Optical glass - adomain

Concept

Amorphous(glassy)opticaldielectricmaterialthattransmitslight.Itcanbeusedtomakevariousopticalelementssuchasprisms,lenses,filters,etc.Afterthelightpassesthrough,thepropagationdirection,phaseandintensitycanbechanged.Accordingtodifferentrequirements,opticalglasscanbedividedintothreecategories:①Colorlessopticalglass-itisalmostcompletelytransparentinthevisibleandnear-infraredwideband,anditisthemostusedopticalglass.Accordingtothedifferenceofrefractiveindexanddispersion,therearehundredsofbrands,whichcanbedividedintotwovarieties,namelycrownopticalglass(representedbyK)andflintopticalglass(representedbyF).Crownglassisborosilicateglass,whichbecomesflintglassafteraddingalumina.Themaindifferencebetweenthetwoisthattherefractiveindexanddispersionofflintglassarerelativelylarge,sospectroscopiccomponentsaremostlymadeofit.②Radiationresistantopticalglass——hasallthepropertiesofcolorlessopticalglass,andcanbasicallynotchangetheperformanceunderradiationirradiation.Foropticalinstrumentsirradiatedbygamma,itsvarietyandbrandarethesameascolorlessopticalglass.Itschemicalcompositionisbasedoncolorlessopticalglass,andasmallamountofceriumoxideisaddedtoeliminatethecolorcenterformedbyhigh-energyradiationintheglass,sothatthelightabsorptionofthisglasshaslittlechangeafterbeingirradiated.③Coloredopticalglass-specificabsorptionortransmissionpropertiesforcertainwavelengthsoflight.Alsoknownasfilterglass,therearemorethanonehundredvarieties.Thecolorfiltercanselectivelyabsorbcertaincolors,andtheneutralfilterabsorbsthelightofallwavelengthsthesame,butitreducestheintensityofthebeamwithoutchangingitscolor.Theinterferencefilterisbasedontheprincipleoflightinterference,whichreflectsunwantedcolorsinsteadofabsorbingthem.

Inrecentyears,somenewtypesofopticalglasshavebeendeveloped,suchasglasswithgoodtransmittancetoinfraredandultraviolet;glasswithextremelyhighorextremelylowrefractiveindexordispersion;Glass;magneto-opticalglassinwhichthepolarizationplanerotateswhenlightpassesthroughtheglassalongthedirectionofthemagneticforce;electro-opticalglassthatproducesbirefringenceundertheactionofanexternalelectricfield,etc.

Prospects

Opticalglassisthefoundationandimportantpartoftheoptoelectronictechnologyindustry.Especiallyafterthe1990s,withthecontinuousintegrationofoptics,electronicinformationscience,andnewmaterialscience,theapplicationofopticalglassasthebasicmaterialofoptoelectronicsinthethreefieldsofopticaltransmission,opticalstorageandoptoelectronicdisplayhasadvancedbyleapsandbounds.Socialinformatization,especiallyoneofthebasicconditionsforthedevelopmentofoptoelectronicinformationtechnology.

Withthesustainedandstabledevelopmentofthedomesticeconomy,China'sopticalglassmanufacturingindustryisdevelopingrapidly.AccordingtodatafromtheNationalBureauofStatistics,in2010,thenumberofenterprisesabovedesignatedsizeintheopticalglassmanufacturingindustryreached246.Theindustry'sannualsalesrevenuewas23.405billionyuan,ayear-on-yearincreaseof53.70%;therealizedprofitwas1.537billionyuan,ayear-on-yearincreaseof87.10%;assets;Thescalereached26.45billionyuan,anincreaseof77.49%year-on-year.Sincetheopticalglassmanufacturingindustryisdominatedbydomesticsales,theimpactofthefinancialcrisisonitisrelativelysmall,andtheindustrystillshowsagoodgrowthmomentum.

Productintroduction

Glassmaterialsusedtomanufacturelenses,prisms,mirrors,windows,etc.ofopticalinstrumentsormechanicalsystems.Includingcolorlessopticalglass(usuallyreferredtoasopticalglass),coloredopticalglass,radiationresistantopticalglass,radiationprotectionglassandopticalquartzglass.Opticalglasshasahighdegreeoftransparency,ahighdegreeofchemicalandphysical(structureandperformance)uniformity,andhasspecificandpreciseopticalconstants.Itcanbedividedintosilicate,borate,phosphate,fluorideandchalcogenideseries.Therearemanyvarieties,mainlyclassifiedaccordingtotheirpositionintherefractiveindex(nD)-Abbevalue(VD)diagram.Traditionally,alltypesofglasswithnD>1.60,VD>50andnD<1.60,VD>55aredesignatedascrown(K)glass,andtheothertypesofglassaredesignatedasflint(F)glass.Crownglassisgenerallyusedasaconvexlens,andflintglassisusedasaconcavelens.Usuallycrownglassbelongstoalkali-containingborosilicatesystem,lightcrownglassbelongstoaluminosilicatesystem,heavycrownglassandbariumflintglassbelongtoalkali-freeborosilicatesystem,andmostflintglassbelongstoleadpotassiumsilicatesystem.Withthecontinuousexpansionoftheapplicationfieldofopticalglass,itsvarietyisconstantlyexpanding,anditscompositionincludesalmostalltheelementsintheperiodictable.

Aninorganicglassymaterialthattransmitslightthroughrefraction,reflection,andtransmission,orchangestheintensityorspectraldistributionoflightthroughabsorption.Ithasstableopticalpropertiesandhighopticaluniformity.

Opticalclassification

Colorlessopticalglass

Therearespecificrequirementsforopticalconstants,withhightransmittanceinthevisibleregion,nochoiceAbsorbthecharacteristicsofcoloring.AccordingtothenumberofAbbe

,itisdividedintocoronaltypeandflinttypeglass,andeachtypeisdividedintoseveraltypesaccordingtotherefractiveindex,andtheyarearrangedinorderaccordingtotherefractiveindex.Mostlyusedaslenses,prisms,mirrors,etc.oftelescopes,microscopes,cameras,etc.

Anti-radiationopticalglass

Ithasalargeabsorptioncapacityforhigh-energyradiation,includinghigh-leadglassandCaO-B2O2systemglass,theformercanpreventγ-rayandX-rayirradiation,thelattercanabsorbslowneutronsandthermalneutrons,mainlyusedinthenuclearindustry,medicalfields,etc.asshieldingandpeepingwindowmaterials.

Irradiationresistantopticalglass

Undercertainγ-rayandX-rayirradiation,thetransmittanceofthevisibleareachangesless.VarietiesandgradesSameascolorlessopticalglass,itisusedtomanufactureopticalinstrumentsandpeepwindowsunderhigh-energyradiation.

Coloredopticalglass

Alsoknownasfilterglass.Ithasselectiveabsorptionandtransmissionpropertiesforspecificwavelengthsintheultraviolet,visibleandinfraredregions.Accordingtothespectralcharacteristics,itisdividedintothreetypes:selectiveabsorption,cut-offandneutralgray;accordingtothecoloringmechanism,itisdividedintoioncoloring,metalcolloidcoloringandsulfurseleniumTherearethreetypesofchemicalcoloring,whicharemainlyusedtomanufactureopticalfilters.

Ultravioletandinfraredopticalglass

Ithasspecificopticalconstantsandhightransmittanceintheultravioletorinfraredband,andcanbeusedasultravioletandinfraredopticalinstrumentsorUsedaswindowmaterial.

Opticalquartzglass

Withsilicaasthemaincomponent,ithasthecharacteristicsofhightemperatureresistance,lowexpansioncoefficient,highmechanicalstrength,andgoodchemicalproperties.Itisusedtomanufactureprisms,lenses,windowsandmirrorswithspecialrequirementsfortransmissionofvariouswavebands.Inaddition,therearealsophotomasks,liquidcrystaldisplaypanels,andthin-plateglassusedinthemanufactureoflarge-scaleintegratedcircuits;magneto-opticalglassinwhichthepolarizationplanerotateswhenlightpassesthroughtheglassalongthedirectionofmagneticforce;lightpassesthroughinacertaindirectionAcousto-opticglasswithlightdiffraction,reflection,convergenceorlightfrequencyshiftoccurswhenultrasonicglassisused.

Dispersionclassification

Accordingtothedispersion,itisdividedintotwocategories:thecrowntype(K)withthesmallerdispersion,andtheflinttype(F)withthelargerdispersion.

①Crownopticalglassisdividedintofluorinecrown(FK),lightcrown(QK),phosphorcrown(PK),heavyphosphorcrown(ZPK),crown(K),heavycrown(ZK),Bariumcrown(BaK),lanthanumcrown(LaK),titaniumcrown(TiK)andspecialcrown(TK),etc.

②Flintopticalglassisdividedintolightflint(QF),flint(F),heavyflint(ZF),bariumflint(BaF),heavybariumflint(ZBaF),lanthanumflint(LaF),Heavylanthanumflint(ZLaF),titaniumflint(TiF),crownflint(KF)andspecialflint(TF),etc.Theyaredistributedindifferentareasintherelationalimageoftherefractiveindexndandthedispersioncoefficientv.

Anti-radiation

Anti-radiationglassisakindofgeneralizedopticalglass.Includingradiation-proofglassandradiation-resistantglass.Radiation-proofglassismainlyglassthathasalargeabsorptioncapacityforγ-raysandX-rays.Whenγ-raysorX-raysentertheprotectiveglass,thephotoelectriceffectisgeneratedinsidetheglass,positiveandnegativeelectronpairsaregenerated,andexcitedstateandfreestateelectronsaregeneratedatthesametime,sothattheenergyoftheinjectedγ-raysorX-raysisreduced,andthepenetratingpowerisreduced.,Playedaprotectiverole.

Whenthedensityofradiation-proofglassincreases,theshieldingabilityincreasesaccordingly.Thedensityoftheγ-ray-proofglassisusuallynotlessthan4.5g/cm.Inrecentyears,glasswithadensityof6.2to6.5g/cmhasbeguntobeused,andtheZFseriesarecommonlyused.

Radiation-resistantopticalglassmainlyreferstoopticalglassthatisnoteasytocolorundertheactionofgammarays.Thenamingofradiation-resistantopticalglassgradesisstillbasedontheopticalglassgrade,indicatingthenumberofroentgensthatcanwithstandradiation.Forexample,theopticalconstantofK509radiation-resistantopticalglassisthesameasK9,anditcanwithstand10roentgendosesofgammarays.Ordinaryglassgeneratesfreeelectronsafterbeingradiatedbyhigh-energyrays,whichcombinewiththevacanciesintheglasstoformacolorcenter.Atthesametime,itcanalsoshiftthenucleus,destroythenormalstructure,andalsoproduceacolorcenter,whichmakestheglasscolor.

CeO2isintroducedintotheradiation-resistantopticalglass.Afterhigh-energyγ-raysareirradiated,electronscanbetrappedduetoformula①,andnocolorcenterisgeneratedinsidetheglass.Moreover,becausetheabsorptionbandsofCeandCeareintheultravioletArea.WhentheCeO2contentistoohigh,theabsorptionbandintheultravioletandinfraredextendstothevisiblelightregion,whichincreasestheabsorptionoftheblueregionofvisiblelight,resultinginayellowishglass.Atthesametime,itwillalsodarkenthecolorduetotheinfluenceofothercomponentsintheglass,sothecontentofCeO2cannotbetoohigh.ThecontentofCeO2inK509isabout0.4%to0.5%,andthecontentofCeO2inK709isabout1%.

Makingmaterials

Usehigh-qualityquartzsandasthemainmaterial.Appropriatelyaddauxiliarymaterials.Duetothehighrefractiveindex,lowdispersionandgoodchemicalstabilityofrareearths,opticalglasscanbeproduced,whichcanbeusedtomakelensesforadvancedcameras,videocameras,telescopesandotheradvancedopticalinstruments.Forexample,akindoflanthanumglasswithexcellentopticalpropertiescontaininglanthanumoxidelao360%andboronoxideb2o340%isanindispensableopticalmaterialformanufacturinghigh-endcameralensesandperiscopelenses.Inaddition,usingtheradiationprotectionpropertiesofsomerareearthelements,radiationprotectionglasscanbeproduced.

Productionmethod

Therawmaterialsfortheproductionofopticalglassaresomeoxides,hydroxides,nitratesandcarbonates,andphosphatesorfluoridesareintroducedaccordingtotherequirementsoftheformulation.Inordertoensurethetransparencyofglass,thecontentofcoloredimpurities,suchasiron,chromium,copper,manganese,cobalt,nickel,etc.,mustbestrictlycontrolled.Wheningredientsarerequired,accurateweighinganduniformmixingarerequired.Themainproductionprocessesaresmelting,forming,annealingandinspection.

①Smelting:Therearesinglecruciblebatchsmeltingmethodandtankkiln(seekiln)continuoussmeltingmethod.Singlecruciblesmeltingmethodcanbedividedintoclaycruciblesmeltingmethodandplatinumcruciblesmeltingmethod.Nomatterwhatkindofsmeltingmethodisused,itneedstobestirredwithastirrer,andthetemperatureandstirringarestrictlycontrolledtomaketheglassliquidreachahighdegreeofuniformity.Theclaycruciblecansmeltmostcrownglassandflintglass,withlowcost,andisusedwhenthemeltingtemperatureoftheglassexceedstheservicetemperatureofplatinum.Theplatinumcruciblecansmelthigh-qualityglassthathasaseriouscorrosiveeffectontheclaycrucible,suchasheavycrown,heavybariumflint,rareearthglassandfluorophosphorousglass.Platinumcruciblesareheatedbyelectricity,generallysilicon-carbonrodsorsilicon-molybdenumrodelectricfurnacesareused.However,high-frequencyheatingcanbeusedtomanufactureglassthathasahightendencytocrystallize,requiresrapidcooling,andhascertainrequirementsontheatmosphere.

Sincethe1960s,variouscountrieshavesuccessivelyadoptedcontinuoustanksmeltinglinedwithplatinumtogreatlyincreasetheoutputandqualityofopticalglass.Thisisthemaintrendinthedevelopmentofthecurrentopticalglassproductionprocess.

②Themoldingmethodsformoldingopticalglassincludeclassicalcruciblemethod,rollingmethodandpouringmethod,butleakagemolding(usingasinglecrucibleorcontinuousmeltingtoflowoutthematerialliquid)ismoreandmorewidelyused.Itcandirectlydrawarodordropmaterialtoformalarge-sizeblank,whichimprovestheutilizationrateofthedropandtheyieldrate.

③AnnealingInordertoeliminatetheinternalstressoftheglasstothegreatestextentandimprovetheopticaluniformity,astrictannealingsystemmustbeformulatedandprecisionannealingiscarriedout.

④InspectionTheindicatorsmeasuredare:opticalconstant,opticaluniformity,stressbirefringence,streaks,bubbles,etc.

Optical glass

QualityRequirements

Thedifferencebetweenopticalglassandotherglassesisthatasanintegralpartoftheopticalsystem,itmustmeettherequirementsofopticalimaging.Therefore,thejudgmentofthequalityofopticalglassalsoincludessomespecialandstricterindicators.Therearethefollowingrequirementsforopticalglass:1.Specificopticalconstantsandtheconsistencyoftheopticalconstantsofthesamebatchofglass

Eachtypeofopticalglasshasaspecifiedstandardrefractiveindexvaluefordifferentwavelengthsoflight,asanopticaldesignThebasisfortheauthortodesigntheopticalsystem.Therefore,theopticalconstantsoftheopticalglassproducedbythefactorymustbewithinacertaintolerancerangeofthesevalues,otherwisetheactualimagingqualitywillnotmatchtheexpectedresultduringthedesignandthequalityoftheopticalinstrumentwillbeaffected.Atthesametime,becausethesamebatchofinstrumentsareoftenmadeofthesamebatchofopticalglass,inordertofacilitatetheunifiedcalibrationoftheinstruments,theallowabledeviationoftherefractiveindexofthesamebatchofglassesismorestringentthantheirdeviationfromthestandardvalue.

Second,hightransparency

Theimagebrightnessoftheopticalsystemisproportionaltotheglasstransparency.ThetransparencyofopticalglasstolightofacertainwavelengthisexpressedbythelightabsorptioncoefficientKλ.Afterthelightpassesthroughaseriesofprismsandlenses,partofitsenergyislostbytheinterfacereflectionoftheopticalpartsandtheotherpartisabsorbedbythemedium(glass)itself.Theformerincreaseswiththeincreaseoftherefractiveindexoftheglass.Forhigh-refractive-indexglass,thisvalueisverylarge.Forexample,thelightreflectionlossofonesurfaceofthecounterweightflintglassisabout6%.Therefore,foranopticalsystemcontainingmultiplethinlenses,themainwaytoincreasethetransmittanceistoreducethereflectionlossonthelenssurface,suchascoatingthesurfacewithananti-reflectioncoating.Forlarge-sizedopticalpartssuchastheobjectivelensofanastronomicaltelescope,thetransmittanceoftheopticalsystemismainlydeterminedbythelightabsorptioncoefficientoftheglassitselfduetoitslargethickness.Byimprovingthepurityoftheglassrawmaterialsandpreventinganycoloringimpuritiesfrommixingintheentireprocessfrombatchingtosmelting,thelightabsorptioncoefficientoftheglasscangenerallybemadelessthan0.01(thatis,thelighttransmittanceoftheglasswithathicknessof1cmisgreaterthan99%).

Coldprocessing

AmethodofusingchemicalvaporheattreatmentandasinglepieceofsodalimesilicaglasstochangeitsoriginalmolecularstructurewithoutaffectingtheoriginalcolorandlighttransmittanceoftheglasstoachieveUltra-hardnessstandard,ultra-hardnessfire-resistantglassanditsmanufacturingmethodandspecialequipmentthatmeetthefire-proofrequirementsunderhigh-temperatureflameimpact.Itismadeofthefollowingweightratiocomponents:potassiumsaltvapor(72%to83%),argon(7%to10%),gaseouscopperchloride(8%to12%),nitrogen(2%～6%).Itincludesthefollowingprocessflow:cuttingwithsoda-limesilicaglassasthesubstrate,andcoldprocessingoffineedgegrinding→chemicalvaporheattreatmentofthecold-workedsoda-limesilicaglass→coatingthesurfaceofthesoda-limesilicaglasswithafireprotectionfilm→Thesurfaceofsodalimesilicaglassissubjectedtospecialphysicaltemperingtreatment.Aspecialthermaldecompositiongasificationequipmentiscomposedofacylinderbody,acylinderheadfittedwithit,andareactionkettleintegrallyconnectedwiththecylinderhead.

Development

Thedevelopmentofopticalglassandthedevelopmentofopticalinstrumentsareinseparable.Newreformsinopticalsystemsoftenputforwardnewrequirementsforopticalglass,thuspromotingthedevelopmentofopticalglass.Similarly,thesuccessoftrialproductionofnewvarietiesofglassalsoofteninturnpromotethedevelopmentofopticalinstruments.

Theearliestopticalmaterialsusedtomakeopticalpartswerenaturalcrystals.ItissaidthatcrystalwasusedaslensinancientAsilia,whilenaturaltourmaline(teamirror)andcitrinewereusedinancientChina.ArchaeologistsprovedthatpeopleinEgyptandus(WarringStatesPeriod)wereabletomakeglassbeforethethirdmillenniumAD.ButtheuseofglassasglassesandmirrorsbeganinVeniceinthethirteenthcentury.Engelsgaveahighevaluationofthisinthe"NaturalDialectics",thinkingthatthiswasoneoftheoutstandinginventionsofthetime.Sincethen,duetothedevelopmentneedsofastronomersandnavigation,Galileo,Newton,Descartes,etc.alsomadetelescopesandmicroscopesoutofglass.Sincethe16thcentury,glasshasbecomethemainmaterialformanufacturingopticalparts.

Intheseventeenthcentury,achromaticopticalsystemsbecamethecentralissueofopticalinstruments.Atthistime,duetotheimprovementoftheglasscompositionandtheintroductionofleadoxideintotheglass,Hullobtainedthefirstpairofachromaticlensesin1729.Sincethen,opticalglasshasbeendividedintotwocategories:crownandflintglass.

In1768,JiNanfirstproduceduniformopticalglassbymixingwithclayrodsinFrance,andthusbegantoestablishanindependentopticalglassmanufacturingindustry.Inthemid-nineteenthcentury,severaldevelopedcapitalistcountrieshavesuccessivelyestablishedtheirownopticalglassfactories,suchastheFrenchPara-MuntuCompany(1872),theBritishChanceCompany(1848),andtheGermanSchottCompany(1848).)Wait.

Inthenineteenthcentury,therewasagreatdevelopmentinopticalinstruments.OntheeveoftheFirstWorldWar,inordertorapidlydevelopmilitaryopticalinstruments,Germanyrequiredtobreakthelimitationofthelackofopticalglassvarieties.Atthistime,thefamousphysicistAyuanparticipatedintheworkoftheSchottfactory.HeaddednewoxidessuchasBaO,B2O3,ZnO,P2O3,etc.totheglass,andstudiedothereffectsontheopticalconstantsoftheglass.Onthisbasis,bariumcrown,boroncrown,zinccrownandothertypesofglassweredeveloped,andatthesametime,specialrelativelypartialdispersionflintglasswastrial-produced.Duringthisperiod,thevarietiesofopticalglasshavegreatlyexpanded,andthereforemorecompletecamerasandmicroscopeobjectiveshaveappearedinthefieldofopticalinstruments.

Untilthe1930s,mostoftheworkwasstillcarriedoutonthebasisoftheSchottfactory.By1934,hehadobtainedaseriesofheavycrownglasses,suchasGermanSK-16(620/603)andSK-18(639/555).Sofar,itcanbeconsideredasastageinthedevelopmentofopticalglass.

BeforeandafterWorldWarII,withthedevelopmentofvariousopticalinstrumentssuchasaerialphotography,ultravioletandinfraredspectroscopyinstruments,andadvancedphotographicobjectivelenses,newdemandsforopticalglasswerecreated.Atthistime,opticalglasshascorrespondinglydevelopednewdevelopments.In1942,scientistsinMoreyintheUnitedStatesandlaterintheSovietUnionandGermanysuccessivelyintroducedrarefiedoxidesandscatteredoxidesintotheglass,thusexpandingtheglassvarietiesandobtainingaseriesofhigh-refractive-indexandlow-dispersionopticalglasses.SuchasGermanLaK,LaF,SovietUnionCTKandТЬФandothervarietiesseries.Atthesametime,researchonlow-refractive-indexandlarge-dispersionglasshasalsobeencarriedoutandaseriesofopticalglasseswithfluorotitanicsilicatesystemhavebeenobtained,suchastheSovietUnionЛФ-9,ЛФ-12,GermanF-16andothervarieties.

Becausetherearemoreorlessdefectsintheprocessingoruseperformanceofvariousnewtypesofopticalglass,whileresearchingandexpandingthefieldofopticalglass,italsoaimstoimprovethephysicalpropertiesofvariousnewtypesofopticalglass.Andphysicochemicalproperties.Andtheproductionprocesshasdonealotofwork.

Summarizingtheabovehistoricaldevelopmentprocess,itcanbepredictedthatthefuturedevelopmentdirectionofopticalglassis:

①Makingparticularlyhighrefractiveindexglass;

②Obtainspecialrelativelypartialdispersionglass;

③Developinfraredandultravioletopticalglass;

④ReplacesomeundesirablecomponentsinglasssuchasradioactiveTHO2,toxicBcO,Sb2O3,etc.；

⑤Improvethechemicalstabilityofglass;

⑥Improveglasstransparencyandpreventglassradiationcoloring;

⑦Improvetheprocessandreducethepriceofnewvarietiesofglass.

Rareearthelements

Inthe1930s,anewrareearthelementopticalglassappeared,themaincomponentsofwhichareoxidesoflanthanum,thoriumandtantalum.Therareearthelementopticalglasshasahighrefractiveindex,whichopensupnewpossibilitiesforthedesignofopticallenses.Lanthanumglassisoftenfoundinlarge-aperturelensestoday.Theproductionofthoriumglasshasbeendiscontinuedduetoradioactivity.Lead-freeopticalglass

Lead-freeopticalglassdoesnotcontainleadandarsenic,andismarkedwithN.

Classificationofopticalglass

GlasseswithsimilarchemicalcompositionandopticalpropertiesarealsodistributedinadjacentpositionsontheAbbediagram.TheAbbediagramhasasetofstraightlinesandcurves,whichdividetheAbbediagramintomanyareastoclassifytheopticalglass;suchascrownglassK5,K7,K10intheKarea,andflintglassF2,F4,F5intheFarea.Symbolsinthenameoftheglass:

Fstandsforflint

Kstandsforcrownplate

Bstandsforboron

BAstandsforbarium

LAstandsforlanthanum

Nstandsforlead-free

Pstandsforphosphorus

Physicalparametersofopticalglass

VdAbbeCountfoursignificantfigures

ndrefractiveindexsevensignificantfigures

Vefoursignificantfigures

nesevensignificantfigures