. r. f One of the reasons for such a SlglL-AFg,kgiI& is that {f j the three-dimensj-onal quality of ho}ograms cannot as I yet be reprod.uced by any of the mass media. An arLj-cle and photographs published in LIFE magazine, for instance, J. PifTiiICX took great care to shovr varj-ous views of a holographic j-mage to demonstrate the three-dimensionality, but failed to make clear the fact that until you see an actual hologram, no rranner of clocumentation can illu- strate i-ts unique spatial quality. { The nunber of holograms avai-labre for peopre to view between 1964 and 1968 was very 1imitea; nofography waS When the film is developed looks a smarl and inaccessibre area it no more like a of research. t*o*"rl", picture than a gramophone record 1ooks like mrsic. But the opportunities to view holograms are now more num_ erous. The when the film is illuminated by a monochroratic light Imperial CoIIege in London has an Open Day soufce, the i-nterference pattern in May each year when the public causes the original are adrnitted, ancl in photographed object to become visible in three the ELectrical -bingineeri-ng department ther" *." usuarry horograms dimensions. .When you move your head., you can see on view. conductron corporati-on of Ann Arbor, raroundr the obJect. Michigan, has several first-rate htlograms on oisplay in their ! lobby. An exhibiti-on of horJgrams uy nait:-tns, i The one rnc., Ann fact that can record on the holographic film Arbor, toured in the autumn or l9z0-to museums I I or glass plate only what in Rochester, Syracuse 'l is illuminated with laser and Albany, after opening I at the is a fi*ilgligLintrinsic to the medium . Filch College lvluseum york, ll Lllett itself of Art, New and a similar It is a form - I of spoilight exhlbition was on view at the Exploratorium (parace illumination, with the sur- of .t rounding darkness being a black voj-d. The size of the Fine Arts) in San Francisco during the summer of I9Zl. I science I Iaser and the amount of eoherent 1ight iL gives off museums and many erectrical engineering, opticar determine the size of the illuminated area, and laser exhibitlons have examples but even of holograis. the smallest hologram will demonstrate the mediunrs unique qualiLy of three-dimensj_onal space. Some of the companies currently working in holography are: Edi-tj-ons Inco; rrow located in San Francisco; Con_ Flost holograms to date have ctuctron Corporation, Ann been of the transmlssion Arbor; T.R.W., Reciondo lieach, type. To be viewed, they need be california; Hughes Research centre, to illuminated with rviaiibu, californii; either laser light or light from a r+hite tight source and BelI Laboratories in Murray HiiI, New jersey. In ilngrand there physics which has been flltered to one particular wavelength are the Nationar Iaboratory and or color, and preferably frorn a point (a the Imperial CoJ-Iege. source srnaft opening or filament that allows most of the illumina- tion to come from one single point) so that it acquires Most holograms are monochronratic and vier*ed as though a laser-Iike quali-ty. For anyLhing larger than a {rl one were looking through a wj-ndor"r - the glass photo_ by hologram, a problem graphie plate being 5" real occurs after the holo- the window. They are made with a gram has been made. the image, a 1ight raser emitting a continuous beam of light (continuous Ig_119glggrt-e_ wave *-s,gqr-c_e*1llst- shine on the plate at the iame angle af-tia laser), using an inanimate object as Lhe subject. ieference beam For the purposes -th^9*Since- g_liginal *tien Uhe pfate wal exposed. of holographS one can think of the sriialf, inexpensive lasers are inaoequate, there laser as simpry a special light bulb, one whi-ch enri-ts a single remains the need for efficient and cheap light sources color of coherent light (figilt waves of the to illur.inate transm_issi-on holograms. sanre wavelength moving in the same dj-rection). Several general light sources To make a holopram, are currently being used an une4posed phoLographi_c film is lo replace the more expensive Laser sources for viewing. 8fitr-ffrirdYtr"*;bjecr. ii,.ri of a laser beam i1lum- For inates sharpness anci clarity, the fi_Iters have to be of the obj.ecL, and the |estrof fhe beam is deflected good quali-ty, and the brighter to the fi-]m. The the source, the more film receiveslthe wave pattern of possible it is to view holograms in a normal environ- both the cii-rect laser beam and Lh" lauu. iiglrt reflected ment, from rinterfeience thrls reduci_ng the need for stringently light- the object. The result is an paLLernr cor:,trolled areas. The white recorded on the film. light sources novi used include tensor high-intensity bulbs, microscope illum- inating lamps, quartz lodide bul_bs and the more expen- sive arc lamps. The brightness and intensity of these T \ the brain of images of human subjects that appear sources are very important because they enable a good relate precisely to the original extremely real- three-ciirnensj-onally and yeL are unreal, quality hologram to i.e. monochromatic, in color content. The eye and the subjeel netter. To have good holograms not adequately whole potenti-al of the medi-um. brain have the ability to intuitively know some of the vieirable nu1lifies the colors of a composi-tion by their Lonal rel-ationships, and the people on some occasions hologram that has a great many advantages flesh coloring of The type of seems to be rpaintedt by the eye. i" tnl'reflection hologram, ?: it needs no special point light source illuminates it viewingGurcel-A Pulsed lasers expensive and generally and' brightness' In fact, an are available only with glod definition j-n scientific laboralori-es. Consequently few holograms ordiniry light bulb ad'equately recreates the image, and portraiture is not nec"ssary to view reflection of animate objects and human have been made. because of [nis it Pulsed lasers for holograms with enough lllrrminated holograms in specially darkened areas' However, at the holograms are somewhat diffi- space to allow three-oimensj-onal portrai-ts of such sub- presEnt time reflectitn jects as an all-star football Leam, astronauts, or a cu1.t to nake. They present problems in resolution and the degree of depth and pornographic group now exist in the United StaLes only color smearing whitfr restrict aL three or four of the larger corporations. However, view obtainable in the hologram' angle of a ny ma rk e d e i t he r i g__...ggl +Il_pj::rs*trp-rlt=o " Iplgg,ryp}i - I an ordinary filtered sions_or the availability of pulsed lasers, will bring [*',ur, . hologram is viewed with Tli6Tacility economicaliy the reach smaller spectrum appears, spatia]]y Uinin of ilr-ri[. Iight source, a color compani-es and studios, leading to more widespread fo the subject matter, but without definition. , r""iat.a in activity and realizatj-on of lhe full potenlial of \r\ iThe colors are Urigiit and clear and seem to float holography. \ ispace. This interesting phenomenon can be used to Y j IIIumi-n- n,' three-dimensionai color composi-tions. ilt ttre present Line, continuous beam lasers can only ar/a" "i""t" an unfiltered white light I ation of a hologram with !smearr jmake holograms of :!g*igC-!S*CUbjgq!-s. There are many , causes tf,e holographic sribject to across point-of light small, relatlvely cheap lasers of this type, including i ;h;"o"""u ,ri"iur" spectrum oi color. Thus, a kits that are aseembled by the purchaser, but most of becomesalineoflightthatcoversthevisiblespectrum these moment, plane are, at the inadequate for holography. and., sinr-ilarly, a Iine becomes a plane and a They ean be used, but Lheir power is so 1ow that expos- becolnes a sol-id. ure times must be very long. Thi-s means that a long period }aser of stability without vibrations is necessary. To make holograms of living matter or people, a Larger lasers or improveci holographic emulq-tgpg could of coherent 'sizE is requireO Inat emits very short bursts fEA" to-A"reducti6il-iitfi-e oi 1"r""" to make Iight.- This is called a pllsea laser. (The process is hologramsr-gt"a" potential"-,iffia of photograph;r') incfdise"in tG size si-milar to using a flash EoIE-It' high speed holograms using the same lasers. The burst of laser light occurs so rapiCly that in effecL tL freezes a1l movemeni, and therefore greatly increases Conceivably, emulsions will improve so much, both in holography' !' the pot"ntial subjecl nratter for .*::.".C-l3e.pro
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There does exist hol-ographic film, with an obvious Many people have been interested enough in the holo_ application in three-di-mensional movles. lu[any of Lhe graphic process to make cursory investigaLions into its major companies with holographic facilj-ties are worklng potential and availabirity. But pessimism o" unreal or have worked on some of the problems i-nvolved, and prohibitive eeonomics have indirectly subdued the very some of the theoretical work has already been published. ones, artists and sclentists, who mi_ght be able to make The problems are basj-c and diffi-cultr.l,;a laser capable the medium somethi-ng more than an inieresting toy. The of many pulses per second is needed to do the shooting realizatlon of holographyts potential is dirEctly re_ so that the motion is sufficiently convincing to avoid lated to the nunber rfllcker-flashbackr and variety of people frorking in i-t, the effect of early movies;.gThe and to the amount of money avai-labre to sorve i-ts real problem of viewing, however, r+1ll require a great deal problems. Those interested i-n the med.ium, either as a of research before any really satisfactory results are purely aesthetic statement or for its numerous corutrer- achieved. This is assumlng that we conceive of and eial applJ-eations, need not worry unduly about the rel-ate to moving lhree-dimensional holographic images economic and technlcat problems, as the r:najority of on the same terms as we respond to photographic foo+.age, these are temporary and solvab1e. 'l in which case viewi-ng a holographic film would be like . viewing a television box in which the television screen Holography is simple. Anyone r*ith interest, basic in_ is actually holographic film moving across that area. formation and minimum equipment can nake a holoAram. Maeterlinek said of rnanrs use of toors (trre terEscope, e I gv-iq o n i s a I s o a c e rta inty at .Ih,Ig,g:*d:n-"n9.1_q +e-_1*. _t, 1 for exampte) ttrat the discovery of a new star or phen- bud wh-ethbi purely holographic ione-time, ii"Tilt be a omenon i-s not nameci after the too1, but after the rnan process is stil-l open to conjecture. Three-dimensional who discovered i-t. Technologr has a host of new tool-s animated films can be rrade by splicing together 5" or for those r*ho are interested, but it will take time and l0'r wide holographic film and viewing it di-rectly as tarented people to realize their intrinsi-c varue. The one views large transparencies. Any research i-nto potential of the future iu !gg, given imagi-nation and either three-dimensional movies or three-dimensional the will to encounter t,he unkrrown. televisi-on i-s generally lhought to need very heavy finaneial backing, but much could still be done at a rudimentary level. iiiore practical experimenting is needed to give concreLe information on what the real problerns are and how to deal with them. *{ +jolography involves many unkno'wnsr Il is still a medium 1l-.."=\Lhat has not been carefully thought about by many people. ' .":- Too much of the ihinking to date has related holography r\'')'' *)- Lo what we already know about other nedia. In thinking about holography, we neeci to start afresh ancl derive our answers onl-y from the evidence gaineci from holography itself, leavi-ng old concepts to their respecLive fields. The applicalion of holography to communicati-ons and the human environnent could soon have a very great and far- reaching effect on our society. Uslng holography, the physical environment coulci be anything that man can conceive. liolography can creaLe the future.
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I -L-I ;- F. \ iR\ $$ PROCESS. iiQUiPlrvriLitiT lJrln f'uCif,rttUS
Explanation anci start.
K Holography is a process r+hi-ch uses Lhe special prop_ erLi-es of laser light to recorci three-dimensional b infornration on a two-dimensional plane - lhe infor_ mation being storeci on right-sensitive emulsion in the form of an interference pattern. The visual infcr- mation ma;r be retrieved. wi_th a laser. or monochromati-c Iight wh:-ch re-illuminates the emulsion, passing through the interference pattern. Holograms have to be taken in conrplete darkness, so that ihe emulsion is \s' exposeci only when the shutter mechanism is opened. lo N allow the laser beam access lo the phot,ographic sN plate. " * rr continuous wave holography (using a laser that con- :addbinuously enriLs lightt ;h"-ir"orog..phic working space (n anci the laser and at,I the opLical components have to s- be Various means of isolating the \s "y"]!_f_+.!_"l"o.I]^:-{tgp_* set-up from iLs surroundings maJ/ be used. One of the q--. best and simplesl is the sand. box system, using fine sand to create mass and then isolati-ng lhe box from the S. ground b;.r pJ-acing iL on inner tubes. N sJ t. A garage or basement concrete fl-oor best (wooden \i \tIr i"s is I t-llF floors suspencieci above grounci level will amplify even the slightest vibration, Nr* I regarciress of horv solid Lhey \ t1\ I seem) , but an;,r place awal' 1fo* people and Lraf f ic, such I as in the country, an -.1 \ is ideal location for holographic $- N. wcrk. Once the sanci box anc in*er tubes have been sel up, Lhe optical components are mounteci on tubes and sluck in the sanci. _Th.fiig allows for fle,xiLiiit;r and -quick aojuslments, with immeCiaLe staL,ility ,"" _the tubes are reJ-easeci, since ihe Uott'om-po:.tion"oo.,'n" of lhe tubes become fi11ei wilh sand, !.Jius lowering Lheir \ ge_ntre of gravit4. LS No' The fol-lowing pages oeseribe and i-liustrate the various ** Ni cornporients anci hor* to use them. F>Fts \ stN l,;l
i:r- F^v .:-€ N -:-- ::-eei, *' x Bt, of one_inch p1y*ood i_nto one * -i c-- r -,_ | --=-: - r- a, Lwo pj_eces lt x i1 I and Lwo pieCes \ :: l ':0" . r{ \ T -' \-{' \ \ 2. lo-ior:r a seuare box, put the four pieces togeLher tt ':si-ng 2n x 2n blocks at the corners, N are so that the si_des $, I2'r high; then mount the box on the 4rx 4rbase. \ \ t Cover J. the outside of the base r+ith thin sponge or t' carpet rnaLerial. !-* ) Place the box evenly \ and squarely on top of one large tractor tire inner tube, o" for. smaller inner tubes.
q Idail a piece of r*ood along the boxrs edge, to hold t the laser.
6. !'ill the box with sand to about two inches from the $i top. (The more sanC, the better tr, + vibratj-on.) insulation againsL \Sr ,r Washed sand seems best for keeping I dor+n the dust, buL any"iti"" fine sand will do.
a The tubes for holding the lenses and mirrors can be crdinary plumbing waste pipe (black plasti" o. Lwo, alrr*inur) three or four inches in dianeter. They can be cuL about 14,, to l8rt \ longr.depending on the components they hold. larger tubes firred with sann can be t extensions.- used as \ The mi_rrors anC lenses can be glued to corks i. that fit into the tops of Lhe tubes. The tubes are then n simply stuck firmly into sand. r.rt the .t t The Iaser. I i _:.11e o1e bean anC dividing it lnto two, wi.th both ra;rs -cgrdng from Lhe same cavity tuUe, ensures that )( \ be j-n the light' (a {. _l{iU phase. A 1aser is used. because the Iight it' qqhe"renl o :.t=,is i111.the 1ight travelling in lhe same ! GLr"ecL:-on and parbllel) and r49lrggh-f_amatic (one color of lhe spectrum - .9lr3=,-llgvglengtffi
u !:, -\ \ (\ \ A laser takes some Lir,e lo beconre stable ano shoul. be \. b lr turned \ \ t N on for a fevr mir:utes pri-or to use. Iiot, all 3 t S lasers are coherent enough for holcgrapiric work, buL q \ \ some that I s 3 are i,ncluie the fotlowing: ) \ l I Helium neon - red (most comllon gas laser) . One-half to I I ft\ :. { \ IOO milliwatts. Llontinuous wave. \ Ir\. I G h riD N \ \ t \ Argon - green, gas laser. Pulsec or contiriucus w.tve. .\ I \ \ N Heliurn cacimium - bluer gas }aser. Continuous wave. N t.o. Ruby - red, pi-ece of ruby rod (c;'lincrical wit.h paral}eJ- t l ends). Pulsed. I $ Krlrpton - white light, g&s laser, water cooled. ConLin- I uous waveo is t' A I0 mil-Iiwatt laser i-s adequate for l+,, x 5u plates. t A 25 miiljwatt laser is aoequate for Br x IO,r plates. \ Larger holographic film gives greater l. flexibillt;1 in I the choice of sub;ect and the amount of ill_unjnat.ed T space around it, but more iight is neeciecl , whi-ch means ti \ larger lasers must be used. \ N A prism can be sel up in the path of the light, breaking \ it into the four primary colors, \ red, -trellon, blue and iLs green. lviLh a prisr,atlc assernbly, antr of lhe I'our color"s can be selected by tuning the }aser. This gives ar very beautiful and versalile lighl source, ,: Dye lasers, which use liquid d;rs5, glve large color. ranges whicir are alsc tunat--le, }_.ut, not, sufficient.l;r coherent for hol-ographyl hor,rever, the:;, would bt: cr pos- $ si-ble cheap iilunjnati-ng source. ii[re !'or conlinucus wave hclofraf,;h.-,:, pr-ovirjing lhe,re is no vj-bration pr<',blem, 1t ls possible lo m.rL;e larger plat,e exposures usi.ng small laser"s ani ex,co:i-n5; tlrr:in for iorrge: periods. in Lhe counlrJ/, if,r{a.-r/ f:.cm lr.affic and people, a small one miLliwatt l-oser night br: ,.rse Thq,sbutter. Since exposure Limes varJr a greal deal, some kind of shutter rLr:.st be useci. The laser iLself must not be o,*tt* turned on and off as this woulci cause vibrati-on and affect lhe stability of the light. hhatever is usecl as the shutter should be suspended without touching Lhe sanci box, the laser or any of ihe componenls. +-----l tr*,t/a o4 A mechanical oevlce, such as a solenoid or relay swiLch, 4^ a*,*illt, could move a light piece of mat,erial acting as a shutter Lo intercupt lhe beam. tsut it would also be quite ace- quate to si:r-Lply hold, by hand, something whieh is light- absorbent in front cf the beam unlil you want to expose the p1ate. _Ibg s-!!rt!eq mecfranism must be placed sone- where between the lasei and where the beam is split.' The laser beam may be directed to the optical components in the sanci box by a transfer mirror, which can be any f.ont sufface _Ui.ryo,I. Back surfaced rnirrors are not suitable, as lhey break the beam up into many small bearns ,.ilrr*-f pr*rlo . qrr..( rxL-- and a great loss of light occurs. The beam splitter. ile p.// 6/, 42 *7La.-ct /eo.*, t* ,*;^/ 4, ir.*, s7tr4a * 4< /4t. This is an opti-cal pi-ece of glass which is partially f*, si-Ivered and will divide the beam ,lr;* /eo*t b ,*L.rr,A./ laser into twol but an -r/. ordinary pi-ece of glass wi}l work just as r+e11. When ?li?rt ,L *o",n a4b4 *]12 eb|"t the beam hits the glass, a srall part of it is reflected (t *V a* '*4?e c*rti 7,i-t off t,he front surface anci the remainder goes lhrough i-t. o*t *4 a,/l,x- The part reflected can be ciirecteci by changing the anqle "//irf) of lhe glass to the beam. -llqr- ?+ *4 ?Za.t<.- -Since-j.!.=19..I..e.t__1g-qlgg. off Lhe ,front surface of the beam-splitting glass, it is weaker and shoulo be used as the Je{ereg%L**j this }eaves -&alre.. lieht to ilJ-11{itnqtq. llre gbjgct. Eouidistance of beams. \i fhe object beam and the reference beam shoulci traver the o/yrt* - d.i.stance from the beam splitter photographic Si"*"r to the '{...p}ate. The di-stance can be a}tered by usi-ng one or more ln front surface rnirrors. Each raser has a knowrr coherence length whi-ch enabres an estimation lo be macie on al-low- abl e divergence in path rengths before-'lhe hologran will moBbe successful t /e.^ . The beams, after being spread wit,h ,//, lenses , are con j-cal . L5 .q 1ry. Thj-s must be rnade in total darkness, the only light bei-ng that coming from the laser. The two beams are generally referred to as the object beam (the beam that illundn- -e-6 ates the object or EiEEEiFthe reference beam (the F lr\ N- beam Lhat is dlrected to the r:-ghtffiIsion on q the photographi-c fi-Im or plate). reference beam is t- $. 3!e - P usually much stronger than the obj-ecL beam beiense- t' )\ ;redi,-[a.:-or righf i] Iost illuririnating the object; ffi 'Eedin "i 6"'IdEt -"e s"Ttr'6firyffi through a lens that expands it to cover the enLire plate u as evenly as possible. A pin-hole is used to keep the N reference beam evenly intense and free from dust and $ marks on the opties which would otherwise show on the j-s s{ plate. (This not essential, but heIpful.) o \ The object beam, after being scattered off the object, t!n and the reference beam both hit the plate and make an interference pattern whi-ch is recorded on the emulslon. The ratio of intensity al the plate of one beam to the ffira} rule, the reference beam is L or 2, ancl ihe object beam is I. This ratio, 1:I or' 2:1, serves most situati-ons and can be judged by eye or' meter, If lhe reference beam is too strong, it can be red.uced to the required amount by using a holographi-c plate r*ith varied exposure across it. A spatial filter, although expensi-ve, is helpful; used as a beam splilter, its gradiated mirrored surface allows exact beam ralio adjustment by selecting the plaee on i-is surface that allows the right light transrn-ission. For transrnission holograms, the emulsion side of the plate or film is placed facing Lhe reference beam and !\ G Lhe object beam. l{iih this kind of hol-ogram, i-t is much s harder to brightly illuminale transparent or very light- f. absorbing dark objects. The exposure ti-me increases as the area to be illrlninated i-ncreases. $ It is important that no light fron the object beam should *# hiL Lhe plale directly, and no light from the reference 't'beam shoulci hit the object. L7 Developing. Bleaching. Holographic plates are developed in the same way as }lt."l developing and fi:cing, some plates are bleached ordinary black and white photographi-c film. The plate (taklng out the silver nit,rate) so that the plate loses should be taken, still in total darkness to ensure all its blaekness and becomes armost rransparenr. There are numerous agai-nst further exposure, g1o $ve_!9pgd,_-{9.I {i"S,.._T*.f' bleaching processes to lmprovl tf," light g"Ug"E i-n ordinary photographic developer (or more speb- transmlssion of the plate or film. This tends to ialized developers are available). It should. then be brighten the hologram. placed in a stop fo-1 sqgglq: and fixed for _!at!j-n !,hirty about ;[tUq ggl_4gtes standard fix (bg}.-fglreg_!:.gg A simple and efficient process for bleaching in one step o"rii be ttre- prat6j;tldriiil" (as opposed to more complicated Jglqef*u-ut "6t fixed). p.o"""u""I--i"1" fol_lows: b"e-rinied'Uetw'een bach sf,agb and finat--ln [ashe4 for a [email protected] cyanioe and B qmn cuprj_c r-o$"id few minutes, rinsed in photoflo, and then allowed J e- !s *Ltt mi_r-ri r iL re s o i r" G..E*ffiT ffiffi . to ory. Iike a developi_ng tray. Stir un{ii all- the powder is dissorved. rt shourd be agi.taled gentry whiie Lhe plate An indication of the brightness and sharpness of the is complelely submerged in it, until thl black i_n the hologram can be obtained by sinply holding it up to an emulsion di-sappears. Bleaching an over_exposed plate ordlnary tight bulb and assessing the brightness of the might resuli in grai_niness or iuzziness of the image. speetral srre&rr The side with the emulsion is deter- When the black disappears, the plale must be removed mined by wetLing flngers or lips and feeling both sides inrnediatel;r and washed carefull;1 for" ten or fifteen of the plate at a eorner for a few seconds - the emul- minutes, to make sure the bleaching action is stopped. sion side is sticki-er. Photoflo can be used to even the dr;ring process, or the ivianufacturers of plates. ]rafe can be squeegied ar*a*"a--er i€ir-t*ffi, .uoo, temperature- The wer emursion swe[s so thai Lhe crarity (Holographic emulsions have an A.S.A. of less than 1.) of the i-mage cannot be assessed until the emulsion is dry and in lhe same state as when i-l was laken. Agfa:Gevaert Plate sizes | 3 L/l+tt x t+ L/Zn l+'1 x 5't - , , CoaLinss. Bll x loil, ]l,r x 1{'! , IB,r x 2l+,,. + - Plate numbers: 88J0, 8875, 101170, LAE75 The emulsion containing (4 the interference pattern (Lhe times faster than 8870 and 8E?5). vi-sual i"nformation seen as a horogram) is very sensitive. It can be.protected against r+ear ind handlingl elc., by - Processing: Agfa fine developer. Stop. covering (i.e' uacking) the emulsi-on side or"ine prate (Other speeds Fix. emulsion are with a piece of glass or clear plastic, the eOtes taped available, also film in 35mm rolls, or put in a frame to keep it clean anci free from dust. and 10rr wide.) There 5$ are also some liquid coatings that can be spra;red. or brushed on quite safely; two such coalings, which are Agfa-Gevaert will take speeial orders for 3rr x 4rr verlr tough, are Polyurea varnish, and tiquil acrylic plates and wj-de rolls of film. thinner 42r' with XSrlene. These are pul on thinly so that no ' chipping or cracki_ng occurs, and may even be used on Pl-ate Kodak - sizes | 3 L/t+,, x t* Lfzn, 4,, x 5r,, Bn x 10,. fi^I*.^.Jyf"?"g_h-a's aovantage of having the same rerractl-on lhe inrjex - Plate numbers z 6{9E. JJr as grass ano can Lherefore be used betirreen*, glass anci lhe emursi-oi. This seems lo increase the - Processing: Dlp developer. Stop. Fix. brightness of Nhe hologram, but a good seal around the eciges is necessary or it. will evaporaNe. 1B L9 VlewinA. (t *r,rr-r, ;nara /'loVo'" ,.r2./. (./rr*r,,1,y 7"4 The hologram is now ready be viewed 'lltt h{tAt- 2l Less bright, but a simpler and cheaper source, is a S o tensor high intensi-ty lamp with lens and filter. How- f\ ; sq ever, because of the less efficient filtering, lhe light x' Fr', * is not as monochromatic as with a l-aser source and con- r$ $x lr sequently the sharpness anci clarity suffer. \ F xt= i If clear images are not of prime importance, then \<. ht \ illum- F,F s i.nating with any bright light will give an elemental \ I reconstrucLion of the image, with Lhe spectral smearing N.$ o R I of a1l the wavelengths of light. These smears are stirl spati-ally recreated, but without any [I t N distinct object or t.t \ .L=. l image being apparent. The sun is an ideal source for. t4 I t\ such elemental reconsLruction. I or N:11 a x 'i \ \ G { \ a\ * T \s F t _Thg bgs.ic advant?ge of reflection holograms is that there ;is..--fg light source prouffisource wiII- .N f$ recreate the image clearly, because in Lhe making of the N 1 \ t\NS ,j hotogram the emulsion itself acts as a light filter. \ ft ' Reflection hok:grams, unlike transmission holograms, are R d illuminated from the same side as the viewer, but lhey cC F. NI : N stilr require an exact reference angle reconstrucli-on. l. .N x They are generally G angle sensj-ti-ve, wilh a narrower angle t5- of viewing, but they have an interesting color less 8- t+ trarifiedr - s,N than laser illurninated holograms. N _Irciq_glg*_+ggge*helgggg!, can be made exactty like transrnission holograms. Insleaci of using a f'Lat mirror \ \ . to reflect the reference beam. a columnatins mirror is , .t x' used to keep the right from expandffiure sta.. .I. $t. N and development, the image is reconstructed between the \ N l. observer and plaLe (or \ \ the in Lhe observerts own space). c{\ N s t The size of the inrage and lhe sj-ze of the plate (back- $--+ tt ground) determine Lhe angle of view, as thl t\ lryegq.Jg$* tl \ g*_-q{L!9gg1{ edsg of the ptarg.. N _the- lp N \ ls N II been rnaoe. They are more com- : ! -Igll-g919llpl9.grel4".,haveplicaLeci because each plate IF \ s contai-ns lhree or four sep- $ ,$ arale holograms, each one made separately wiLh a oiffer- I \ t'.(' t$ enl primary color of laser 1ieht. color resislration is $ also a pr.oblem, anc adeitional equiffit .tr.ffiffi'I7" NN i\ N $'r lasers are neede Libraries are a good. source of infornption. Optical and mathenaticar expranations of the holographic pro- cess can be found_in almost any book on frJfographt. A greater depth of information can be obtainEo trom many published articles in l,ASr,Ir I'OCUS, OPTICS TODAY, and scrbMrrFrc AlttRlcAN. some articles have arso been 'l/urrrAL printed in photographic magazi-nes. l,ruch of the mation infor- 4 in these articles :-i airficult for the rayrnan to-understand, but the diagrams are usually very good and informative. J-/z zo.1 ,a *Q lzu 4e /,-a ^4".f,.rt Front surface rnirrors can be obtained fror^r surplus stores t/e ,r*,rfZte u;4a/< , /4/ *.1 *d/ ft+,*t"4b a- or rni*or grass eompanies. Opticar fillers and beam split,ters can be bought through UDIIiUNDrS SCIjiN_ $/rLi "",f&. T-LFIC. Spatial filters a.ra pirr-frole assemblies wilf probably have to be ,A ,,o /*",4*,, #z auo, sAZZ obtained fron one of the companies J/ //"t ^Lge actively involved with holography or lasers. Jz *tot.-fr/ za*"" .-./ ,-Z;/- ,lr"/;*"Xz Comrnunications to the author LrateMO -Z"U relatj_ng to material_ 1.. _l Ua,tcl i-n this book nay be addressed to the pubh_sher. St .,lo S'oP ' . l rr 'c) .. v*,'rrl@ u,xaq€ prr'y'f"l J/Z7,t"rr/tt"oVi. t,aajl€ r,o +/e- raglery p"*stu't/ /or( fr /"*f hu.z,..ro*f 7,ila 21.4^"2 { V"'+*&r n^oq1/ /lrZr*y/ *."f ,+"^J9 -r4,/4, /lzdz i'aytes zx ut tA "*r4./ fr4r'' "*'4 ' 25 *ri { Notes Biographical Note Jerry Pethlck tg a sculptor working in pleatlcs, holograptry and other three-dineneional iJ-luaionary proeesssa. He lE an AEsociate of the Royal CoS.lege of Art, London, whoge work haa been exhtbtted ln F flve group shows ln England, tnoludlng one at the Whitechapel Gallery ln London. He has been awarded two grants by the Oanada Council. Hta'hologramo, including the worldrs firet anirn+ted holographic f1Lm, have been shonn at the Finch College Museum of A,rt (New tork), Cranbrook Acadelry, Eoc,heater, r Syracuse, Al'nany, Arua Arbor, Los Angetee and San I He wee born in London, Ontarlo tn ltt!, Francisco. 5 I F and currenttry iives i,n San Franclsco and london, rA 1 England. -.. v \- d ON HOLOGRAPI{Y AND A WAY TO MAKE HOLOGRAMS by J. Pethick t Cover drar*ing by Peg Bennett, based on a I sculpture by J. Pethiek 0, frlt,oplt , A"{ A BELLTOhIER BOOK ,i, 0 Belltower Enterprises, 1971