Diode laser atomic spectroscopy

138 Pages·1992·3.9 MB·English

by  Barber, Tye Ed

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