DIODELASERATOMICSPECTROSCOPY By TYEEDBARBER ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1992 UNIVERSITYOFFLORIDALIBRARIES Copyright1992 by TyeEdBarber ACKNOWLEDGEMENTS I thank myparents fortheir support and their guidance, and foralways stressingtheneedforhighereducation. Ialsothankmybrothers,WadeandBart, foreverythingtheyhavedoneforme. Iwouldliketoacknowledgemyresearchadvisor,Dr.JamesD.Winefordner, forgivingmefreedomtopursuetheworkdescribedinthisdissertation. Ihavebeen fortunateenoughtoworkwithseveralpostdocs: PietWalters, KinNg,andNico Omenetto. Theyhaveallgreatlyinfluencedme. Ihavealsohadtheopportunity toworkwithseveralfellowstudents: PaulJohnson,AbdallaAli,MikeWensing, SteveLehotayandKimberlyFerrell. IwouldespeciallyliketothankNormaAyala,whohashelpedmeprepare many ofmy presentations, papers, and this dissertation. Without her constant encouragementandhelp,muchofmyworkwouldnothavebeencompleted. iii TABLEOFCONTENTS page ACKNOWLEDGMENTS iii LISTOFTABLES vi LISTOFFIGURES vii ABSTRACT x CHAPTERS 1. INTRODUCTION 1 2. DIODELASERS 4 Introduction 4 SemiconductorMaterials 4 DiodeLaserCharacteristics 10 SpectralCharacteristics 11 LaserDiodeAgingandFailure 24 3. THEORYOFATOMICABSORPTIONAND ATOMICFLUORESCENCE 26 Introduction 26 SpectralLineProfiles 29 MethodsofMeasuringAtomicAbsorption 33 AtomicFluorescence 37 4. DIODELASERATOMICABSORPTION 39 Introduction 39 Experimental 44 ResultsandDiscussion 56 5. DIODELASERATOMICFLUORESCENCE 61 Introduction 61 Experimental 62 ResultsandDiscussion 70 EVALUATIONOFABSOLUTENUMBER 6. DENSITIESBYDIODELASERATOMIC SPECTROSCOPY 73 Introduction 73 Theory 76 CaseA 80 CaseB 81 CaseC 82 Experimental 86 ResultsandDiscussion 93 7. CONCLUSIONS 105 APPENDIXQUALITATIVECOMPARISONOFTHE SPECTRALPROFILEOFARUBIDIUM HOLLOWCATHODELAMPAND RUBIDIUMABSORPTIONINAFLAME 108 Experimental 109 ResultsandDiscussion 115 REFERENCES 121 BIOGRAPHICALSKETCH 125 LISTOFTABLES page 2-1. EquipmentUsedtoMeasuretheEmission SpectrumofaDiodeLaser 15 4-1. DetailedListofEquipmentUsedinAAS 45 5-1. DetailedListoftheEquipmentUsed 63 6-1. RelationshipofPhotodiodeSignaltothe IntegratedIntensityoftheLaserBeam 79 6-2. PartialListofEquipmentUsedfor AbsoluteAAS(SeeTable4-1for OtherEquipment) 91 A-l. ExperimentalEquipmentforMeasurement ofHyperfineStructureofRbinaHollow CathodeLampandaFlame 110 vi LISTOFFIGURES page 2-1. EnergyLevelDiagramofaSemiconductorMaterial 6 2-2. ADiagramShowingtheEllipticalBeamEmitted fromaDiodeLaser. 13 2-3. SpectrumofaMitsubishiML4402 SemiconductorLaser. 17 2-4. SchematicDiagramofExperimentalSetup UsedtoMeasuretheEmissionSpectrum ofaDiodeLaser 19 2-5. SpectrumofaMitsubishiML4402 SemiconductorLaser. TheCentralMode oftheLaserHasBeenCompletelyAbsorbed byanAtomicVaporFilterorCell 21 2-6. AGraphicalRepresentationofaTuningCurve ofaDiodeLaser.TheLocationoftheMode HopsDependsontheDirectionofTuning 23 3-1. AGraphicalRepresentationofan AbsorptionProfile 28 3-2. APlotoftheAbsorptionFactor,a, VersusFrequency 36 4-1. BlockDiagramoftheExperimentalSetup 47 4-2. DrawingShowingaSinusoidalModulationRamp. TheRampisSuperimposedonTopoftheBase Driving. InOn/OffModulation,theLaseris ModulatedOntoOnlyPartoftheAbsorption Profile. InAcrossModulation,theLaseris ModulatedAcrosstheEntireAbsorptionProfile 49 vii 4-3. OscilloscopeTracesShowingtheModulation Ramp(UpperTrace),theAbsorptionSignal (MiddleTrace),andtheReferenceWaveform (LowerTrace) 52 4-4. ElectronicCircuitUsedtoShapetheAbsorption SignaloftheVaporCellintotheReferenceSignal 55 4-5. DifferentTypesofModulatedSignals 58 5-1. SchematicDiagramoftheApparatusUsed forDiodeLaserAtomicFluorescences 66 5-2. EnergyLevelDiagramShowingtheRubidium TransitionsUsedinThisStudy 69 6-1. SchematicsandTerminologyfortheThree ProposedExperimentalArrangements 78 6-2. GraphicalDepictionofDoffandD0n 85 6-3. DetailDrawingoftheExperimentalArrangement UsedtoStudyCaseA 88 6-4. DetailDrawingoftheExperimentalArrangement UsedtoStudyCaseC 90 6-5. WaterJacketUsedtoControlCellTemperature 95 6-6. RubidiumAbsorptioninaVaporCellat14.4°C 98 6-7. PlotofAbsorptionFactorVersusRubidium NumberDensity 100 6-8. OscilloscopeTraceShowingtheAbsorption oftheFlameSuperimposedontheAbsorption oftheVaporCell 104 viii A-l. ExperimentalArrangementUsedtoMeasure AbsorptioninanHollowCathodeLamp 112 A-2. ExperimentalLayouttoMeasureAtomic FluorescenceSimultaneouslyinthe HollowCathodeLampandFlame 114 A-3. RubidiumAbsorptionMeasuredina HollowCathodeLamp 117 A-4. RubidiumFluorescenceMeasuredina HollowCathodeLampandinaFlame 119 ix AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy DIODELASERATOMICSPECTROSCOPY By TyeEdBarber May1992 Chairperson: JamesD.Winefordner MajorDepartment: Chemistry A single mode semiconductor laser was used as the source for atomic absorptionandatomicfluorescence spectroscopy. Toovercometheproblemsof tuningthediodelasertothedesiredfrequencyandthefrequencyinstabilitiesor driftsofthelaseremissionfrequency,anewreferencingapproachwasused. The emission frequencyofthelaserwasmodulated acrosstherubidium transition at 780.023 nm, and the absorption or fluorescence signal was detected in an air hydrogenflame. Theatomicsignalsweremeasuredbyalock-inamplifier. The referencesignalforthelock-inamplifierwasgeneratedbytheatomicabsorptionof rubidium in an atomicvaporcell. As the laser frequency fluctuated, no phase changeoccurredbetweenthereferenceandanalyticalsignalssincetheywereboth generatedsimultaneouslybythesameatomictransition. Thiseliminatedanynoise orsignallossthatwouldhavebeencausedbyusingareferencemethodwhichdid x