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1、TimeResolvedStudyofFemtosecondMicrofabricationInSilicaGlassHiroakiMisawaa,SauliusJuodkazis,aAndriusMarcinkeviãius,bMitsuruWatanabe,aVygantasMizeikis,bandShigekiMatsuo,aaDepartmentofEcosystemEngineering,TheUniversityofTokushima,2-1Minamijyosanjima,Tokushima770-8506,JapanbLaboratoryofNano-Photoni
2、cMaterials,TheUniversityofTokushima,2-1Minamijyosanjima,Tokushima770-8506,JapanABSTRACTWereportinvestigationoflight-induceddamagethreshold(LIDT)inpurifiedsilica(transmissionbanddownto160nm)by350fslaserpulsesatthewavelengthof795nmand498nm.FocusingasinglepulsebyahighnumericapertureNA=1.35microsco
3、peobjectivelensresultsinoneofthelowestsingle-shotbulkLIDTvaluesreportedsofar,5J/cm2,whilethesurfaceablationthresholdis2.5J/cm2withbothvaluesbeingwellbelowthecriticalself-focusingpowerinsilica.Furthermore,wereportthepeculiaritiesofdamagebytwo-pulseirradiation(durationofeachpulseis440fs),wherebot
4、hpulseshaveenergiesatthelevelof0.5xLIDT.Comparisonbetweentheexperimentaldataandnumericsimulation,whichtakesintoaccountopticalfree-carriergenerationandrelaxation,demonstratesthattheseprocessescanexplainthemeasuredself-focusing,super-continuumgeneration,andlight-induceddamagethresholdvalues.Wearg
5、uethatuseofhighnumericapertureobjective,despitesubstantialtemporalpulsestretching,resultsintightfocusingwhichiscapableofovercomingthebeamself-focusing,andtheresultingfabricationqualityiscomparabletothatobtainedusingshorterpulses.Keywords:lasermicrofabrication,light-induceddamagethreshold,silica
6、1.INTRODUCTIONThree-dimensionalmicrostructuringinthebulkoftransparentmaterialsbyhighintensityfslaserpulsestypicallyusesopticalmicroscope,whichproducesstronglyfocusedlaserbeams.Underthesecircumstanceslight-materialinteractiondiffersstronglyfromthatencounteredinthecaseofsurfacelaserablation.Onepa
7、rticularissue,importantformakingthefemtosecondfabricationmorepracticalandcost-effectiveisthereductionofthephoto-modificationintensitythreshold.Toclarifythisissue,andfullyexploitthepossibilitiesof3Dfabrication,thedynamicsofdielectr