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headerforSPIEuseHowtoselectnonlinearcrystalsandmodeltheirperformanceusingSNLOsoftwareA.V.SmithSandiaNationalLaboratories,MS1423,Albuquerque,NM87185ABSTRACTSNLOispublicdomainsoftwaredevelopedatSandiaNat.Labs.Itisintendedtoassistintheselectionofthebestnonlinearcrystalforaparticularapplication,andinpredictingitsperformance.Thispaperbrieflydescribesitsfunctionsandhowtousethem.Keywords:opticalparametricmixing,opticalparametricoscillator,nonlinearcrystals,nonlinearopticssoftware1.INTRODUCTIONTheadventofpowerfuldesktopcomputershasmadeitpossibletoautomatecalculationsofthelinearandnonlinearpropertiesofcrystals,andtoperformdetailedsimulationsofnonlinearmixingprocessesincrystals.ThepurposeofSNLOistomakethesecalculationsavailabletothepublicinafree,user-friendly,windows-basedpackage,withthehopethatthiswilladvancethestateoftheartinapplicationssuchasopticalparametricoscillators/amplifiers(OPO/OPA),opticalparametricgeneration(OPG),frequencydoublers,etc.TherearethreetypesoffunctionsincludedintheSNLOmenu,showntotheright.Thefirstsethelpincomputingthecrystalpropertiessuchasphase-matchingangles,effectivenonlinearcoefficients,groupvelocity,andbirefringence.TheyincludefunctionsRef.Ind.,Qmix,Bmix,QPM,Opoangles,andGVM.Thesecondset,functionsPW-mix-LP,PW-mix-SP,PW-mix-BB,2D-mix-LP,2D-mix-SP,PW-OPO-LP,PW-OPO-SP,PW-OPO-BB,and2D-OPO-LP,modeltheperformanceofnonlinearcrystalsinvariousapplications,andthethirdset,Focus,Cavity,andHelp,arehelperfunctionsfordesigningstablecavities,computinggaussianfocusparameters,anddisplayinghelptextforeachofthefunctions.Thecapabilitiesofselectfunctionsarepresentedbelow.2.CRYSTALPROPERTYCALCULATIONS2.1Selectingangle-tunedcrystalsThefunctionQMIXisthebeststartingplaceforselectinganonlinearcrystalforyourapplication.Whenyouselectacrystalfromthelistof40+crystals,theviewingareawilldisplayitsproperties,includingthetransmissionrange(asaplotiftheinformationisavailable),referencesforSellmeierdata,nonlinearcoefficients,damagethresholds,etc.Enterthewavelengthsforyourmixingprocessandpushthe‘Run’buttontocomputeinformationspecifictoallpossiblephase-matchedprocessesfortheselectedcrystalatthespecifiedwavelengths.Thefiguretotheleftshowsoneexample.NotethatforbiaxialcrystalsonlytheprincipalplanesareallowedinQMIX.Ifyouarecuriousaboutabiaxialcrystal’spropertiesoutsidetheprincipalplanes,youcanexplorethemusingBMIX.Furtherinformationoncrystalpropertiesisavailableinthepaperslistedinthebibliography‘Crystals.pdf’includedwithSNLO.Itreferencesover600papersrelatingtononlinearopticalcrystals.2.2Selectingquasiphase-matchedcrystalsThefunctionQPMhelpsyoufindtherightquasiphasematchedpolingperiodforanyofthepopularquasiphasematchablecrystals.Italsocomputestemperatureandpumpwavelengthtuningpropertiesforthecrystal.Youcanchosethepolarizationsforyourprocessesaswell,althoughthezzzpolarizationisusuallytheoneofpracticalinterest.2.3Selectingangle-tunedOPOcrystalsAsshownbelow,thefunctionOpoanglesdisplaysaplotofthesignal/idlerwavelengthversuscrystalangleforagivenpumpwavelength.Italsocomputesthenonlinearcoefficientandtheparametricgainversusangle.ComparinggainoverthewavelengthrangeofinterestbetweendifferentcrystalsandphasematchingtypesgivesagoodindicationofrelativeOPOperformance.Notethatthisfunctionpermitsnoncollinearphasematching.Clickingonthe‘pumptilt’editboxdisplaysadiagramofthenoncollinearangles.ThesignalisassumedtoremainalignedtothecavityofanOPO,thepumpistiltedbyafixedanglerelativetothesignalwhilethecrystalandidlertiltbyvariableamountstoachievephasematch.2.4Computingacrystal’slinearopticalpropertiesThefunctionRef.Ind.canbeusedtocomputerefractiveindices,groupvelocities,groupvelocitydispersions,andbirefringentwalkoffforagivenpropagationangle,temperature,andwavelength.Thisisusefulifyouwanttomakeyourowncalculationsofphasematching,groupvelocitymatching,etc.2.4Computinggroupvelocityinangle-tunedcrystalsThefunctionGVMcomputesthephasematchinganglesandgroupvelocitiesfornoncollinearphasematching.Theslantparameterspecifiestheanglebetweenthepump(bluest)wave’spulseenvelopeanditsk-vector.Allthepulseenvelopesareassumedtohavethesameorientationsoiftheyareallgroupvelocitymatchedthereisnotemporal(longitudinal)walkoff,butthereisspatial(lateral)walkoff.Forasetofwavelengthsandpolarizations,therelativegroupvelocitiescanbevariedbychangingthevalueoftheslant.Inmanycasesitispossibletoachieveperfectgroupvelocitymatchinginthisway.Thishasobviousapplicationinfsmixing,butitcanalsobeusedinmixingbroadbandlightwithtemporalstructureonafsorpsscale.3.NONLINEARMIXINGMODELS3.1Modelingsingle-passmixingThefunctionswith‘mix’intheirtitlehandlesingle-passmixing,asopposedtomixinginanopticalcavity.Thefunctionswiththe‘PW’prefixmodelplane-wavemixing,thosewiththe‘2D’prefixincludeGaussianspatialprofileswithdiffractionandbirefringentwalkoff.Theplane-wavemodelsrunmuchfasterthanthe‘2D’models,sotheycanbeusedtoarriveatanapproximatesetofconditionsthatcanthenbefinetunedwiththediffractivemodels.Thefunctionswithsuffix‘LP’ignoregroupvelocityeffectsandareappropriateformonochromaticnsandlongerpulses,orformonochroma