LASER FUNDAMENTALS
`
`SECOND EDITION
`
`WILLIAM T. SILFVAST
`
`School 01 Optics ICRECIL
`University of Central Florida
`
`;-'i':_I CAMBRIDGE
`
`UNIVERSITY PRESS
`
`i
`
`ASML 1106
`ASML 1106
`
`

`
`PUBLISHED BY THE PRESS SYN DKLATE OF THE UNIVERSITY DF CAMBRIDGE
`The PM Building. TmmpingIuI1Slmet.Cai'uhridgi:. United Kingdom
`
`EhflEIEil!Dl_'rE UNIVERSITY PRESS
`The Eclinhurgh Building, Cambridge EE2 ZRU. UK
`-IJJWEE1 E Street. Netwfidrk. N1’ 11101]--1-Zll. 115.9;
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`Duck Hausa, TIE WaleIfi1:II3t.Chpe'I‘|:IwI1 BED]. Smlhfiflica
`hItp:Fiwww.c:amhridge.ou'g
`
`First published 1996
`RE1'.|I'I2|'lIJBfl I999. ‘I000. EIIIG
`
`First edition® University Press
`Second sdidusl BI Wfliiam T. Silfnst 25104
`
`This boat is 'LI1c,a1:]I'r'|3hl_ Subject In staiulnry an:e1:|Li-EII3 and
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`norapu'Dduc1inI1uI'a.rI3r part may I512 place w1'IIimul
`the IArI'iiIerI paamissim dfcamhlidge Unhnezsily Press.
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`First puhlisbaadlfllld
`
`Printed in line United Slams dEA.:I1.eriI::n
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`Typrgfaca 'E'i|1:n=_-s1E|I_5i'i|15 and Auanir
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`A. raining rzmriijbr this boat Lrmuiiabiefmm rhrflririfli i'..r'u5rr.I'r_v_
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`i'..:'i!J.rr:n'j.I of Com311233 Caraioging in Pubiicariotr atda
`5-I.I.f1-ESL 'W'Ii|:ia|:n 'I'h.mI'Las.1*3|3T—
`Lmer E:.Lr|d.arue1IaIsi"i|'iIli:a.In T. Siifvasl. — Ended.
`:1.
`cm.
`includes bihfiogajyllic-ai refozmme-5 and indacu.
`ISBN 0-521-53345-0
`I. Lasers.
`I. 1153.
`
`TAI6-'J‘5.S52 E04
`I52l_3IS’1S — d::"Z]
`
`ISBN fill 833-I5 III hardback.
`
`EEIUBCISSJSE
`
`ii
`ll
`
`

`
`page xix
`1|'.J(i
`
`uiii
`
`LII-I'i-Ln‘It\JhJ————
`
`Contents
`
`Preface to the Second Edirion
`
`Prefiice to the Firm‘ Edition
`
`.-tcicnowtedgments
`
`1
`
`INTRDIJUCTION
`D'II'E.II‘.\I"IE'H'
`intm-ductiou
`Definilitirl of the Laser
`
`SirnpI.iI:'ity til’ a Laser
`Unique Properties of :1 Laser
`The Laser Speclrum and 'Iv'\-'aI.'eln3*nglIIs
`A Brief History‘ tithe Laser
`(lweniew of the Iluoii.
`
`SECTION 1. FUNDAMENTAL WAVE PROPEIITJES OF 1.IGi-IT
`
`2 WAVE NATURE OF LIGHT — THE INTERACTION CIF LIGHT
`WITI-i i'i'IJltTERIIlu.|I.5
`D-'Ir'EIHI']E'|'t'
`
`2.] Maimi-ll’s Equations
`2.1 .‘vIaim'ell’5 ‘n-Ir':.«m.- Equations
`Max-weII’5 Wave Equations for a Vacuuni
`Solution of the General Wave Equation — Equivalence of Light and
`Eioctromagneuc Radiation
`Wave ‘|n’eiocit_I;' — Phase and Group Veiocities
`Gflt'.DEl':]I2I2'.ECI Solution of LI'Le Wave Equation
`Transverse Eloctromagnefic Waves and Poiarixed Light
`Flow of Electromagnetic Energy
`Radiation from a Point Source (Electric Dipole Radialioni
`2.3 Interaction of Eleolmmagnetit RadiaIioI1{LiglIlt with hlalter
`Speed of Light in a Metlium
`Maxwell’: Equations in :1 Medium
`Application of Ma.xwol!'s Eq1.1ation.s to Dielectric Materials —
`Laser Gain Media
`
`Complex Index of Refraction — Optical Constants
`Absorption and Dispersion
`
`

`
`viii
`
`CONTENTS
`
`34
`36
`37
`
`39
`
`45
`45
`45
`45
`
`49
`5 I
`54
`54
`54
`515
`515
`ST
`57
`59
`
`I53
`
`67"
`67
`63
`69
`
`'30
`72
`'32
`
`Estimating Particle Densities of Materials for Use in the
`Dispersion Equations
`1.-I Co-]terertr:e
`
`Temporal Coherence
`Spalisl Coherence
`REFERENCES
`PRDIILECIAIS
`
`SECTION 2. F1Jl'IlD.t'tMENTAL Gl.I.lHTlJM PRBPERTIES OF LIGHT
`
`3 PARTICLE NATURE OF LIGHT — DISCRETE ENERGY LEVELS
`D"t'FJl'l-'lE'W
`
`J-.1 Bohr Theory of the Hydrogen Atom
`Historical Development of the Concept oi Discrete Energy Levels
`Energy Levels of the Hydrogen Atom
`Frequency and Wavelength of Emission Lines
`Ionization Energies a.nd Energy Levels oflons
`Photons
`
`3-.2 Quantum Theory of Atomic Ettergy Iitw-els
`Wat-‘e Nature of Particles
`
`Heisenberg Urtcusrtalnty Principle
`Wave Theory
`Wave FEEHCIIUFB
`Quantum States
`'l11e Schrfidingerwave Equation
`Energy and Wave Function for the Ground State of the
`Hydrogen Atom
`Excited States of Hydrogen
`Allowed Quantum Numbers for Hydrogen Atom Wave Functions
`3.3 Anguhr Momfiilum of Alorrts
`Orbital Angttlsr Momentum
`Spin Angular Momentum
`Total Angular ]'Ulon'Lenta.1m
`3.4 Fatergy l..e\-xels Associated with Clllll.‘-I‘:Ii!¢.‘l2l'|E'lI] Atoms
`fine Structure of Spectral Lines
`Pauli Exclusion Principle
`J-.5 Periodic Table u-Mlle Elernents
`
`Quantum Conditions Associated with Muluple Electrons Attached
`to Nuclei
`
`Shorthand Notation for Electronic Configurations of Atoms Having
`More Than One Electron
`
`3-.6 F.Iterg_I.' Lew.-Isol‘ |.'tIulti-FJe1.'tron .-atoms
`Energy—l..e~.re1 D-esignatiort for Mul1i—ElecI.ron States
`Rus.sell—Sa.unde.rs or L3 Coupling — Notation for Energy Levels
`Energy ]_r.";vels Associated with Two Electrons in Unfilled Shells
`Rules for Obtaining S. L. and J for [.3 Coupling
`Degeneracy and Stausdral Weights
`Coupling
`Isoelectronic Scaling
`
`

`
`CONTENTS
`
`REFERENCES
`FRGBLEE1-‘IS
`
`4 R.ADl.:I.T|‘."£ TRANSITIDNS ANI} EMISSION LINEWIDTH
`OVERVIEW
`
`Ilecay o:I'Excited States
`4.]
`Radiative Decay of Excited States of Isolated Atoms —
`Spoinaneoats Emission
`Spontaneous Emission Decay Raic — Radiative Transition
`Probability
`Lifetime of a Radiating Eiectron — Tl1e Electron as a Classical
`Radiating Harmonic Oscillator
`Nonradiative Decay of die Excited States — Collisional Decay‘
`-L1 Emission Bniraniesiing and [Jnewidth Due to Radiative Decay
`Classical Emission Linewiclrll of a Radiating Electron
`Natural Emission Linewitlth as Dccluced by Quantum Mechanics
`I[Minin1urr| Linewidtit}
`4.3 Additional F.n:':s'sio£I-Ii-roadening Processes
`Broadening Due to Nonradiatiue {l'_'oITisionaIl Decay
`Broadening Due to Dephasing Collisions
`.n.n1orphous Crystal Broadening
`Doppler Broslzlening in Gases
`‘rhigt Lineshape Profile
`Broadening in Gases Due to Isotope Sliifls
`Cornpari son of l-"arious Types of Emission Broadening
`-I.-II Quanlum Meclianicul DB".5C'.l'lpl.l.fl-fl of Rarliating A1-:u'ns
`Electric Dipole Radiation
`Electric Dipole Mani; Element
`Electric Dipole Transition Probability
`Oscillator Strength
`Selection Rules for Electric Dipole Transitions Involving Atoms
`'W'lli'l a Single Electron in an Unfillerl SHIIISLIBII
`Selection Rules for R:I:lia::i1.'e Transitions lmroli.-ing fiuorns with
`More Than One Electron in an Unlillccl Subdtell
`
`Parity Selection Rule
`lncfficient Radiative Transitions — Electric Quadrupole and Gdier
`Higlier-Onrler Transitions
`REFERENCES
`FRDBLEMS
`
`5 ENERGY LEVE LS AND RADIATNE PROPERTIES OF MOLECULES.
`LIQUIDS. AND SOLIDS
`D'l:'E.ll‘lI'lE'llI'
`
`5.1 Molecular Energy Levels a.n.d Spectra
`Energy Levels of Molecules
`Classification of Simple Molecules
`Rotational Energy Levels of Linear Molecules
`Rotational Energy: Levels of S3'mrne*o'ic—Top Molecules
`Selection Rules for Rotational Transiuons
`
`39
`89
`
`94
`
`'95
`
`ill]
`I01
`
`I03
`I05
`I06
`I0"?
`I09
`l|I.'F9
`H4
`H5
`llli
`I2]
`I22
`l23
`ll-'-I
`l24
`
`lfifi
`
`l29
`l3l.'l
`
`l3|
`l3l
`ii-ll
`
`H5
`135
`H5
`H5
`133
`H9
`14-]
`i4]
`
`

`
`CIDHTEHTS
`
`"u’iIJrationaJ Energy Levels
`Selection Rule for Vibratiolsal Transitions
`Rotat.ional—‘l"i|:raLional Transitions
`Prolziala-i]:ities of Rotational III Vibrational Trarisilions
`
`Electronic Energy Levels of Molecules
`Electronic Transitions and Associated Selection Rules of
`Molecules
`En'Lission Linewidth of Molecular Transiuons
`
`The Franclt—Condon Principle
`Escimer Energy Levels
`5.2 Liquid F.;aerg}' I..r."ri.-B and Their Radiafion Properties
`Structure oI'D}'e Molecules
`Energy Levels of Dye Molmules
`Excitation and Emission of Dye Molecules
`Deuamental Triplet States ofD}.re Molecules
`5.3 F.neI'g}' Levels in Solids — Dielectric I.ase:r lrlalerials
`l-lost lilatedsls
`
`Laser Species — Dopant lens
`l"la.rrov.'-LinewidtJ1 Laser In-lsterials
`Broadband Tunable Laser It-laterials
`
`Broadening Mechanism for Solid-Slate Lasers
`5.1- F.11cI'g_v Levels in Solids — Semiconductor Laser Ildateriak
`Energy Bands in Ctjpstallinc Solids
`Energy Levels in Periodic Structures
`Energy Levels ol'Conducto1:s. Insulators. and Semiconductors
`Excitation and Decay of Excited Ealergy Levels — Recombination
`Radiation
`
`Direct and indirect Eandgap Secnnaconrloctors
`Electron Distribution Function and Density of States in
`Serrliconductors
`lrnri nsic Semiconsrluctor Maerials
`
`Extrinsic Semiconductor Materials — Doping
`|:I—n Junctions — Recombination Radiation Due to Electrical
`Eatcitati on
`
`l-lcterojuuction S-crniconductor Materials
`E_Iuam1.uT: Wells
`"I-’ariao'on of flandgap Energy and Radiation ‘Wavelength with
`Alloy Composition
`Recombination Radiation Transition PfiDlJ9l!|ilil'}' and Linewidth
`nessnewces
`snosmms
`
`5 RADIATION Mtilll THERMAL EQUILIBRIUM — ABSORPTION AND
`STIMULATED EMISSION
`ovniwlaw
`
`15.1 Equililirittna
`Tl'ie.rn'Jal Equilibrium
`Tl'iern'ial Equilibrium via Conduction and Connection
`Tlaernaal Equilibrium via Radiation
`
`143
`143
`144
`143
`
`149
`
`150
`150
`
`l5l
`152
`153
`J53-
`153
`15-S
`IS?
`153
`153
`
`159
`lfi-l
`I66
`
`163
`J65
`[I53
`ITO
`1T2
`
`11'3-
`
`1T4
`
`ITS
`1T9
`
`IT‘?
`
`J82
`
`J34
`IE6
`
`l9l
`195
`195
`195
`
`199
`199
`
`199
`199
`ZEN]
`Ell]
`
`

`
`2D|
`20-4
`205
`206
`20''?
`203
`
`E 2
`
`10
`
`21I
`214
`215
`Elli
`217'
`El
`El
`
`225
`225
`225
`
`229
`
`230
`
`23 I
`232
`
`233
`234
`235
`233
`
`233
`24 I
`244
`245
`247
`24'?
`243
`249
`253
`253
`
`CONTENTS
`
`6.1 Radiating Bodies
`Ste*fan—Bo1tzmann Law
`Wien‘s I..av.'
`Irratzliance and Radianoe
`
`6.3- Cavity Radiation
`Cou oling the Nurnbet of Cavity Modes
`Ra}rleigh—.I£-ans Formula
`Planck‘: Law for Cavity Radiation
`Relationship between Cavity Radiation and Blaokbody
`Radiation
`
`Wavelength Dependence of Blaekbodv Emission
`6.4 Alisorpiioli and Stimulated Elllifilflfl
`The Principle of Detailed Balanoe
`Absorption and Stimulated Emission Coeificients
`REFERENCES
`I'E~I}IlLE!o'IS
`
`SECTION 3. LASER AMPLIFIERS
`
`3' EON DITICIN5 FOR PRODUCING A LASER — PDPU LATIIBN
`INVERSIDN5. GAIN. AND GAIN SATURATION
`D"l:"E.'IIJtI'IE‘Ii'l'
`
`7.1 Ahsorptiqm and Cain
`Alivsotption and Gain on a Homogeneously Btoadened Radiative
`Transition [Lorentzian Frequency’ Distribution}
`Gain Coeliieient and Sli II|.1iiaIl:'!-CI Emission Cross Section for
`
`Homogeneous Broadening
`Absorption and Gain on an lnhomogerteously Broadened Radiative
`Transition [Doppler Broadening wit]: a Gaussian Disttibuli cIn'I
`Gain Coefiieient and Eli mulated Emission Cross Setaion for
`
`Do-pplet Broadening
`Statistiusai Weights and Ihr: Gain Equation
`Relationship of Gain CoeFficie:nt and Sti mutated Emission
`Cross Section to Absorption Coeffieient and Absorption
`Cross Section
`
`T.'." Population inversion tI"ie<:essar3' Condition for :1 I.as-err
`T.3- S.1iu:r'.1I.ion Intensity tSuI'Iit.'ienl Condition for a Laser]
`T.4 Development and Growth of a Laser Beam
`Growth ot'Besm for a Gain Mediunt with Homogeneous
`Broadening
`Shape or Geometry of Amplifying Medium
`Growth of Bea.m for Doppler Broadening
`T.5 Exptmesitial Crovrtil Factor {Cain}
`]".I3i
`'l'|n'eshoIIl Require:-nents for a Laser
`Laser with No lviirrors
`Laser with Gne Mirror
`Laser with Two Milvors
`REFERENCES
`FIGILENIS
`
`

`
`xii
`
`CONTENTS
`
`LALSER OSCILLATIDH ABOVE THRESHOLD
`DVERVIEW
`3.1 Laser Gain Saturation
`
`Rate Equations of the Laser Levels That Include Stimulated
`Erni5sio:rt
`
`Population Densities of Upper and Lower Laser Levels with
`Beam Present
`
`Email-Signal Gain Coeffioient
`Saturation of the Laser Gain aboi-we Threshold
`
`3.2 Laser Beam Growth be}-orid the Saluralion I]1fl£‘l'ISil'_|.'
`Change from Eitponentiai Grormh to Linear Growth
`Steady-S tare Laser intensity
`3.] flptiinization ol'l.as>er Clutpol Power
`-Dptimum Output Minor Transmission
`Optimum Laser Dutput Intensity
`Estimating Optimum Laser Dutput Power
`8.4 Fmergy Exchange between Upper Laser Level Population and
`Laser Photons
`Decay Time ofa Laser Beam wi'|hin an Optical Cavity
`Basie Laser Cavity Rate Equauons
`Steady-S Late Solutions below Laser Threshold
`Steady-S taLe Elperalion ali-owe Laser Threshold
`3.5 Laser Dutptut l.*'luetua1ions
`Laser Spflcing
`Relaxation Elseiilations
`
`8.6 Laser Anlplijiers
`Basie Amplifier Uses
`Propagation of a High-Power. Short-Duration I.'.'|'pI.ieal Pulse through
`an Amplifier
`Salzuration Energy Fluenee
`Atnrplifying Long Laser Pulses
`.A.mpI.iI'}'i ng Short Laser Pulses
`Comparison of Efficient Laser Amplifiers Based upon Fundamental
`Sat1.IraIio-rt Lcimits
`
`it-'iin'or Array and Resonator '[RE'E£.‘I1El'2l.i‘U£.‘.) Amplifiers
`REFERENCE
`P‘Jll'.'|IIlLEMS
`
`REQUIREMENTS FOR OBTAINING PCIPULATIDN INVERSIDN5
`DVERVIEW
`
`9.1 [:11-'ers'Ions and Two-l.e1.'eI S_-rstems
`9.2 Relative Decay Rates — Hatliatzive 1-'ersos Collisions]
`9.3 Stead}-Slate Inversion: in TII:n=.-e- and Four-Level Systeius
`']1'i.ree-L.e\'el Laser with die Irttennedinte Level as the Upper Laser
`Level
`
`TI'Lree-L.e1.'ol Laser with the Upper Laser Level as Ihe Highest Level
`Four—Lei-'eI Laser
`
`9.4 Transient Population ln1-'ersio11s
`
`255
`255
`255
`
`256
`252
`252
`253
`253
`2.6!
`2151
`2151
`215-4
`2154
`
`2615
`262
`263
`220
`222
`223
`223
`2215
`229
`229
`
`230
`282
`234
`234
`
`235
`285
`283
`283
`
`290
`290
`290
`292
`293
`
`295
`293
`3!]!
`304
`
`

`
`CEITIENTS
`
`9.5 Processes Thal lnlliliil or Destmy Inversinns
`Raxiiati on Trapping in Atorns and Ions
`Electron Collisio-nal Tlnertnalization of the Laser Levels in Atoms
`and Ions
`
`Comparison oi Radiation Trapping and Eleetroan Collision:-ll Mixing
`in a Gas Laser
`
`.€|.bsorpIi on williin the Gain Medium
`IIEIIEEENCES
`PIIGI-{EMS
`
`1D LASER PUIHIPIHG REQUIREMENTS AND TECHNIQUES
`OVERVIEW"
`
`1ll.1 Iixeilnfion or Punapiltg Threshold Ilequiremelits
`10.1 Pumping Pathways
`Excitation by Direct Pumping
`Excitation by Indirect Pumping {Pump and Transfer:
`Specific Pump-and-Tra.n5Ier Processes
`1ll.J- Specific Excitation Pfil'fiI'lIE‘1£E'l‘S fitssocialed with
`Optical Pumping
`Punnping Geometries
`Pumping Requirements
`A Simplified Optical Pumping Approximation
`Transverse Pumping
`End Pumping
`Diode Pumping of Solid—SIate Lasers
`Characterization ofa Laser Gain Medium with Opli cal Pumping
`(Slope Eflieiency]
`1|}.-1 Specific Excitalion Parameters Associalenl with
`Particle Pumping
`Electron Coilisionnl Pumping
`Heavy Particle Pumping
`A More Accurate Description of Electron Excitation Rule to a
`Specific Energy Level in a Gas Discharge
`Electrical Pumping of Semiconductors
`REFERENCES
`PRGIILEMS
`
`SECTION -d. 1.ASE|'\‘.RE5G‘H.IltTCI'ES
`
`11 LASER CAVITY MODES
`0\'E.1t\-‘IEW
`11.1 [l'IlII‘DI2Ill1.'i.'lEI|l'l
`
`11.1 Longillauiin.-al Laser Ca1ri.1'_I.' Modes
`Fn'|::r_',.-—Perol Resonator
`Fabr_',.-—Perol 1:3".-'l|I}' Modes
`Longitudinal Laser Cavity Modes
`Lon,-gintdinal Mode Number
`Req-uiremenls for the Development of Longiludi nal
`Laser Modes
`
`3-fl"II'
`
`3-1]
`
`3-15
`316
`3-19
`319
`322
`3-22
`322
`32-1
`3-24
`32'?
`3-30
`
`339
`339
`
`352
`
`3-55
`355
`3-59
`
`359
`36]
`3-63
`
`3'F|
`3?]
`3?]
`332
`3'?1'.
`3??
`33!}
`381]
`
`382
`
`

`
`xiv
`
`CONTENTS
`
`11.3 Transverse Laser Cavity Modes
`FresneI—K_irchhoF|' Diffraction Integral Forrn Lila
`Development of Transverse Modes in a Cavity witlt Plane-Parallel
`Mirrors
`
`12
`
`Transi.-'e.rse Modes Using Curved Mirrors
`Transverse Mode Spatial Disuibo Lions
`Transverse Mode Frequencies
`Gaussian-Sliaped Transverse Modes v.'itl'Lin and beyond the
`Laser Cavity
`1l.-1- Properties of Laser Modes
`Mode Characteristics
`Effect of Modes on the Gain Medium Profile
`REFERENCES
`FRDRLIMS
`STABLE LASER RESONATORS AND GAUSSIAN BEAMS
`D-\‘Ell'(']E'|'n'
`11.1 Stable Cu:n'ed Mirror Cavities
`Cun-wed Minor Cavities
`ABCD Mamces
`
`Cavity Stability Criteria
`12.2 Properties of Gaussian Be-ama
`Propagation ofa Gaussian Beam
`Gaussian Beam Properties GfTWD—MlHN Laser ‘Cavities
`Properties of Specific Two-Mirror Laser Cavities
`Mode Volume ofa Hermile—Gaussian Mode
`
`12.3 Properties of Real Laser E«ea.nJs
`J1.-1 Pmpagjatioa o:[ Gaussian Beams l_.'-sing ARCH Matrices —
`Complex Beam Parameter
`Cornpler. Beam Parameter Applied to a Two—?l-iirror Laser Cavity
`REFERENCES
`PROBLEMS
`
`13
`
`SPECIAL LASER EAI'n"lTlES AND CA‘|:I"lT‘l' EFFECTS
`DVERVIEW
`1.1.1 Unstable Resonators
`
`13.1 Q-Switching
`General Description
`Theory
`Methods of Producing Q-Switching within a Laser Cavity
`13.3 Gain-Suitchhg
`13.-I Mo-de-I..oc-king
`General
`Theory
`Techniques for Producing Mode-Locking
`13-.5 Pulse Shortening Techniques
`Self-Phase Modulation
`
`Pulse Sliorterting or Lengthening Using Group Velocity Dispersion
`Pulse Compression I|'S1:Lor-tening} with Gratings or Prisms
`Llltrashort-Pulse Laser and Amplifer System
`
`334
`335
`
`336
`39!]
`3'91
`3'92
`
`393
`3'96
`396
`39’?
`399
`399
`1'-1-[I2
`4-DE
`4-[I2
`4112
`
`4-11]
`411
`4-12
`41?
`421
`42 3
`
`425
`-123
`43 2
`4-3 2
`434
`434
`4-34
`439
`4-39
`44 I
`
`45!]
`4'-1-5 1
`45 1
`451
`456
`4-62
`4-63-
`
`46?
`
`

`
`CIDNTEIITS
`
`IV
`
`LLIS Ring Lasers
`Monolidlic Unidireclional Single-Mode Nd:‘I'AG Ring Laser
`TWO-Miflflf Ring Laser
`I3~.7 Complex Beam Parameter .JLI:|aI'_5'si'.s Applied Lo Multi-Jrlirror
`Laser Cafilies
`
`Three-Minor Ring Laser Cavity
`Threc— or Fa-Lrr—Mirro1' Focused Cavity
`llfl Cavities for I"mtIuI:1'11g Spectral Nanuwing of
`Laser flutpul
`Cavity with Additional Fabr}r—Pe1'ot Etalon for Narrow-Frequency
`S-cleaclion
`
`Tunable Cavity
`Broadband Tunable cw Ring Lasers
`Tunable Cavity’ for Ui1l'E.EI:].l'I'Dl'o'—FIi3qL|iBDL"_'f Output
`Disnibuted Feedback I{DFB‘] Lasers
`Diauibulod Bragg Reflection Lasers
`13.9 ]_.aaer C:u'ilie-3 Requiring S-m:|.iI-Diameter Cain Regions —
`.'-'tsl'ign1atiI.'aIl'_5' Compensated Catities
`I3_ll'I Waveguide families for Cal: [.‘J.El!'l§
`IIEFERENCES
`PROBLEMS
`
`SEETICIN 5. EPECJFI-E LASER SYETEMS
`
`1-II. LASER SYSTEMS INVOLVING LOW-[lEN'5lTY GAIN MEDIA.
`{W ER"r'IEW
`till Atonlit: Gas Lasem
`|.rLtroduI:iion
`Hel'ium—Ne-on ].:i:9er
`
`General Descriplion
`Laser S1:n1c1LiI'e
`Excitation Mechanism
`
`Application:
`.-trgola Ion I.aser
`General Descri plicrrt
`Laser S1:n.n:tL:re
`Excitation Mechanism
`
`Krypton Ion Laser
`Applications
`Heliu.m—CanirniI.Irn Laser
`
`General Descri plion
`Laser Strti-:I.uI'e
`Excitation Mechanism
`
`Applications
`Copper ‘Vapor 1.-aster
`Genera] Descriplion
`Laser Stnaelure
`Excitation Mechanism
`
`Applications
`
`453
`459
`4?!)
`
`4'."[I
`4?!)
`H3
`
`4?E
`
`438
`MS
`48!]
`48%]
`48|
`434
`
`484
`485
`486
`488
`
`4E'|I
`49I
`49I
`49I
`492
`492
`493
`4'34
`4'3?
`49?
`49?
`498
`499
`_'i{JG
`jrfll
`SDI
`SCIII
`502
`304
`505
`
`505
`5-E|".I‘
`:iE|'".I‘
`
`

`
`CONTENTS
`
`‘I-1.2 Itioieullar Gas Lasers
`Introduction
`Carl:-on Dinxitlc Laser
`
`Genera} Description
`Laser Smicmrc
`Excitation Mechanism
`
`Applications
`EIITIIDET Lasers
`
`General Description
`Laser Slnicture
`Excitation Mechanism
`
`.A.ppIicaI.ion.s
`Nitrugim [am
`Genera} Description
`Laser Structure and Excilaiion Mechanism
`
`Applications
`Far-1n.|'ratned Gas Lasers
`
`Geiicrai Description
`Laser Structure
`E.‘.[['II1:]l.IEll'l Mechanism
`
`Ap-pIicaI.ion.s
`Chemical Lasers
`
`Geiierai Description
`Laser StrL:c1ui'e
`Excitation Mechanism
`
`Applications
`14.3 K-Ra} Plasma Lasers
`Introduction
`
`Pumping Eiiergy Requirements
`Excitation Mechanism
`
`Clptical Cari ties
`X—Ra3r Laser Transitions
`Applications
`14.4 Free-Electron Lass.-rs
`Introduction
`Laser Structure
`
`Applications
`H‘.IEF"EII‘.I'.‘NE'I7.S
`
`15 LASER SYSTEMS INVOLVING HIGH-DENSITY GAIN MEDIA
`{:4-‘t-itn-'IE'i-.'
`
`15.1 flrganic Dye I.ascrs
`Introduction
`Lass: Suiicture
`E'.tcitaI:ion Meciianism
`
`Applications
`15.2 Solid-Stittt-Lasers
`I11IIodLtction
`
`5ICI
`5113
`5] I
`
`5II
`5ll
`515
`
`515
`516
`
`516
`51'?
`5] H-
`
`52.0
`520
`521]
`521
`
`522
`522
`
`522
`52!-
`523-
`
`52-‘!
`524
`
`524
`524
`514
`
`525
`525
`525
`
`52.5
`52.3
`
`532
`532
`532
`535
`535
`536:
`
`53?
`53?
`
`539
`539
`
`539
`539
`5-1-I]
`543
`
`544
`545
`545
`
`

`
`Juli
`
`itflvy Inn
`Gencnl Dcacripliun
`Laser Srucmn:
`Etduim Hoduanism
`
`Applkuim:
`Nu.-odylim Tall mi Elms Ina:
`Genenl Dcuzriplinn
`I..au Snrturc
`Enciluiun Mn:lunism
`
`Applicuicm
`Nu-d3rflIn:YI.l" lmscn
`General Dtmipliou
`Laser 5-I'I.|I:tl.ll'I!
`En-.'.iI.-uion Pvhduninm
`
`Applimtiuns
`N1-od31iI|n:'|"IiriIn1 1-‘uId:IelNd:'£\"tLlLIBIf5
`G-m:ntD¢-m1'pI.im
`Ln.-act Slruetunr
`Exciinl-.im Hachaninm
`
`Appliwims
`\"IIerhlum=l'a'uG Lnsml
`
`Genera! DnA:r'|.pI.iun
`Luca: Slnmlum
`Exduflun Mnclunism
`
`Applications
`Alexundfllu Lam.-r
`
`General Description
`Luscr Slnwum:
`Exdlauiun Mocluoism
`
`Application:
`Tluflum fiuppflu Lmer
`Gcnufl Dnmriptinn
`LU-III‘ SInn:tnn.-
`Excitation Mudunism
`Appliuciolu
`(‘Irwin LISJIF ad IJCJIF Laser:
`
`-Semen] Description
`Lucr 5I1.I:lun:
`Emitiion Madunllm
`
`Appiicnsiuuns
`Flu-r Inn-r:
`
`Gm-an] Dcuripliun
`[mar 5I"Id:l.ll'C
`Eaucislinn Medumllm
`
`Applicuions
`Culnr Cum.-r lam.-n
`
`Gencnlflwzriytion
`laser Sncturn:
`
`54?
`54'?
`
`549
`550'
`55!}
`55 I
`553
`554
`555
`
`5-56
`556
`55'}
`S5?
`55'?
`557
`553
`553
`559
`559
`
`563
`
`5'? I
`5? I
`5T2
`ST3
`5?3
`5'?!
`
`

`
`XII’?!-I
`
`CONTENTS
`
`Excitalj on Mechanism
`
`Applications
`15.3 Semiconductor Diode Lasers
`Inlroduefien
`
`Four Basic Types of Laser Materials
`Laser Sll'LE12 rure
`
`Fnxluencg-' Control ofLasea' Eluipul
`Quantum Cascade Lasers
`p-Doped Gennanium Lasers
`Excitation Mechanism
`
`Applications
`REFERENCES
`
`5ECT'|CI-H 6. FRE-EHJEHCY MU].T1‘Pt|EATlO|'i| OF LASER BEAM!
`15 FREQUENCY MULTIPLICATJGH OF LASERS AND OTHER
`NONHNEAR OPTICJIL EFFECTS
`nvelmew
`
`16.1 "Wave Propagation in an Aniautivapic Crystal
`16.2 Pohrizatintl Respmlfie of‘-'1a1e{'ia13 In Light
`16.3 Secnml-Order Nonihlear Optical Processes
`Second Harmonic Generation
`
`Sam and Difference Frequency Generation
`Optical Pa.ra.1'net:I'i-: flseillatien
`16.-I Third-flrder Nolllinear Optical Processes
`Third Harmonic Generation
`
`lnlensily-Dependeni Refractive Index — S-elf—Foc1.1.sEng
`16.5 Nonlinear Optical Materials
`16.6 Phase Matching
`Descli plinzrn cufl-"|:|a.se Matching
`Achieving Phase Malrhing
`Types of Phase -.'vInr.eh1' ng
`16.? Saturnble Abacnrptioa
`1IS.8 Two-Phalon Absorption
`16.9 Stimulated Raman Scattering
`16.10 Harmonie Generation in Gases
`REFERENCES
`
`Appendix
`Index
`
`5'34
`
`5'?-‘E1
`5'?-Ea
`5'?-Ea
`
`5'19
`SE!
`
`591
`592
`S94
`594
`
`596
`59'?
`
`(SDI
`5111
`
`501
`603
`604
`504
`
`5115
`E-D‘?
`50'?
`608
`
`509
`fill]
`{SID
`610
`{:13-
`615
`{:15
`61?
`613
`«G19
`I519
`
`62!
`525
`
`

`
`1 I
`
`ntroduction
`
`CI°Ir"ER"|rI'lE‘I"r‘ A laser is a device that amplifies light
`and produces a highly directional. high-intensity
`beast that most often has a very pure frequency or
`writ-eler1grh_ It comes in sizes ranging from approx-
`imatcly one tenth die diameter of a hurrtan hair to
`the size of a very large building. in powers ranging
`from l{l"9 to Ill?” ‘W, and ir1 wavelengths ranging
`fromthe microwave to the sot't—X-ray spectral regions
`with corresponding frequencies from 10" to ID” Hz.
`Lasers have pulse energies as high as ID‘ J and pulse
`durations as short as 3 3-: HT“ s. They can easily
`drill holes in the rn-oat durable of materials and can
`
`
`
`weld detached retinas witlrin the humareye. Tlrey are
`a lcey component of some of our most modern com-
`munication systems and are the "phonograph needle"
`ofour compact disc players. They perfonn l1ealI.1'e:rl-
`mentofhiglr-strengtlr materials. such as die pistons of
`our automobile engines. and provide a. special surgi-
`cal ltnife for rnanytypes of n1edlc.=rlprocedLrr'es_ They
`actastargetdesignators for military weapons and pro-
`vide -for the rapid checlt—out we have oorrre to errpect
`at the supermarket. What a remarkable range of char-
`acteristics for a device that is in only its fifth der'ade
`ofeiristence!
`
`INTRODUCTION
`
`There is nothing magical about a laser. It can he thought of as just another type
`uf light source. It ucrtnlrrly lies Lrrurry l.Elt.ll.]l.it.' E.|'t.LPp'.'.'.ILl.t.t:i tlrnt rrrnlu: it at special liglrt
`source. but these properties can be understood without knowledge of sophisticated
`mtulrcrnatical techniques or cernplerr ideas. It is the objective of this test to explain
`the operation of the laser in a simple. logical approach that builds from one con-
`cept to the next as the chapters evolve. The concepts, as they are developed. will
`be applied to all classes of laser materials. so that the reader will develop a sense
`of the broad field of lasers while still acquiring the capability to study. design, or
`simply rmderstand a specific type of laser system in detail.
`
`DEFINITION OF THE LASER
`
`The word laser is an acronym for Light Amplification by Stimulated Emission of
`Radiation The laser rnalt-es use of processes that incosase or amplify light signals
`aflertlrose signals have been generated by other means. These pro-cessm ioclude
`(I) stimulated emission. a natural effect Iliat was deduced by considerations re-
`lating to Ilremrodyrrarrrzc equilibrium, and [2] optical feedback {present in most
`
`

`
`INTIIODUCTEOH
`
`Optical resonator or cauily
`
`
`
`Figs! 1-1 Sirnplified
`schematic oftypical laser
`
`Fully ralleeting
`nirrar
`
`Parllally Ira-1a1i1IIn5
`rlirrar
`
`lasers) that is usually provided by mirrors. Thus, in its simplest fonn, a laser con-
`sists of a gain or amplifying medium {where stimulated emission occurs), and a
`set of mirrots to feed the light back into the amplifier for continued growth of the
`developing beam. as seen in Figure 1-I.
`
`5IltIlPI.lCl"|'Y OF A LASER
`
`'I'he simplicity ofa laser can be understood by oonscideri ng the light from a-candle.
`Normally, a buming candle radiates light in all directions, and therefore illumi-
`nates ‘various objects equally if they are equidistant from the candle. A laser takes
`light that would norrnally be emitted in all directions, such as from a candle, and
`concentrates that light into a single direction. Thus, ifthc light radiating in all di-
`rections from a candle were concentrated int;o a single beam of the diameter of tl1e
`pupil of your eye {approximately 3 min). and if you were standing a distance of
`l m from the candle.l]1-en the light intensity would be I,I‘.ll]O,E[:'l‘.] times as bright as
`the light that you normally see radiating from the candle! That is essentially the
`underlying concept oftlae operation of a laser. However. acandle is not the kind of
`medium that produces amplification. and thus there are no candle lasers. It takes
`relatively special conditions within the laser medium for amplification to occur,
`but it is that capability oftaking light that would normally radiate from a source in
`all directions — and concentrating tl1a1 light into a beam traveling in a single direc-
`Iion— that is involved in rnalcing a laser. These special -conditions. and the media
`within which they are produced. will be described in some detail in this book.
`
`UNIQUE PROPERHES OF A LJLSER
`
`The beam of light generated by a typical lasercan have many properfies that are
`unique. When comparing laser propezfies to those ofother light sources, it can
`be readily recognized that the values of various parameters for laser light either
`greatly exceed or are much mone restrictive than Ilse values for many common
`light sources. We never use lasers for street illumination, or for illumination within
`our houses. We don't use them for searchlights or flashlights or as headlights in
`
`

`
`ENTIIIJDUCHDN
`
`our ears. ‘Lasers general}; have a narrower frequent}-' disuibution, or much higher
`intensity. or a much gealer degree oI oollimation. or much dtorter pulse duration.
`than that avaiiable from more oornrnon types of light sources. Therefore. we do use
`thorn in oompact disc piajrers. in superrllarltet chock-out scanners, in sunr-e}ring in-
`stm meats. and in medical appiioalions as a surgical knife or for welding detached
`retinas. We aiso use thorn in cornmunioati-ons systems and in radar and rnililary
`targeting appiicalions, as well as rrlarly olher areas. A Eager is a specialized light
`source that should be used only when irs unique properties are required.
`
`THE LASER SPECTRUM AND WAVELENGTH5
`
`A portion ofthe e1eotI'on1agI1etic radiation spectrum is shown in I-7Ig1.tre 1-2 for the
`region covered by cunenfly -existing lasers. Such lasers span the wavel-englh range
`from the far infrared part ofthe speotrurn (.1 = I_C|Dfl am} to the s>orfl—}IL—ray region
`(1. = 3 nm}. thereby ooreri ng a range of wavellenglhs. of almost six orders oFrnag-
`nilude_ There are several types of unils that are used to define laser wavelengths.
`These range from rniommetersormiorone {am} in the infiared to nanometers [nun]:
`and angstroms {23L}'jn the visible. ultraviolet [LTV'"_I. vacuum uitI'a1.'ioIet{\"'U"H, es-
`treme uitraviokt (ELTV or KLFV]. and so1't.—X—ra}I ISXR} spectra] regions.
`
`WAVELENGTH UI|lI'|'5
`
`lam : I04‘ rn;
`1.-\:lD"°m;
`1nrn=1l]'9 m.
`
`Consequently. ] 1'I'|.iCH2|-!1[,t.t.I'EI} = IIJJIINI} angstroms bar] = ].DCl}nanomeIera{n.n1}.
`For esarupie. green light has a wavelength of S x H14 rn : 0.5 run : iflflflrit :
`500 nm.
`
`HF
`
`CD
`
`_aa2e__..>ee
`Ar
`..
`
`..
`
`N2
`Ruby
`srf
`He-Ne
`Md"'I'.¢lG
`Hn.[_:r|
`
`I
`.F|FI1.::.qr;.
`.._..
`
`Soft-I-Flat.
`1959:;
`...
`.. .
`
`Figure 1-1 Wavolerrgth
`range cI§VarioLei lasers
`
`co?
`
`Hs—h’e
`
`:
`
`_o_q;an§;:o.m_
`nrr
`Tm_.Ia03
`SM N-Pays
`Uhlelwolel
`"|'iseb5a
`Irtlrured
`Ear Infrared
`:_.....j.._r____ II __l..__.j__:j'______._
`Bflpm
`room
`3pm
`1pm 3DEInm 10Dnrn
`3tJnm ttlnm
`4
`IL—----
`
`——- ENERGY - ..
`
`

`
`INTRODUCTION
`
`WAVELENGTH REGIONS
`
`Far infrared: ID to l.0Clll J'..[.lTI'_.
`middle infrared: I to I'll t.[.ITI‘__
`near infrared: 0.? to lj.tI'n;
`visible: {L4 to ll.'i" itm. or 401] to Tllll nm:
`ultraviolet: 0.2 to I14 pm, or 200 to 400 nm:
`vacuurn ultraviolet‘. £l.I to {L1 trim. or 104} to 2.01] nn1:_
`extreme. ultraviolet: I'll to 10ll nmj.
`soft X-rays:
`I ntn to approximately 20-30 nm tsorne overlap with EUVL
`
`A BRIEF HISTCIIIY OF THE LASER
`
`Charles Townes took advantage of the stimttlated emission process to construct a
`microwave amplifier, referred to as a rnaser. This devioepmduced a coherent beam
`of microwaves to be used for communications. The first maser was produced in
`ammonia vapor with the inversion between two energy levels that produced gain at
`a wavelength of 1.25 cm. The wavelengths produced in the maser were compara-
`ble to the dimensions of the device, so extrapolation to the optical regime — w'here
`wavelengths were five orders oi'rr.agniti.tde sn1aller— was not an obvious extension
`of that work.
`
`In I958. Townes and Schawlow published a paper concerning theirideas about
`extending the rnaser concept to cptical frequencies. They developed the concept
`of an optical arnplitier surrounded by an optical mirror resonant cavity to allow for
`growth of the beam. Townes and Schawlow each received a Nobel Prize for his
`work in this field.
`
`In I9t'iI|.'.'I, Theodore Maiman :3! Hughes Research Laboratories produced the
`first laser using aruby crystal as the amplifier and aflashlamp as the energy source.
`The helical Hashlamp sunoundeda rod-shaped ruby crystal, and the optical cavity
`was formed by coating the fiatterued ends of die ruby rod will‘: a lighly retlecting
`material. An intense red beam “as observed to emerge from the end of the rod
`when the flashlarnp was fired!
`The first gas laser was developed in I9fi| by A. Javan, W. Bennett. and D. Har-
`riott of Bell Laboratories. using a 1'l1l.T.lIlI'E of helium and neon gases. At Ilte same
`laboratories, L. F. Johnson and K..NEassau demonstrated the first nendytuium laser,
`whichhassince become one olthe most reliable lasers available. This was followed
`
`in 1962 by the First serniconductv:-r laser. dcroonslsated by R. Hall at 1:he General
`Electric. Research Laboratories.
`in 1963. C. K. N. Patel ofBelI Laboratories dis-
`covered the infrared carbon dioxide laser, which is one ofthe most eflicient and
`powerfiil lasers available today. Later that same year. E. Bell of Spectra Physics
`discovered the first ion laser. in rrercory vapor. In 1964 W. Bridges of Hughes Re-
`search Laboratcries diseovered the argon ion laser, and in I96-6 W. Silfvast. G. R.
`Fowles. and B. D. l-loplcins prodt-oed the first blue heliui:n—cadn1iurn metal vapor
`
`

`
`INTRODUCTION
`
`laser. During that same year. P. P. Soaoitin and I. R. Lanlrard of l]re IBM Research
`Laboratories developed the Iirst liquid laser using an organic dyedissolycd in a sol-
`vent, thereby leading to the category of broadly tunable lasers. Also at that time,
`W. Walter and oo-worlszers at TRG reported the first copper vapor laser.
`The tirst vacuum ultraviolet laser was reported to occur in mo-lecuiar hydro-
`gen by R. Hodgs-on of [EM and independently by R. Waynarit eta]. of the Naval
`Research Laboratories in 1"El"i'l]. Tire lirst of the well-l<rr-own rare -gas-—halide err-
`cimer lasers was observed in xenon fluoride by I. J. Ewing and C. E-rau of the
`rltvco—Eyerett Research laboratory in I915. In that same year, the lirst quantum-
`well laser was made in a gallium arsenide semiconductor by J. van der Zlel and
`co-workers at Bell Laboratories. in 19".!’-IS, J. M. I. Madey and co-workers at Stan-
`ford University demonstrated the first free-electron laser amplifier operating in the
`infrared at the C0; laser wavelength. in I979, Walling and co-workers atfitllied
`Chemical Corporation obtained broadlyturrable laser output liroma solid-state laser
`material called aiexarrdri te. and in I985 the frrst soft—X—ray hrscr was successfully
`demonstrated in ahighly ionized selenium plasrnahy D. Matthews and a largenr.rm-
`ber of co -workers at the Lawrence Livermore Laboratories. In 1936, F‘. l'v‘[oulton
`discovered the titanium sapphire laser. In I991, 1'r-'l. Hasse and co—worl~'.ers devel-
`oped the first blue -green diode laser in ZnSe. In I994. F. Capasso and co-workers
`devetoped the quanttrm cascade laser. In I995. 53. Nakarnura developed the first
`blue diode laser in GaNJ:aased materials.
`
`In l96l, Fox and Li described die existence of resonant transverse modes in
`a laser cavity. That same year. Boyd and Gordon obtained solutions ofthre wave
`equation for confocal resonator modes. Unstable resonators were demonstrated
`in 1969 by Krupke and Sooy and were described theoretically by Siegrnan. @-
`switcliing was first obtained by ]'|r"IcClrrng and