Opticalabsorptionandionizationofsilicateglasses

LeonidB.Glebov SchoolofOptics/CREOL,UniversityofCentralFloridaOrlando,FL ABSTRACT Intrinsic,extrinsic(transitionmetalsandhydroxyl),andinduced(colorcenters)absorptionofmulticomponentsilicateglasses inUV,visibleandnearJRspectralregionsaredescribed.Parasiticeffectsinfluencingabsorptionmeasurementsare discussed.Excitationtotheintrinsicabsorptionbandresultsinintrinsicluminescenceandionizationfollowedbycolorcenter generationandphosphorescence.ThethresholdsofelectronandholemobilityinglassnetworkarefoundinthefarUV region.Thehole-centersgenerationasacriterionofsubstanceionizationisproposed.Anumberofnonlinearmechanismsof glassionizationarediscussed.Two-photonionizationwasdetectedinalkaline-silicateglassesexposedtohigh-powerlaser radiationinnano-andpicosecondregimes..Three-photonionizationwasdetectedinlead-silicateglasses.Noreliabledataon multiphotonionization(withnumberofphotonsmorethan3)ofglassesarefound.Two-andthree-photoncooperativeself- multiplicationofcolorcenterswasfoundinCuC1-dopedglasses.Glassmatrixionizationbyspectralbroadeningof femtosecondJRpulsesisdescribed.Thermalandsurfaceionizationofglassunderintenseirradiationbypulsedlasersis described. 1.INTRODUCTION Anextensiveuseofpowerfullaserradiationinsuchareasasmilitaryandcivilianopticalcommunicationanddatastorage, laserprocessingofdifferentmaterials,photolithography,ctsmoreandmoreattentiontotheproblemofstabilityof opticalmaterialsunderintensiveopticalillumination.Silicateglassesarestillthemaincomponentsofthemostofoptical devicesandthereforetheirdurabilityisofhighimportanceforthementionedapplications.Theproblemofinteraction betweenintensiveopticalradiationandmatterisusuallyconnectedwithdifferentthermaleffectsanddifferenttypesof photoionization.Thehistoryoftheresearchinthisdirectionisratherlongandcountshundredsofpublicationsdedicatedto featuresofopticalabsorption,photoinducedphenomena,andlaser-induceddamageofsilicateglasses.Thispaperisdirected tothesurveyofpublicationsdealingwithlinearandnonlinearintrinsicphotoionizationofsilicateglassesastheultimate mechanismsprovidingtheupperlimitofdurabilityofglassesusedunderintenseopticalillumination.Themainpartof discussedresultswasperformedbyresearchteamsatVavilovStateOpticalInstituteatSt.Petersburg,Russia,SolidState PhysicsInstituteattheStateUniversityofLatvia(Riga,Latvia),andCenterforResearchandEducationinOpticsandLaser attheUniversityofCentralFlorida,Orlando,Florida,theUSA. Theproblemofinteractionofopticalradiationwithlightisusually ConcentrationEmptylevelsconsideredintheframeofexcitationofdifferentelectronicstatesin _________ acondensedmatterinaccordingwithenergyzonediagram.The traditionalapproachisbasedonconsiderationofelectronstatesin valenceandconductionbandsalongwithlocalizedstatesof impuritiesanddefectsincrystallinelattice.Excitationofelectrons fromvalencebandorgroundstatesofimpuritiesordefectscreates mobileelectronsintheconductionband.Electronandhole Localized migrationfollowedbytrappingorrecombinationisthebasisforthe statesBandgap mainabsorptionbandsareverysimilarincrystallineandvitreous Occupiedlevels mostpartofphotoinducedprocesses.Itisimportanttonotethat chemicalbondinginglassesisverysimilartothatoneincrystalsof thesamecomposition.Thisiswhypositionsandstructureofthe modificationsofeachmaterial.Themostimportantdifferencefor glassesisthesignificantlylowermobilityofchargecarriers.This ____________________________________________ differenceiscausedbyanumberoflocalizedlevelsintherangeof Fig.1.Energydiagramofelectronstatesinglass thebottomofconductionbandinglasseswhichisshowninFig.1 forthedielectricvitreousmatter.ThistheoreticalbackgroundstartedwithMott'sworksat60's',isthepowerfulapproach fortheanalysisofopticalpropertiesandphoto-stimulatedphenomenainglasses.Itisimportanttoemphasizethatlocalized statesinabandgapofvitreousmattercoveronlythesmallareaclosetothebottomoftheconductionbandbutdonotspread outfartothebandgap(swhywateristransparent). Electron mobility threshold Laser-Induced Damage in Optical Materials: 2000, Gregory J. Exarhos, Arthur H. Guenther, Mark R. Kozlowski, Keith L. Lewis, M. J. Soileau, Editors, SPIE Vol. 4347