Principles of Lasers

624 Pages·2010·6.901 MB·English

by  Orazio Svelto (auth.)

Principles of Lasers
FIFTHEDITION
Principles of Lasers
FIFTHEDITION
Orazio Svelto
PolytechnicInstituteofMilan
andNationalResearchCouncil
Milan,Italy
TranslatedfromItalianandeditedby
David C. Hanna
SouthamptonUniversity
Southampton,England
123
OrazioSvelto
PolitecnicodiMilano
Dipto.Fisica
PiazzaLeonardodaVinci,32
20133Milano
Italy
ISBN978-1-4419-1301-2 e-ISBN978-1-4419-1302-9
DOI10.1007/978-1-4419-1302-9
SpringerNewYorkDordrechtHeidelbergLondon
LibraryofCongressControlNumber:2009940423
1stedition:(cid:2)c PlenumPress,1976
2ndedition:(cid:2)c PlenumPublishingCorporation,1982
3rdedition:(cid:2)c PlenumPublishingCorporation,1989
4thedition:(cid:2)c PlenumPublishingCorporation,1998
(cid:2)c SpringerScience+BusinessMedia,LLC2010
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To my wife Rosanna
and to my sons Cesare and Giuseppe
Preface
Thisbookismotivatedbytheveryfavorablereceptiongiventothepreviouseditionsaswell
as bythe considerablerangeof new developmentsin the laser field since thepublicationof
thethirdeditionin1989.Thesenewdevelopmentsinclude,amongothers,Quantum-Welland
Multiple-QuantumWelllasers,diode-pumpedsolid-statelasers,newconceptsforbothstable
and unstable resonators, femtosecondlasers, ultra-high-brightnesslasers etc. The basic aim
ofthebookhasremainedthesame,namelytoprovideabroadandunifieddescriptionoflaser
behavioratthesimplestlevelwhichiscompatiblewithacorrectphysicalunderstanding.The
bookisthereforeintendedasatext-bookforasenior-levelorfirst-yeargraduatecourseand/or
asareferencebook.
Thiseditioncorrectsseveralerrorsintroducedinthepreviousedition.Themostrelevant
additionsorchangestosincethethirdeditioncanbesummarizedasfollows:
1. A much-more detailed description of Amplified Spontaneous Emission has been
given [Chapt. 2] and a novel simplified treatment of this phenomenon both for
homogeneousorinhomogeneouslineshasbeenintroduced[AppendixC].
2. A major fraction of a chapter [Chapt. 3] is dedicated to the interaction of radiation
withsemiconductormedia,eitherinabulkformorina quantum-confinedstructure
(quantum-well,quantum-wireandquantumdot).
3. Amoderntheoryofstableandunstableresonatorsisintroduced,whereamoreexten-
sive use is made of the ABCD matrix formalism and where the most recent topics
ofdynamicallystableresonatorsaswellasunstableresonators,withmirrorshaving
Gaussianorsuper-Gaussiantransversereflectivityprofiles,areconsidered[Chapt.5].
4. Diode-pumping of solid-state lasers, both in longitudinal and transverse pumping
configurations, are introduced in a unified way and a comparison is made with
correspondinglamp-pumpingconfigurations[Chapt.6].
5. Spatially-dependentrateequationsareintroducedforbothfour-levelandquasi-three-
levellasersandtheirimplications,forlongitudinalandtransversepumping,arealso
discussed[Chapt.7].
vii
viii Preface
6. Laser mode-locking is considered at much greater length to account for e.g. new
mode-locking methods, such as Kerr-lens mode-locking. The effects produced by
second-orderandthird-orderdispersionofthelasercavityandtheproblemofdisper-
sioncompensationtoachievetheshortestpulse-durationsarealsodiscussedatsome
length[Chapt.8].
7. New tunable solid-state lasers, such as Ti: sapphire and Cr: LISAF, as well as
new rare-earth lasers such as Yb3C, Er3C, and Ho3C are also considered in detail
[Chapt.9].
8. Semiconductor lasers and their performance are discussed at much greater length
[Chapt.9].
9. The divergence properties of a multimode laser beam as well as its propagation
through an optical system are considered in terms of the M2-factor and in terms of
theembeddedGaussianbeam[Chapt.11and12].
10. The production of ultra-high peak intensity laser beams by the technique of
chirped-pulse-amplificationandthe relatedtechniquesofpulse expansionandpulse
compressionarealsoconsideredindetail[Chapt.12].
The book also contains numerous, thoroughly developed, examples, as well as many
tablesandappendixes.Theexampleseitherrefertorealsituations, asfoundintheliterature
or encountered through my own laboratory experience, or describe a significative advance
in a particulartopic.Thetablesprovidedataonoptical, spectroscopicandnonlinear-optical
propertiesoflasermaterials,thedatabeingusefulfordevelopingamorequantitativecontext
aswellasforsolvingtheproblems.Theappendixesareintroducedtoconsidersomespecific
topicsinmoremathematicaldetail.Agreatdealofefforthasalsobeendevotedtothelogical
organizationofthebooksoastomakeitscontentmoreaccessible.
Thebasicphilosophyofthebookistoresort,whereverappropriate,toanintuitivepicture
rather than to a detailed mathematical description of the phenomena under consideration.
Simple mathematical descriptions, when useful for a better understanding of the physical
picture, are includedin the textwhile the discussion of more elaborateanalyticalmodelsis
deferredtotheappendixes.Thebasicorganizationstartsfromtheobservationthatalasercan
beconsideredtoconsistsofthreeelements,namelytheactivemedium,theresonator,andthe
pumpingsystem.Accordingly,afteranintroductorychapter,Chapters2–3,4–5and6describe
themostrelevantfeaturesoftheseelements,separately.Withthecombinedknowledgeabout
these constituentelements, chapters7 and 8 then allow a discussion of continuos-waveand
transientlaserbehavior,respectively.Chapters9and10thendescribethemostrelevanttypes
oflaserexploitinghigh-densityandlow-densitymedia,respectively.Lastly,chapters11and
12 consider a laser beam fromthe user’s view-pointexaminingthe propertiesof the output
beamaswellassomerelevantlaserbeamtransformations,suchasamplification,frequency
conversion,pulseexpansionorcompression.
Withsomanytopics,examples,tablesandappendixes,itisclearthattheentirecontent
of the book could not be covered in only a one semester-course. However the organization
ofthebookallowsseveraldifferentlearningpaths.Forinstance,onemaybemoreinterested
inlearningthePrinciplesofLaserPhysics.Theemphasisofthestudyshouldthenbemostly
concentratedonthefirstsectionofthebook[Chapt.1–5andChapt.7–8].If,ontheotherhand,
thereaderismoreinterestedinthePrinciplesofLaserEngineering,effortshouldmostlybe
concentrated on the second part of the book Chap. 6 and 9–12. The level of understanding
Preface ix
of a given topic may also be suitably modulated by e.g. considering, in more or less detail,
the numerousexamples, which often representan extensionof a giventopic, as well as the
numerousappendixes.
Writingabook,albeitasatisfyingculturalexperience,representsaheavyintellectualand
physicaleffort.This efforthas, however, been gladly sustained in the hope that this edition
canservethepressingneedforageneralintroductorycoursetothelaserfield.
ACKNOWLEDGMENTS. I wish to acknowledge the following friends and colleagues,
whose suggestionsand encouragementhave certainly contributedto improvingthe book in
anumberofways:ChristoferBarty,VittorioDeGiorgio,EmilioGatti,DennisHall,Gu¨nther
Huber, Gerard Mourou, Colin Webb, Herbert Welling. I wish also to warmly acknowl-
edge the critical editing of David C. Hanna, who has acted as much more than simply a
translator. Lastly I wish to thank, for their useful comments and for their critical reading
of the manuscript, my former students: G. Cerullo, S. Longhi, M. Marangoni, M. Nisoli,
R.Osellame,S.Stagira,C.Svelto,S.Taccheo,andM.Zavelani.
Milano OrazioSvelto
Contents
ListofExamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
1. IntroductoryConcepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1. SpontaneousandStimulatedEmission,Absorption . . . . . . . . . . . . . . . . . . 1
1.2. TheLaserIdea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. PumpingSchemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. PropertiesofLaserBeams . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4.1. Monochromaticity . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4.2. Coherence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4.3. Directionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.4. Brightness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4.5. ShortTimeDuration . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.5. TypesofLasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.6. OrganizationoftheBook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2. InteractionofRadiationwithAtomsandIons . . . . . . . . . . . . . . . . . . 17
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2. SummaryofBlackbodyRadiationTheory . . . . . . . . . . . . . . . . . . . . . 17
2.2.1. ModesofaRectangularCavity . . . . . . . . . . . . . . . . . . . . . . 19
2.2.2. TheRayleigh-JeansandPlanckRadiationFormula . . . . . . . . . . . . . . 22
2.2.3. Planck’sHypothesisandFieldQuantization . . . . . . . . . . . . . . . . . 24
2.3. SpontaneousEmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.1. SemiclassicalApproach . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.2. QuantumElectrodynamicsApproach . . . . . . . . . . . . . . . . . . . . 30
2.3.3. AllowedandForbiddenTransitions . . . . . . . . . . . . . . . . . . . . . 31
xi
xii Contents
2.4. AbsorptionandStimulatedEmission . . . . . . . . . . . . . . . . . . . . . . . 32
2.4.1. RatesofAbsorptionandStimulatedEmission . . . . . . . . . . . . . . . . 32
2.4.2. AllowedandForbiddenTransitions . . . . . . . . . . . . . . . . . . . . . 36
2.4.3. TransitionCrossSection,AbsorptionandGainCoefficient . . . . . . . . . . . 37
2.4.4. EinsteinThermodynamicTreatment . . . . . . . . . . . . . . . . . . . . 41
2.5. LineBroadeningMechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.5.1. HomogeneousBroadening . . . . . . . . . . . . . . . . . . . . . . . . 43
2.5.2. InhomogeneousBroadening . . . . . . . . . . . . . . . . . . . . . . . 47
2.5.3. ConcludingRemarks . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.6. NonradiativeDecayandEnergyTransfer . . . . . . . . . . . . . . . . . . . . . . 50
2.6.1. MechanismsofNonradiativeDecay . . . . . . . . . . . . . . . . . . . . 50
2.6.2. CombinedEffectsofRadiativeandNonradiativeProcesses . . . . . . . . . . . 56
2.7. DegenerateorStronglyCoupledLevels . . . . . . . . . . . . . . . . . . . . . . 58
2.7.1. DegenerateLevels . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.7.2. StronglyCoupledLevels . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.8. Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.8.1. SaturationofAbsorption:HomogeneousLine . . . . . . . . . . . . . . . . 64
2.8.2. GainSaturation:HomogeneousLine . . . . . . . . . . . . . . . . . . . . 67
2.8.3. InhomogeneouslyBroadenedLine . . . . . . . . . . . . . . . . . . . . . 69
2.9. DecayofanOpticallyDenseMedium . . . . . . . . . . . . . . . . . . . . . . . 70
2.9.1. RadiationTrapping . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.9.2. AmplifiedSpontaneousEmission . . . . . . . . . . . . . . . . . . . . . 71
2.10. ConcludingRemarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3. EnergyLevels,RadiativeandNonradiativeTransitionsinMolecules
andSemiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.1. Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.1.1. EnergyLevels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.1.2. LevelOccupationatThermalEquilibrium . . . . . . . . . . . . . . . . . . 85
3.1.3. StimulatedTransitions . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.1.4. RadiativeandNonradiativeDecay . . . . . . . . . . . . . . . . . . . . . 91
3.2. BulkSemiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.2.1. ElectronicStates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.2.2. DensityofStates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3.2.3. LevelOccupationatThermalEquilibrium . . . . . . . . . . . . . . . . . . 98
3.2.4. StimulatedTransitions . . . . . . . . . . . . . . . . . . . . . . . . . . 101
3.2.5. AbsorptionandGainCoefficients . . . . . . . . . . . . . . . . . . . . . 104
3.2.6. SpontaneousEmissionandNonradiativeDecay . . . . . . . . . . . . . . . . 110
3.2.7. ConcludingRemarks . . . . . . . . . . . . . . . . . . . . . . . . . . 112
3.3. SemiconductorQuantumWells . . . . . . . . . . . . . . . . . . . . . . . . . 113
3.3.1. ElectronicStates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
3.3.2. DensityofStates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Contents xiii
3.3.3. LevelOccupationatThermalEquilibrium . . . . . . . . . . . . . . . . . . 118
3.3.4. StimulatedTransitions . . . . . . . . . . . . . . . . . . . . . . . . . . 119
3.3.5. AbsorptionandGainCoefficients . . . . . . . . . . . . . . . . . . . . . 121
3.3.6. StrainedQuantumWells . . . . . . . . . . . . . . . . . . . . . . . . . 125
3.4. QuantumWiresandQuantumDots . . . . . . . . . . . . . . . . . . . . . . . . 126
3.5. ConcludingRemarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
4. RayandWavePropagationThroughOpticalMedia . . . . . . . . . . . . . . . 131
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
4.2. MatrixFormulationofGeometricalOptics . . . . . . . . . . . . . . . . . . . . . 131
4.3. WaveReflectionandTransmissionataDielectricInterface . . . . . . . . . . . . . . . 137
4.4. MultilayerDielectricCoatings . . . . . . . . . . . . . . . . . . . . . . . . . . 139
4.5. TheFabry-PerotInterferometer . . . . . . . . . . . . . . . . . . . . . . . . . 142
4.5.1. PropertiesofaFabry-PerotInterferometer . . . . . . . . . . . . . . . . . . 142
4.5.2. TheFabry-PerotInterferometerasaSpectrometer . . . . . . . . . . . . . . . 146
4.6. DiffractionOpticsintheParaxialApproximation . . . . . . . . . . . . . . . . . . 147
4.7. GaussianBeams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
4.7.1. Lowest-OrderMode. . . . . . . . . . . . . . . . . . . . . . . . . . . 150
4.7.2. FreeSpacePropagation . . . . . . . . . . . . . . . . . . . . . . . . . 153
4.7.3. GaussianBeamsandtheABCDLaw . . . . . . . . . . . . . . . . . . . . 156
4.7.4. Higher-OrderModes . . . . . . . . . . . . . . . . . . . . . . . . . . 158
4.8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
5. PassiveOpticalResonators . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
5.2. EigenmodesandEigenvalues . . . . . . . . . . . . . . . . . . . . . . . . . . 167
5.3. PhotonLifetimeandCavityQ . . . . . . . . . . . . . . . . . . . . . . . . . . 169
5.4. StabilityCondition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
5.5. StableResonators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
5.5.1. ResonatorswithInfiniteAperture . . . . . . . . . . . . . . . . . . . . . 175
5.5.1.1. Eigenmodes . . . . . . . . . . . . . . . . . . . . . . . . . 176
5.5.1.2. Eigenvalues . . . . . . . . . . . . . . . . . . . . . . . . . . 180
5.5.1.3. Standing-andTraveling-WavesinaTwo-MirrorResonator . . . . . . . 182
5.5.2. EffectsofaFiniteAperture . . . . . . . . . . . . . . . . . . . . . . . . 183
5.5.3. DynamicallyandMechanicallyStableResonators . . . . . . . . . . . . . . . 186
5.6. UnstableResonators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
5.6.1. Geometrical-OpticsDescription . . . . . . . . . . . . . . . . . . . . . . 190
5.6.2. Wave-OpticsDescription . . . . . . . . . . . . . . . . . . . . . . . . . 192