Application Note by QUANTELQUANTEL 1/7 Distribution: external EYLSA laser for atom cooling

For decades, cold atom system and Bose-Einstein condensates (obtained from ultra-cold atoms) have been two of the most studied topics in fundamental physics. Several Nobel prizes have been awarded and hundreds of millions of dollars have been invested in this research. In 1975, cold atom research was enhanced through discoveries of laser cooling techniques by two groups: the first being David J. Wineland and Hans Georg Dehmelt and the second Theodor W. Hänsch and Arthur Leonard Schawlow. These techniques were first demonstrated by Wineland, Drullinger, and Walls in 1978 and shortly afterwards by Neuhauser, Hohenstatt, Toschek and Dehmelt. One conceptually simple form of Doppler cooling is referred to as optical molasses, since the dissipative optical force resembles the viscous drag on a body moving through molasses. Steven Chu, Claude Cohen-Tannoudji and William D. Phillips were awarded the 1997 Nobel Prize in Physics for their work in “laser cooling and trapping of neutral atoms”. In 2001, Wolfgang Ketterle, Eric Allin Cornell and Carl Wieman also received the Nobel Prize in Physics for realization of the first Bose-Einstein condensation. Also in 2012, Serge Haroche and David J. Wineland were awarded a Nobel prize for “ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems”. Even though this award is more directed toward photons studies, it makes use of cold atoms (Rydberg atoms).

Laser cooling Principle Sources: https://en.wikipedia.org/wiki/Laser_cooling and https://en.wikipedia.org/wiki/Doppler_cooling

Laser cooling refers to a number of techniques in which atomic To a stationary atom the laser is neither red- and molecular samples are cooled to near absolute zero through nor blue-shifted and the atom does not absorb interaction with one or more laser fields. All laser cooling the photon. techniques rely on the property that when an object (usually an atom) absorbs and re-emits a photon (a particle of light) its To an atom moving away from the laser momentum changes. The temperature of a substance is higher the beam is red-shifted and the atom does not when there is a larger distribution of the velocities of the particles absorb the photon. that make up the substance. Laser cooling techniques combine To an atom moving towards the laser the beam atomic spectroscopy with the previously mentioned mechanical is blue-shifted (at its atomic transition wavelength) effect of light to compress the velocity distribution of a group of and the atom absorbs the photon, slowing it. particles, thereby cooling the particles. The absorbed photon excites the atom, The first example of laser cooling, and also the most common moving an electron to a higher quantum state. method (so much so that it is often simply referred to as 'laser cooling') is Doppler cooling (see Figure). The atom re-emits a photon, but the direction Doppler cooling uses a laser slightly red-shifted from the of the photon is random, so no net change molecule’s atomic transition with the result that: in momentum results over many absorption-emission cycles. Copyright © Quantel. All Rights Reserved. ANI001-version A. Quantel reserves the right to make changes without prior notice. A. ANI001-version All Rights Reserved. Copyright © Quantel. C i ht © Q t l All Ri ht R d AN001 i A Q t l th i ht t k h ith t i ti

[email protected] Application Note by QUANTELQUANTEL 2/7 Distribution: Internalexternal only EYLSA laser for atom cooling

Cooling atoms requires the photon absorption/emission cycle EYLSA fiber laser previously described to be reproduced a large number of times. Photons emitted by a laser source have the same direction. After a Wavelength coverage large number of absorption/emission cycles, the total force EYLSA fiber lasers are available at different wavelength covering: received by an atom resulting from absorption is equal to the sum • infrared (15XX and 10XX nm), of the force applied from each absorption multiplied by the number • near-IR (7XX nm), of absorptions. Whereas the total force applied to an atom • green (5XX nm) ranges. resulting from spontaneous emissions is quasi null (due to the random direction of photon emissions). Other wavelengths are currently under development. For this to happen, it is necessary that the atoms recover their (See graph 1 page 6) initial fundamental state through spontaneous emission in order to be excited again and so on. This is called cycling transition. Some Wavelength accuracy and stability atoms have a more complex structure, composed by 2 or more EYLSA wavelength accuracy may be specified at +/-0.01 nm using wavelength meters or atomic cells. energy levels within the atom (hyperfine structure), and may require the use of more than one cooling laser (see D2 transition of Frequency stability obtained from EYLSA 780 nm, wavelength locking the Rb structure). loop open. (see graph 2 page 6).

F = 3 gF o=o2/3 Cooling (0.93 MHz/G) 193.7407(46) MHz 266.6500(90) MHz

2 5 P 3/2 72.9112(32)72.9 MHz F = 2 gF o=o2/3 229.8518(56) MHz (0.93 MHz/G) 302.0738(88)88) MHz 156.9470(70) MHz

F = 1 gF o=o2/3 72.2180(40) MHz (0.93 MHz/G) F = 0

780.241 209 686(13) nm Repumping 384.230 484 468 5(62) THz 12 816.549 389 93(21) cm -1 1.589 049 462(38) eV

F = 2 gF o=o1/2 (0.70 MHz/G) 2.563 005 979 089 109(34) GHz

2 5 S1/2 6.834.83 682 610 904 290(90) GHz

4.271 676 631 815 181(56) GHz

F = 1 gF o=o-1/2 (-o0.70 MHz/G) Figure 1: D2 line of Rb87 and cycling transition Copyright © Quantel. All Rights Reserved. ANI001-version A. Quantel reserves the right to make changes without prior notice. A. ANI001-version All Rights Reserved. Copyright © Quantel.

[email protected] for atomcooling EYLSA laser [email protected] 2.5 that ispreciselyshiftedfromthetargetcyclingtransition(typicallyat Doppler coolingrequireslasersthatemita Distribution: external Noteby Application are optical signaltonoise warm otheratomsbycollisions.Forthissamereasonthelaser’s insensitive totheapparatusandwon’t becooledandmayeven photons. Atomsexcitedatanothertransitionmaybecome avoid excitationofotheratomictransitionswithout-of-band lower thantheatomictransitionforbetterphotonefficiencyandto transition duringlongtimeperiods.Also, this case,4retro-reflectedbeamsarerequired. Note: circular polarizationafterthequarter-wave plate. power fluctuation(duetopolarizingoptics)andprovidegood beam polarization direction, thepolarizationneedstobesetcircularly. The force onlyonatomsthatmovetowardsthelaserpropagating direction andwithinthe2propagatingpaths.Inordertoexert a For thistrap,6beamsarerequiredtotraptheatomsineachspatial Magneto-Optical Trap (3DMOT). from thecenterofchamber. Thistypeoftrapiscalled3D will exertarestoringforceproportionaltotheatom’s distance from thetransitionwavelengthassociatedwiththismagneticfield shift theatom’s hyperfinestructures.Thus,lasersslightlyshifted chamber center. Thepurposeofthemagneticfieldistoslightly center andincreaseproportionallytothedistancefrom magnetic fieldisdesignedtobe0attheexperimentchamber cooling principleorientedin3directionsandamagneticfield.The trapping theatomsinavacuumchamberandcombininglaser In practice,anatomiccloudofmKtemperatureisobtainedby by feworders,forexamplekHztoHzlinewidthmaybenecessary. developed inmanylabs),laserlinewidthisrequiredtobenarrower measurement techniquesusingcoldatomswhichhavebeen Note: spontaneous emission). locking than thetransitionlinewidth(~MHz).Mostoftime,a atom speeds).Thespecifiedwavelengthaccuracymustbebetter linewidth ofthetransition;shiftheightisdeterminedbyinitial Γ redshiftedforoptimalatomcoolingwhere no Foratominterferometryexperiments(precision 2D MOTalsoisusedtoconcentrateacoldatombeam.In

parasitic laserlines(mode-hop) systemisrequiredtoreferencethelaseratomic requires anexcellentextinctionratiotoavoid

ratio

QUANTELQ U must beexcellent.(Thisrequiresthere A N T E L and verylimited very precisewavelength laser linewidth Γ isthenatural wavelength amplified mustbe laser fibered outputand>20dBforfreespaceoutput. output type,polarizationextinctionratiosvarybetween>17dBfor EYLSA fiberlasershavepolarizedoutputasstandard.Dependingon Polarization for astandardfrequencydoublelaser. (seegraph3page6). Optical signaltonoiseratio(OSNR)ismeasuredatbetterthan55dB rangeof20GHz,anyphotonoutsidethisisfilteredout. Periodically-poledcrystalshavealimitedspectralacceptance • conversionefficiencyis. incidentpower. Thehighertheincidentpower Second-harmonic generationisanon-lineareffectcomparedto • periodically-poled crystals. EYLSA fiberlasersgeneratevisiblelightfromIRusing Optical signaltonoiseratio overthelifecycle. Noneedtopushthecurrentup keepaconstantoutputpower • fiber Noneedforfiberinjection(thephotonisalreadyinjectedintothe output) • Noneedformodefiltering • the experiment: Each photongeneratedfromanEYLSAproductisfullyavailablefor Fully availableoutputpower the0GflightICEexperiment,Bordeaux(20parabolas) inhighvibrationandtemperaturefluctuationconditionssuchas • inlabconditionsforlongerthan2weeks • Successful long-termlockinghasbeendemonstratedwithoutrelocking: (notincludedwithEYLSA)tolocktheEYLSAfiberlaserwavelength. connectedtosaturatedabsorptionequipmentassociatedwithPID reproducibleandmode-hop-free(MHF)range.Thisinputmaybe diodepowersupplycurrent.Wavelength istunableona awavelengthlockinginput(BNC)whichdirectlymodifiesseeder • notprovidedwithEYLSA). saturatedabsorptionscheme(standardcoldatomlabapparatus, • amonitoringfiberoutputthatmaybedirectlyconnectedto EYLSA fiberlasersembed: Wavelength locking 3/7

Copyright © Quantel. All Rights Reserved. ANI001-version A. Quantel reserves the right to make changes without prior notice. for atomcooling EYLSA laser [email protected] nK temperatures.Theselasersrequirevery trapped inthisdipolepotentialtobefurthercooledhundredsof using anelectro-magneticfieldfromthelaser. Coldatomsare away fromthecyclingtransition.Adipolepotentialiscreated trapping requiresadditionallaserswithemittingwavelengths available usingelectro-magnetictrapsorhybridtraps).Dipolar optical dipolartrappingtechniques(otherare Temperatures colderthantensofμKmaybeobtainedusing (warming). paramount factorsinavoidingfluctuationofthecoldatomiccloud high outputpower, and For 3DMOT, the Distribution: external Noteby Application resetting oftheexperimentalsetup. pointing stability obtain accurateorreproduciblemeasurements. vibration andtemperaturerangeisnecessaryforalongperiodto compromise theentireexperiment.Wavelength stabilityovera reliability complex experimentalsetups.Thefirstconsiderationisthe Other laserparametersmustbeconsideredwhenusingsuch beam quality. Typical wavelengthsare1064nmand1560nm. 3D MOTschematic Figure 2 : . Inanexperimentusingseverallasersonefailuremight laserpowerstability also reducestimeconsumingbeampath

excellent beampointingstability QUANTELQ U A N T E L and lowintensitynoise beam quality Excellent beam laser and are , single modefiberdelivery. EYLSA fiberlasersbeampointingstabilityisunsurpassedduetoits Beam pointingstability on alargefrequencyband.(seegraph5page6). due tothesinglefrequencyoperation.Typical valuesarebelow0.1% EYLSA fiberlasersdeliverexcellentrelativeintensitynoiseresults Relative intensitynoise wavelength). mode fiberdelivery(standardfor780nm,optionalother EYLSA fiberlasershaveTEM00,M²<1.2output.Alsotheyoffersingle Beam quality hours ofoperation.(seegraph4page6). EYLSA fiberlasershavelessthan2%outputpowerinstabilityover12 order todeliverstablelaseroutputpower. automatically adjuststhepumpingdiodepowersupplycurrentin EYLSA fiberlaseroutputiscontrolledbyphotodiode.Afeedbackloop Output powerstability 4/7

Copyright © Quantel. All Rights Reserved. ANI001-version A. Quantel reserves the right to make changes without prior notice. for atomcooling EYLSA laser [email protected] environmental conditions stability aswellmore and morelikelytorequireasystemwithbetter atomic clocks,gravimeters,inertialsensors,etc.Usersaremore Atom coolingapplicationsarethebasisofmostaccurate Figure 3:Typical opticaltableforRbatomcoolingexperiments Distribution: external Noteby Application Figure 2 :3DMOTschematic compactness

thanarepresentwithinalab. QUANTELQ U A N T E L andfunctionalityin reliability harsher and during take-off,landingandparabolas). tested byoperationin0Gflight(0to2acceleration,highvibrations in labconditions.Theirinsusceptibilitytovibrationshasalsobeen 5-35°C beforefinalcharacterizationtovalidatetheirabilityoperate EYLSA fiberlasersundergoburn-intestsandthermalcyclingbetween Environmental conditions optical table. there isnoneedtointegratethefulllaseronavibration-damped are neededtobereadyforusewithyouropticaltable.WithEYLSA power supplytosecondharmonicgenerator. Onlyoutputconnectors The EYLSAfiberlaserall-in-onepackagecontainseverythingfromthe Compactness lasers arewarrantiedfor2years. has beenevaluatedtobebetterthan100Khours.EYLSA780fiber submitted tolong-termtestingatQuantel.Meantimebeforefailure EYLSA fiberlasersuseindustrialgradecomponentswhichhavebeen Reliability 5/7

Copyright © Quantel. All Rights Reserved. ANI001-version A. Quantel reserves the right to make changes without prior notice. for atomcooling EYLSA laser [email protected] Distribution: external Noteby Application 2: 1: better than40dB(limitedbymeasurement). measured usinghotatomsbyINLN,Nice,France.Theratiowas Note: 3: 10 20 10 0 1 3 0 1 3 EYLSAlaserwavelengthstability(unlocked). EYLSAlaserwavelengthcoverage. EYLSAlaseropticalspectrum(780nm). 450 LAlil(8 ) 80 ( l i l YLSA Opticalsignaltototalintegratedopticalnoisehasbeen 550 650 750 8508

950 QUANTELQ 0 U A 1 050 N T 1 150 E L 1 250 1 350 WAVELENGTHWA (nm) 1 450 1 550 >< 1 650

OUTPUT POWER (W) >< 4: 10 Wfiberlaser. 5: EYLSAlaseroutputpowerstability. EYLSAlaserrelativeintensitynoiseobtainedfroma1064nm,

RIN (dB/Hz) Frequency (kHz) 6/7

Copyright © Quantel. All Rights Reserved. ANI001-version A. Quantel reserves the right to make changes without prior notice. for atomcooling EYLSA laser [email protected] Laser coolingtechnologies(basedon780nm) Distribution: external Noteby Application LASER TECHNOLOGIES COMPARISON FORRb ATOM COOLING 3 2 1 Highpower532nmpumpinglaser Beginningoflife,withoutmodefiltering Warrantied powerwithexcellentbeamqualityandoutofsinglemodefiber Extra (single mode,singlefrequency) Available outputpower edainet/cenn e e Yes Yes Yes Need alignment/cleaning uaiiy+++++++ +++ +++ Tunability aaeesED CLT Ti:Sa ECDL+TA ECDL Parameters sg ot+ - + + + ++ ++ + ++ ++ ++ + ++ +++ - ++ + - + ++ ++ + +++ + ++ Usage cost Ease ofuse Reliability Output powerstability Wavelength stability Beam pointingstability Beam quality Linewidth inlt os ai +-+++ - ++ Price Signal tonoiseratio arnyOnlyelectronic Warranty

QUANTELQ U A N T E L wavelengthatsametime Repumpingandcooling • • Fiber output, FIBER LASER 2 years 1 W +++ +++ +++ +++ +++ +++ +++ +++ No ++ ++ + 1 is warrantied12months . 3.5 W 0.1 W +++ is warrantied12months (50% loss) formodefiltering • Fiber injection (15% losses) • Isolation required Only electronic Modularity 3 W +- ++ 2 3 months 3 7/7

Copyright © Quantel. All Rights Reserved. ANI001-version A. Quantel reserves the right to make changes without prior notice.