LASER FUNDAMENTALS
`
`SECOND EDITION
`
`WILLIAM T. S!LFVA5T
`
`School of Optirj J" CRECIL
`Unfvershy of Central Florida
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`CAMBRIDGE
`IINIVERSITY PRESS
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`First published I996
`RE1'.|I'il'lI.BEI I999. ZDDD. EIIIG
`
`First edition EOCamIJ|'idge I.iniI.'arsiitg.' PIES
`S-Bound e£iidI:n1Ei1 Wiliiflm T. Silfimt 3134
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`This book is iI1i:.o1:yJ"|fl|l_ Subject In stajulnry exceptiun and
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`Fi.I'5t|n.Ii1li5hed 2001
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`Printed in line United 513250!’ Ainerica
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`Tfqagfaca Ti|1:n=_-5 1D_5|r!l.5 and mlmir
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`A aalntag ra'wn:i'J'i:Ir liar".-.' booth awriiabiefmm the Hririnh i'..I'brr.rr_v_
`
`Lfbmry of Comgran Chraiogiiug in Fubificarion ahm
`Silfvast. '|h"II|:ia|:n 'I'I1mI'I.'a5.1*§|.'5TI'—
`Lansaer Iundamerlalsfwilliarn T. Siilfvast. — 2nd ed.
`:1. ma.
`lneiudas bitIIii:gJ'a_i3hic-ai .l'EfB2l'H'I£!B5- and iddacu.
`ISBN 0-521-53345-0
`I. Lasas.
`I. ‘F53.
`
`IIIDI
`TAIEr'J‘5.S52
`I5ll_3I5"1‘S — d£"Z1
`
`ISBN III fill E33-I5 III hardback
`
`1003055352
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`

`
`page xix
`xxi
`
`uiii
`
`LI:-I'i-L.n'|t\.a'Ih.l————
`
`Contents
`
`Preface to the Second Edirion
`
`Prefiice to the Fir.'ri' Editioir
`
`.-tcicnowiedgments
`
`1
`
`INTRDIJUCTION
`D'II'EII‘.\I']E'H'
`introduction
`Definition of the I..aser
`
`SinIpIieit_v Illa laser
`Unique Properties of :1 Laser
`The Lasler Spectrum and ‘r‘\~':-welcrtgtlts
`A Brief Hislor'_r ntthe Laser
`Overview‘ of the Iluoli.
`
`SECTION 1. FUND.AMENTAL WAVE PROPERTIES OF LIGHT
`
`2 WAVE NATURE OF LIGHT — THE INTERACTION CIF LIGHT
`WITI-i IHIATERJALS
`D'Ii'EII‘.\I']E'I't'
`
`2.] Maxwt-lI’sFA11tatiun5
`2.1 .‘t'Ia3m'eil’5 ‘I'r'art- Equafions
`MaJtweIl'5 Wave Equations for a Vacuum
`Solution of the General Wave Equation — Equivalence of Light and
`Electromagnetic Radiation
`Wave ‘Velocity — Phase and Group Veiocities
`Gcncmiired Solution of Lhe Wave Equation
`Tft1i't.S'\-E!'.SE Electromagnetic Waves and Poiarizcd Light
`Flow of Eieetro-magnetic Energy
`Radiation from a Point Source (Electric Dipole Radiation‘:
`2.3- Interaction of Electmniagpteiic Radialiu:1{Lig!Itt with ]"I-laltt-r
`Speed of Light in 3 Medium
`Maxwell's Equations in a Medium
`Application of ]'L-Ia.xwe1l's Equations to Dielectric Materials —
`Laser Gain Media
`
`Complex Index of Refraction — Optical Constants
`Absorption and Dispersion
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`
`viii
`
`CONTENTS
`
`34
`315
`3'?
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`39
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`43
`43
`45
`-15-
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`49
`5 l
`54
`54
`54
`S15
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`57
`57
`59
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`I53
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`67"
`IS?
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`I59
`'31]
`TD
`72
`72
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`Estimating Particle Densities ofllu-laterials for Use in the
`Dispersion Equations
`2.»! Coherence
`
`Temporal Coherenoe
`Spatial Coherence
`REFERENCES
`PIUBLFJIS
`
`SECTION 2. FLl]'~lDAltIlE1'~lTAL QUANTUM PRCIPEENES OF LIGHT
`
`3 PARTICLE NATURE OF LIGHT — DISCRETE ENERGY LE"t'ELS
`DVERVIEW
`
`3.1 Bohr Theory 0!‘ the I-lydrogen Atom
`Historical Development of the Concept of Discrete Energy Levels
`Energy Levels of the I-llydro-gen Atom
`Frequency and Wavelength of Emission Lines
`Ionization Energies arid Energy Levels oflons
`Photons
`
`3.2 Quarttum Theory of Atomic En-ecrgy Levels
`Wave Nature oI'Pa.rLie1es
`
`Heisenberg Unoentainty Principle
`Wave Theory
`Wave Functions
`Quantum States
`The Schrodinger Wave Equation
`Energy and Wave Function for the Ground State of the
`Hydrogen Atom
`Excited States of Hydrogen
`Allowed Quantum Nurnhers for Hydrogen Atom Wave Functions
`3.3 Angular ll-'Iomentu.m ol' Alorns
`Orbital Angular Momentum
`Spin Angular Momentum
`Total Angular Momennim
`3.4 F_I1e:rgt' Levels Assn-cinted with Dne-Elechwm Atoms
`fine Structure ofSpeoI.ral Lines
`Pauli Exclusion Principle
`.l-.5 Pe:ri-odic Taltle ofthe Elements
`
`Quantum Conditions Associated widt Multi pie ElEI£.'.lIDllS Attached
`to Nuclei
`Shorthand 2*-lotation for Eleeuonie Configurations of Atoms Having
`More Than Doe Electron
`
`3-.6 F.nerg_I.' I.-evels ol‘ I1-'Itdi.i-FJL-ctron Atoms
`Energy—Le~.rel Designation for It-luIti—Eleetron States
`Rus.5ell—Saunders or L3 Coupling — Notation for Energy Levels
`Energy Le've.l5. Associated with Two Electrons in Unfilled Shells
`Rules for Obtaining S, L. and J for L3 Coupling
`fieneraey and Statistical Weight:
`Coupling
`Isoelectronic Scaling
`
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`

`
`CONTENTS
`
`REFEIENCFS
`FEDBLEII-‘IS
`
`4 RADIJIITNE TRANSITIDNS AND EMISSION LINEWIDTH
`D'l:'E.R‘l"]E‘H'
`
`-l.1 Decay o:I' Excited States
`Radiative Decay of Eircited States of Isolated Atoms —
`Spontaneous Emission
`Spontaneous Emission Decay Rate — Radiative Transition
`Probability
`Li feti me of a Radiating Electron — The Electron as a Classical
`Radiating I-[arrnonic Oscillator
`Nonrad.iaI:ive Decay of the Excited Slates — Collisional Decay
`4.2 Eltllflfiiflll Bet:-adcn.ing and [iinevridtlt Due to Rarfratiw Decay
`Classical Emission Linewiddt of a Radiating Electron
`Natrrral Emission l_.l!|'J.t‘.'Wl'l2II.l'l as Deduoed by Quanttrrn Mechanics
`{Minintum Linewidtlt}
`-Ll Additionrd Enrissiusr-Broadening Processes
`Broadening Due to ."~lortradiative {lfollisionalt Decay
`Broadening Due to Dephasing Collisions
`Arnonnhous Crystal Broadening
`Doppler Broadening in Gases
`Voigt Linesltape Profile
`Broadening in Gases Due to Isotope Shifls
`Comparison of Various Types of Emission Broadening
`-I.-II Quantum Mechanical Description of Radiating Atoms
`Electric Dipole Radiation
`Electric Dipole Mani: Element
`Electric Dipole Transition Probability
`Oscillator Strength
`Selection Rules for Electric Dipole Transitions Involving Atoms
`with a Single Electron in an Untill-ed Sl.Il'|S.l'IBIl
`Selection Rules for Radiative Transitions Involving Ato ms with
`More Tltan One Electron in an Unlilled Sulzrsltell
`
`Parity Selection Rule
`lrtofficienr Radiative Transitions — Electric Quadrupole and Crdrer
`Higlter-Order Transitions
`I‘.E.l-'ERENCFS
`Fttottntrr-ts
`
`5 ENERGY LEVELS AND RADIATNE PROPERTIES OF MCILECULES.
`LIQUIDS. AND ‘SOLIDS
`{wE.tr‘vt£'IIt'
`
`5.1 llrlrtlecrllar Energy Levels and Spectra
`Energy Levels of Molecules
`Classificanon of Simple Molecules
`Rotational Energy Levels of Linear Molecules
`Rotational Energy Levels of Sym met:ric—Top Molecules
`Selection Rules for Rotational Transitions
`
`36
`SIS
`
`39
`89
`
`N33
`lU5
`lflti
`ll}?
`I09
`109
`I14
`ll5
`I13
`I21
`122
`l23
`l2-'-I
`l24
`
`I29
`13!]
`
`l3]
`l3l
`l3l
`
`l35
`l35
`l35
`i35
`ll?
`139
`Ml
`lrl-I
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`
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`

`
`EDHTEHT5
`
`Vibrational Energy Levels
`Selection Rule for ‘I.-"il:Irstiona1 TriI.nsilions
`RotaLional—‘|."ibrational Transitions
`Prolzlnali-i].i1ies of Rotational and Vibrational Trsnsilions
`
`Electronic Energy Lerels of Molecules
`Electronic Transitions and Associated Selection Rules of
`Molecules
`Emission Lineuxidth ofMoleca1a.r Transitions
`
`The Franclt—CorLdon Principle
`Escimer Energy Le~.'e_~'.
`5.2 Liquid F.rLr.-rgy I.an'els and Their Radiaiien Prrrperfies
`5I:n.M':ture of Dye Molecules
`Energy Levels ofDyeMo1ecules
`Excitation and Emission of Dye Molecules
`Detrimental Triplet States ofDye Molecules
`5.3 F.]'l'EI‘g}' Leycis in fluids — Dielectric Laser .‘+'laleri:nls
`Host ll-‘.lateriaJs
`
`Laser Species — Dopanl Ions
`1'”~la.rro~:.'-Linevi.'itltJ1 Laser Materials
`Bro.ai:|ba.nd Tunable Laser Materials
`
`Brosderting Mechanism for Solid-State Lasers
`S.-I Energy Lei-'eIs in Solids — Semiconductor Laser Matt.-risk
`Energy Bands in Crystalline S-oLids
`Energy i_.evels in Periodic S1:ructures
`Energy Levels of Conductors. Insulators. and Seniiconductors
`Excitation and Decay ofEJtciled Energy Levels — Reoombinarion
`Radiation
`
`Direct and Indirect Eandgap Semiconductors
`Electron Distribution Function and Density of Slates in
`Semiconductors
`lntri nsic Semiconductor Malenals
`
`E:r.I3'in_sio Semiconductor Materials — Doping
`p—.'n Junctio-:15 — Recombination Radiation Due to Eleclrical
`Eircitali on
`
`Heterojuncliori Semiconductor Materials
`Quantum Wells
`Variafion of Eandgap Energy and Radiation ‘Wavelength with
`Alloy Composition
`Recombination Radiation Transition Probability and Linewidth
`REFE|IENCE5
`PllDIl1.EMS
`
`E R.hDlAT|ON AND THERMAL EGLIILIBRIUM — ABSORPTION AND
`STIMLILATED EMISSION
`OVERVIEW
`
`-15.1 Equitiliriuna
`Tl'1ern'Jal Equilibrium
`Thermal Equilibrium via Conduction s.nd Convection
`Theraial Equilibrium. via Radiation
`
`143
`143
`144
`145
`149
`
`150
`15!]
`ISI
`152
`153
`153
`155
`156
`15?
`153
`153
`159
`115-1
`166
`16-3
`163
`16-3
`1'.I'D
`1T2
`
`1TI'3
`1714
`
`1?5
`1?‘?
`J T9
`
`132
`[E4
`136
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`191
`195
`195
`195-
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`199
`199
`199
`199
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`xi
`
`EDI
`204
`20-5
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`H 2
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`07
`203
`209
`2 [D
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`21|
`214
`215
`216
`21?‘
`22|
`El
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`225
`225
`225
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`225
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`229
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`230
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`23 I
`232
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`233
`234
`E35
`233
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`233
`MI
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`W 3
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`45
`24'?
`24'?
`243
`249
`253
`253
`
`CONTENTS
`
`6.2 Radiating Bodies
`Snela.n—Bolt2.mann Law
`Wien's Law
`ll.'I“3EllB:|'llZ'C and Radiance
`
`l.'i.3- Cavity Radiation
`Coo nling the Number of Cavity Modes
`Ra}rleigh—.|eans Fonnula
`Planck‘: Law for Can-'it}r Radiation
`Relationship between Ca1.'ir_',r Radiation and Blax:1:l:rod'_I,'
`Radiation
`
`Wavelength Dependence of Elaekbody Ernissi on
`lir.4 Absorption and Siimulated Emifiion
`The Principle of Detailed Balance
`Absorption and Stimulated Emission Co-effieients
`REFERENCES
`I'I[HlLE!o'IS
`
`SEETICIH 3. LA.5E|1AlIlPLlFlERS
`
`F CONDITIONS FOR PRODLICING A LASER - PCIPU LATIGN
`INVERSIDHS. GAIN, AND GAIN SATURAT ION
`{i'l:"EIl‘|"]E‘H'
`
`.-'l.hso11:-tion and Cain
`'J'.l
`Absorption and Gain on a Hornogeneously Broadened Radiative
`Transilion {Lo-rentzian Frequency’ Disuibulion}
`Gain Coefiieient and Sli rnulated Emission Cross Section for
`
`Homogeneous Broadening
`Absorption and Gain on an !nhornogerLeoLLsi3' Broadened Radiative
`Transili on [Doppler Broadening wifln a Gaussian Distribuli onl
`Gain Coellieient and Sti rniilated Emission Cross Setaion for
`
`Doppler Broadening
`Statistical Weights and line Gain Equation
`Relationship of Gain CneFficient and Sti Irniialed Emission
`Cross Section to .!L‘o.=:orpI:i on Coeffieient and Absorption
`Cross Section
`
`Tl Population Inversion 11"-'e<:essar1.' Condition for a laser]
`'!.3- Saitzrafion Intensity ifiuflicienl Condition for a Laser]
`'..".4 Dewelnplnenl and Growth ofa Laser Ilealn
`Growth of Beam for a Gain Mediunt with Homogeneous
`Broadening
`Shape or Geonlelry of Amplifying Medium
`Grou.1l1 of Beam for Doppler Broadening
`"L5 Exponential Growth Factor {Gain}
`T.IS- Thrieshulnl Requirenients for a Laser
`Laser with No Mi.I1'ors
`Laser with One Mirror
`Laser with Two Mirrors
`ILEEEEENCES
`I'Il}ILEl'o'IS
`
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`

`
`xii
`
`CONTENTS
`
`LASER DSCILLATIDN ABOVE THRESHOLD
`DVERVIEW
`3.1 Laser Cain tiaturalion
`
`Rate Equations of the Laser Levels That Include Stimulated
`Emission
`
`Population Densities of Upper and Lower Laser Levels with
`Beam Present
`
`Small-Signal Gain Coefficient
`Sanitation of the Laser Gain ahoi-we Tliresliold
`
`3.2 Laser Beam Growtil he}-ostd the 5.-liuralio-it I]]lI£‘l'I5il'_|.'
`Change from Ex portontial Growth to Linear Growth
`Steady-S Late Laser Intensity
`3.3 Optilnizratitln u-I'l.:tser Output Power
`flptimum Output Mirror Transmission
`flptimum Laser Dutput intensity
`Estimating flptirnum Laser Dutp-ut Power
`5.4 F_nesrg1.- Eitciiange ii-etw-een Upper La.-ser Level Population and
`Laser Photons
`
`Decay Time ofa Laser Beam -.I.-'[Il1in an Optical Cavity
`Eaaiit; Laztel Cavity Rate Equaliulia
`Steady-S tate Solutions heiow Laser Threshold
`Steady-S tate Elperali on above Laser Threshold
`H5 Ixaser Output Flur.'ttIat.ioiis
`Laser Spflring
`Relaxation flseillations
`
`3.6 Laser fitmplifleqs
`Basie Amplifier Uses
`Propagation of a High-Power. Short-Duration I.'J'pI:ia:a.l Pulse through
`an .r'-tmplifier
`Sanitation Energy Fluenoe
`Amplifying Long Laser Pulses
`Amplifii ng Short Laser Pulses
`Comparison of Efficient Laserfitmpiifiers Based upon Ftinclarnental
`Saturation Limits
`
`El-'iin'or Array E.l'H2I Resonator [Regei1eratii'ej.I5.mpIiIiers
`REFERENCEE
`PJIDELETVIS
`
`REQUIREMENTS FOR OBTAINING POPULATION INVERSIDN5
`DVEHWEW
`
`9.1 Im'ers'Ions and Two-I.ei.'t.-I S-‘_|-'StI£‘l'tlS
`9.2 R£'I‘¢1'I2i'i-‘E Decay Rates — Ratiiative versus Collisiooal
`9.3 Steady‘-State Im'er.~ions in TIimee- and Four-i.ei'ei Systertis
`Tllree-L.ei'eI Laser with die Inten1iedinteLei'eI as the Upper Laser
`Lei-‘e1
`
`TI'Lreo-L.ei'eI Laser wifli die Upper Laser Level as the Highest Level
`Fnur—Let-'el Laser
`
`9A Transient Population II1irers.'ioIIi5
`
`255
`255
`255
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`255
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`256
`25?
`25?
`253
`253
`26!
`215-1
`215!
`215-4
`264
`
`266
`26?
`2GB
`220
`222
`223
`27'3-
`2215
`229
`229
`
`'1¢
`
`232
`234
`234
`
`235
`235
`283
`285.
`
`290
`290
`290
`292
`293
`
`295
`298-
`3!]!
`304
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`

`
`CONTENTS
`
`xiii
`
`9.5 Processes That l.nllil1'rt or lll’ESlZ]‘t'.|'_|p' Inrersinns
`Radiation Trapping in At-orn..~; and lons
`Electron Collisional Thermalization of the Laser I_.cve|s in Atoms
`and Ions
`
`Comparison :11 Radiation Trapping and Electron Collisionai Mixing
`in a Gas Laser
`
`.€|.bsorpIi on 1-.I.-'il.lIin the -Gain Medium
`IIEIFEEENCES
`PIICII-l.'EI|'t'IS
`10 LASER PUMPING REQUIREMENTS AND TECHNIQUES
`OVERVIEW"
`
`1ll.1 Excitafion or Pumping Threshold Requirements
`1ll.1 Pumping Pathways
`Excitation by Direct Pumping
`Excitation by Indirect Pumping [Pump and Transti'er‘.|
`Specific Pump-and-Tra.n.si'er Processes
`1ll.J- Specific Excitation Parameters Associated with
`Cllptical Pumping
`Pumping Ceornetn :35
`Pumping Requirements
`A Sirnplilied Optical Pumping Appro:Itim.at.ion
`Transverse Pumping
`End Pumping
`Diode Pumping of Solid—Statc Lasers
`C1'tE|IE|.I3l.EI'.lI.E.l.'lE|-l'I ofa Laser Gain Medium with Optical Pumping
`(Slope Efficiencjr)
`1ll.-'l- Specific Excitation Parameters Associated with
`Particle Pumping
`Electron Collisional Pumping
`Hear}.-' Particle Pumping
`A More Accurate Description of Electron Excitation Rate to a
`Specific Energy Level in a Gas Discharge
`Electrical Pumping of Semiconductors
`nasmtlmcas
`PIIGILI-'IMS
`
`SECTION 4. 'Lfit.SERfiE5'IJNJltTORS
`
`11 LASER C.Il."J'l'|'Y MDDES
`(]'h'Elt't-'|IE|'tI'
`11.1 Introduction
`
`11.1 I-ong'rluIiinaI Laser Ca1.'i1'_I.' Mules
`Fabr_',.'—Petot Resonator
`Fabr_',.'—Petot Ca".-'itj,' Modes
`Longitudinal Laser Cavity Modes
`Longitudinal Mode Number
`Requirements for the Development of Longitudinal
`Laser Modes
`
`30?!‘
`303
`
`31]
`
`315
`
`3115
`319
`3-19
`322
`3-22
`
`322.
`314
`324
`33'?
`33!]
`
`339
`33'}
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`346
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`
`352
`
`355
`355
`359
`
`359
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`
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`3?‘?
`330
`38!]
`
`381'.
`
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`

`
`xiv
`
`CONTENTS
`
`‘H3 Transverse Laser C‘a1'iI3' Modes
`FresrueI—Kirehhofl' Diffraction integral Fonn ula
`Development of Transverse Modes in a Cavity with Plane-Parallel
`Miners
`
`12
`
`Transverse Modes Uflng Curved Mirrors
`Transverse Mode Spatial Distributions
`Transverse Mode Frequealeies
`Gaussian-Shaped Transverse Modes within and beyond 1J1e
`Laser Cavity
`11.4 Pmperlies of Laser Modes
`Mode Characteristics
`Effect of Modes on me Cain Medium Profile
`EEFERENCES
`FRl}BLEl'r'IS
`STABLE LASER RESONATORS ARD GAUSSIAN BEAMS
`[H"El7l.‘¢-'lE'|'n'
`11.1 Stable 'E'u:n'ed Mirror Cavities
`Curt-13:1 Mirror Cavities
`AECD Matrices
`
`Cavity Stability Criteria
`11.2 Properties of Gaussian Beams
`Propagation ofa Gaussian Beam
`Gaussian Beam Properties t1fTtl-‘D-MiI1'EII Laser lfavities
`Properties of Specific Two-Mirror Laser Cavities
`It-‘lode Volume efa Herrnite—-Gaussian Mode
`
`11.3 Pmperlies of Real Laser Beams
`ll.-I Propagation of Caus5i:rI1 Beams |.;'-sirtgi-1.BCfl Matrices —
`Complex Bean: Parameter
`Complex Beam Parameter Applied to a Tu.-'o—!’t-'iirror Laser Cavityl
`REFERENCES
`PROBLEMS
`
`13
`
`SPECIAL LASER CA'uI"lT|ES AND CAWTY EFFECTS
`D‘l"Ell‘I|'Il-'."|'l'
`1.1.1 L‘ns1ableResona1urs
`
`13-.2 Q-Switching
`General Description
`Theory
`Methods of Producing Q-Switching within a Laser Ca'.'itj,'
`1.!-.3 Cain-Switching
`13.-I ]'t-lode-Inciting
`General Description
`Theory
`Techniques for Producing Mode-Locking
`13-.5 Pulse SIIorIeningTeelu1.iques
`Self-Plrase Modulatic-n
`
`Pulse Shortening or Lengthening Using Group "u"elocit}' Dispersion
`Pulse Compression {Shoneniag} with -Gratings or Prisms
`Llltrashort-Pulse Laser and Ampiifer System
`
`334
`385
`
`336
`390
`39!
`392
`
`393
`3'96
`396:
`39'?
`399
`399
`402
`492
`402
`-102
`
`4-ll]
`4|!
`4-I3
`4-I?
`42]
`423-
`
`425
`42R
`43 I
`431
`434
`434
`4-34
`439
`4-39
`44!
`
`450
`4-5!
`45!
`45!
`456
`462
`4153-
`
`465
`46?
`
`
`
`
`
`
`
`

`
`CONTENTS
`
`IV
`
`LLIS Ring Last-rs
`Monolidiiu: Unidirectional Sing1e—Mode Nd:‘I!'AG Ring Laser
`Tu.-'o—!'Ip'fjrror Ring Laser
`[3.T Contplex Beam Parameter .-5LI:|aI_1.'si'.s .-itpplied to Mu]l:i-Mirmr
`L39?!‘ IEa'-1'l'ne-.':
`
`'I"nree-Mirror Ring Laser Cavity
`Three— or Fu-Lir—M1'rror Focused Cavity
`[LLB Ca!-‘itit.-5 for Pmducing Spectral .‘H'a:n'o1n'ng of
`Laser Output
`Cavity wit]: Addifional Fabr}r—Perot Etzdon for Narrow-Frequency
`Selection
`
`Tunable Cavity
`Broadband Tunable cw Ring Lasers
`Tunable Cavity’ for UItrana1Tov.'-Frcqtuency Dutplut
`Distributed Feedback I{DF'B‘] Lasers
`Distributed Bragg Reflection Lasers
`l3~.9 l.a9e:r Cavilies Requiring S-mall-Dialm-ter Gain Regions —
`Asligjnafically Compensated C-‘d\'i‘lit5
`l3~.]l] ‘Wawgui-tie Cavilies for Gas [..ast-rs
`REFERENCES
`FIIGELEMS
`
`SECTION 5. SPECIFIC LIISER SYSTEMS
`
`1-I1 LASER SYSTEMS INVOLVING LOW-DENSITY GAIN MEDIA.
`fl'VE.II"r'IE1I'\I'
`t4.l Atomic Gas Lasem
`i.1't|IDdlJEttD1'I
`H+.-lium—N1.-on Laser
`
`General Descri plion
`Laser Stntolure
`Excitation Mechanism
`
`Applications
`Argon Ion Laser
`General Descri pli on
`Laser S1:n.Iu:'lLrre
`Excitation Mechanism
`
`Krypton Ion Laser
`Applications
`HI.-Iiu.m—CadmiuI:n Laser
`
`General Descri plion
`Laser S1:n.1otLtrc
`Excitation Mechanism
`
`Applications
`Copper "r'ap0r 1.35?!‘
`General Description
`Laser Stn.n:tI.I.re
`Excitation Mechanism
`
`Applications
`
`453
`459
`«HO
`
`-HE!
`4TB
`4T"3
`
`4?3
`
`4T8
`4T8
`480
`480
`4E|
`484
`
`484
`485
`45b
`488
`
`=.'.E'|I
`49I
`49I
`49I
`492
`492
`493
`4'34
`49".!‘
`49?
`49?
`498
`499
`5:00
`SDI
`SDI
`SUI
`302
`
`505
`505
`5-05
`507'
`507‘
`
`
`
`
`
`
`
`

`
`CONTENTS
`
`14.2 Molecular Gas Lasers
`lnlroduction
`Carl:-on Dioxide L:|:.-:cr
`
`General Dcsclipdion
`Laser Structure
`Excitation Machamsm
`
`Applications
`EII'.'Ii'I.]H' Lasers
`
`General D1;-rscripiion
`Laser Structure
`Excitation Mechanism
`
`Applicalions
`Niim-gen [..a5«H'
`General Description
`Lasex SITLL-E:'tIJi'n3 and Excitajion Mechanism
`
`Applications
`Far~1I1l'rJred Gas Lasers
`
`General Description
`Laser Slrucrurc
`Exc'itnI.ion Mechanism
`
`Applications
`(_'l1cmical 1.35:.-rs
`
`Gerieral Dc:-zcriplion
`Laser SIrI.Lc1.ure
`Excitation Mechanism
`
`Applications
`14.3 K-Ra} Plasma Lasers
`lnlroduction
`
`Pumping Eriergy Requirelri.-ants
`Excitation Mechanism
`
`Optical Cavifics
`X-533 Laser Transitions
`Applications
`14.-I Free-Elcctnm lasers
`Introduction
`Lasezr SI:n.LcL‘urc
`
`Applications
`REFERENCES
`
`15
`
`LASER SYSTEMS |I'WDL‘H'INE HIGH-DENSITY GAIN MEDIA
`D\-'E'.Il‘I.-'lE'H'
`
`'I5.I flrganic Dye I.:i-scrs
`Introduction
`Lascr S-IrI.:c1:ui'c
`Excitalion Mochariism
`
`Applications
`15.2 Solid-State Lasers
`Inlroduction
`
`SID
`SIC!
`5] I
`5] I
`5| I
`515
`515
`Slfi
`Slfi
`51'?
`5| E-
`520
`520
`52!]
`52I
`522
`522
`522
`523-
`523
`524
`524
`52.4
`524
`5114
`525
`525
`525
`525
`523
`532
`532
`532
`535
`535
`53-5
`53?
`53?
`
`539
`539
`539
`539
`5-1-1]
`543-
`5-14
`545
`545
`
`
`
`
`
`
`
`

`
`CHITEHTI
`
`Ruby Inn
`Gencul Dcncripliun
`Law Strucinn:
`Mndnni.Im
`
`Appiicdions
`N:-odpfluu I'M} and Chas I..Iu-rs
`Gmenl Description
`Laser Suncturc
`Emilalian Mudunisln
`
`Applicdiom
`Hmdyti-InI:l'I.l-‘ Lusen
`General Dcacripliou
`I.asur Slmctur-:
`En-.'.iIua'nn M?-eduuim
`
`Applicuicm
`Ntod3'|iIlI:'|"flrium Vnunudite 4 EN‘-:I:!'\"0;} Llfiffi
`General Dnwriplim
`Laser S1.nH.tun:
`Enciinlicm hiecluninm
`
`54?
`54'?
`
`549
`551'}
`550
`55 I
`553
`554
`555
`
`5515
`5515
`55?
`55?
`
`Applimtims
`\"IIerh|um=\':'lpL“. Lauri
`
`Genera! Dr.'u:r'|pI.iun
`Lunar Slxucture
`Excitation Mndunism
`
`Jlpplicltiuns
`Aleaumlrllu Lam‘-er
`
`General Description
`Lnicr Strucmre
`Exdlaubn Moclwrism
`
`Application:
`Tkniun fiuppfllv Laser
`Gama! Dwctipdun
`Laser Suwwrc
`Excituiun Hnchmism
`Applicuiuns
`Eimini LEAF ad I.ilL‘!LF Ln-III
`
`-|‘3en:n.l Dcscripfim
`l.In:I’ Scruaun:
`Eamillinn Mcdun'um
`
`Appliciions
`Fiber Ian-rs
`
`{Sen-nnl Duntripliun
`Lunar Sarncturc
`Excislim Mecharlism
`
`Applicaians
`Culnnr {.'I.-nu-r [mm
`
`Gencnl DH-I.‘I'i.]fliMl
`Laser Structure
`
`
`
`
`
`
`
`

`
`XV‘!HI
`
`CONTENTS
`
`Eatcitali on Mechanism
`
`Applications
`15.3 Semicontiuctor Diode L25-vEI‘S
`lntroclttction
`
`Four Basic Types of Laser Materials
`Laser Slrttcture
`
`Fn11Lt£:nc3r Control ofI_.a5e:r Dutpul
`Quantum Cascade Lasers
`p-Doped Gennanium Lasers
`Excitation Meci1aJ1isI'n
`
`Applications
`REFERENCES
`
`SECTION 6.. FREQUENCY MULTIPLICATION OF LASER BEAMS
`1.6 FREQUENCY MULTIPLICJLTIDM OF LASERS AND OTHER
`NONLINEAR OPTICAL EFFECTS
`D'I"ElH'IE'|'n'
`
`1I‘5.I "Wave Propagation in am Anistadmpic Cryslal
`16.2 Polarizztiimn Respmtse u-I' _'|r'latet1'aIs lo Liglti
`16.3 Second-Order Nu-nJinea.r U-piical Processes
`Second Harmonic Generation
`
`Sum and Difference Frequency Generation
`Optical Pa.ramet:ri-: Elsciilation
`16.4 Third-flrder Nnrllint-a.r Dptica] Pmcesses
`Third Harmonic Generation
`
`Intensity-Dependent Refraxztzii-e Lnciex — S-eif—Foct1sing
`16.5 Nonlinear Optical Materials
`16.6 Plntsc Matching
`Descli plio-rt ofPl1asc Matching
`Achieving Phase Matching
`Types ofPi1ase Matching
`16.? S:1lurablc.!i.b5nl1:Ition
`16.8 Two-Photon Absorption
`16.9 S!im1I.1:t{cd Ramon Scallerilug
`lIS.1l} Harmonic Generation in Gases
`REFERENCES
`
`Appendix
`Index
`
`5'II‘4
`5'?-‘E1
`5'?-Ea
`5'?-Ea
`5'3”?
`53!
`591
`592
`594
`594
`5'96
`59‘?
`
`51]!
`EDI
`5|]!
`(:0?!-
`
`62!
`62:1
`
`
`
`
`
`
`
`

`
`1 i
`
`ntroduction
`
`CN£R‘|rI'lE‘N A laser is a device that amplifies light
`and produces a highly directional. high-intertsity
`beam that most often has a very pure frequency or
`war-t=length_ It comes in sizes rangng from approx-
`imately one tenth die diameter of a hulnm hair to
`the size of a very large building. in powers ranging
`from l{l"'l' to Ill?” "IV, and ill wavelengths ranging
`fromthe microwave to the soft—X-ray spectral regions
`with corresponding frequencies from 10" to ID” Hz.
`Lasers have pulse energies as high as 1D‘ J and pulse
`durations as short as 5 x lll'l5 s. They can easily
`drill holes in the most durable of materials and can
`
`
`
`weld detached retinas within the human eye. They are
`a ltey component of some of our most modern com-
`munication systems and are the "phonograph needle"
`ofour compact disc players. Tl'lI3'y' perfonn heat unat-
`mentnfliigh-sI:rengtlI mateiials. such as die pistons of
`our automobile engines. and provide a special su rgi—
`cal knife for many types of rrtedical procedures. They
`actas targetdesignators for military weapons and pro-
`vide for the rapid che:cl:—out we have oorne to expect
`at the supermarket. What a remarkable range of char-
`acteristics for a device that is in only its fifth decade
`ofciristencel
`
`INTRODUCTION
`
`There is nothing magical about a laser. It can be thought of as just another type
`of light source. It certainly has many unique properties that make it a special light
`sourcc. but these properties can be understood without ltnowledge of sophisticated
`rnallrematical techniques or complex 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 heat 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 understand a specific type of laser system in detail.
`
`DEFlN|'l'lON OF THE LASER
`
`The word laser is an acronym for Light Amplification by Slimulalod Emission of
`Radiation. The laser rlaltes use of processes that increase or amplify light signals
`after those signals l'IEl\-‘E been generated by other means. These processm include
`(I) stimulated emission. a natural affect that was deduced by considerations re-
`lating to lherrnodynarnie equilibrium, and {2} optical feedback {present in most
`
`
`
`
`
`
`
`

`
`INTRODUCTTON
`
`Optical resonator or cavity
`
`Jtmplltyhg rnadlurn
`
`Laser heart:
`
`
`saa\\\$-
`
`
`F|g|.I-o 1-1 Sirnplrlied
`5-clwernatic ottypical laser
`
`Fully retlecting
`nflror
`
`Partlally transmtting
`rrfltor
`
`lasers) that is usually provided by minors. Thus, in its simplest fonn, a laser con-
`sists of a gain or amplifying medium {where stimulated emission occurs}, and a
`set of mirrors to feed the light back into ‘me amp-li:lier for continued growth of the
`developing beam, as seen in Figi.u'e 1-I.
`
`SIM PIJCITY OF A LASER
`
`The simplicity ofa laser can be understood by oonsideri ug the light from a-candle.
`Normally, a burning candle radialcs light in all directions, and therefore illumi-
`nates various objects equally if they are equidistant from ll1e candle. A laser takes
`light that would uorrrially be emitted in all directions, such as from a candle. and
`concentrates that light into a single direction. Thus, iftlte light radiating in all di-
`rections from a candle were concentrated into a single beam of tile dia.tn.eLer of the
`pupil of your eye {approximately 3 mm). and if you were standing a distance of
`l m from the candle. then the light intensity would be I.0lll],{[.‘fl times as bright as
`the light that you normally see radiating from the candle] That is essentially the
`underlying concept of die operation of a laser. However. acandle is not the lrind of
`medium that produces ainplificalion. and thus there are no candle lasers. ll talces
`relatively special conditions within the laser medium for amplification to occur,
`but it is that capability of talring light that would normally radiate from a source in
`all directions — and concentrating that light into a beam traveling in a single direc-
`tion— that is imrolved in making a laser. These special conditions. and the media
`within which they are produced. will be described in some detail in this book.
`
`UNICI-l.FE PROPERTIES OF A LASER
`
`The beam of light generated by a typical laser can have many properties that are
`unique. When comparing laser properties to those of other light sources, it can
`be readily recognized that the values of various parameters for laser light ther
`greatly exceed or are much more restrictive than ll1e values for many common
`light sources. We never use Easels for street illumination, or for illumination within
`our houses. We don't use I:l'JE.tI1 for searchlights or flashlights or as headlights in
`
`
`
`
`
`
`
`

`
`INTRODUCTION
`
`our ears. Lasers genersfly have a narrower 1'reqrrenr:}' distri bution. or much higher
`inlerrsity, or a much greater degree of oollimation. or much shorter pulse duration.
`than that arraiiable from more common types of light sources. TI'rerefor'e. we do use
`them in oompacl disc plagrers. in supemlarket check-out scanners, in sunrejfing in-
`slnrmnnta. nnrl in 1'ru=-.rI'r:aI appiinnlinns as rr srrrginnl knife rrr far welrli I13 I'iE'.IHI'.‘i'IE'rt'i
`retinas. We also use IJre1'n in communications systems and in radar and rnililary
`targeting appliealions, as well as many olher areas. A [user i.-: r] speciaffied light
`source that sirorrtd be used o.er_1.' when irrr rrrsiqrre pmpenier are required.
`
`THE LASER SPECTRUM AND WAVELENGTH5
`
`A portion ofthe eier::tr'oJ:r1ag'ne1ic radiation spectrum is shown in Figure 1-2 for the
`refine covered by ermenlly existing lasers. Such lasers span the wavelerrglh range
`from the far infrared part ofthe spectrum (.3-. = I_C|DD run) to the soft—I—ray region
`[1 = 3 nm). thereby etweri rig a range of wavelengflis of almost six orders ofrnag-
`nitride. There are several types of units Ihal are used to define laser wavelengths.
`These range from mierometersormierons in m] in the infrared to nanometers tnm}
`and angstroms {girl in the visible. ultraviolet {UV}. vaerrrrm aitraviolet (VUV ,1. es-
`Lrerne 1.riT.1'aI.rio1e1 tELTV or XLFV}. and so1'T.—X—ra},I (SXRJ spes:I.ra.l regions.
`
`WAVELENGTH UNITS
`
`lrrnr : I04‘ rn;
`1.5.: 10-“ In;
`lnm :1l]‘9 m.
`
`Consequently. ] n1ierorr[,u.m‘r = lllillflangstronls {fir} = 1.000 nanometers {nm}.
`For example. green iight has a wavelength of S x H} "T m. : 11.5 ram : 5.'|JGUJ5L :
`500 nm.
`
`HF
`
`CO
`
`>59 |.'F
`Diaee
`._ ......-
`Ar
`--
`-|-
`
`Figrru is wmrengrh
`rarge o$VarioLei lasers
`
`I
`1
`. FIFI'I.::.::rr;.
`-u- .
`....-
`
`Hid:-,.'
`N2
`He-Ne
`«rs
`P£d"'r'.irG
`Ho.[,:u
`
`SN-I-Ha;
`1,na;grs
`
`5“?
`
`”*'"‘’‘
`
`i
`
`E"I?."“!“ W1
`Ari:
`Tr:_n.Ia93
`SM! 3|€-P.r'.r5I=
`Lrlflmrrralel
`"r'i:d:r$u
`Inlrared
`Far lrrfrared
`:..... j._'.j_'_a. 4... __L_..._T‘: ____.
`Bflpm
`roqrm
`3pm
`1ym an-Elnm 10IJnrn
`3tJnm ttlrrm
`+
`It :
`
`——-- ENERGY - ..
`
`
`
`
`
`
`
`

`
`INTRODUCTION
`
`WAVELENGTH REGIONS
`
`Far infrared: ID to I.0GD ,-.r.m'_.
`middle infrared: I to IE] ,rr.m‘,
`nearinfrared: 0.? to l.jlI'llf.
`visible: {L4 to 0.7 rim. or 4-00 to T00 nm:_
`ultraviolet: 13.2 to [L4 ,um_, or 200 to dflfl nm;
`vacurrrn ultraviolet: 0.] to 0.2 urn. or 1043 to 21]] nm:_
`c:IttneIne ultraviolet:
`ID to 100 nmj.
`soft X-rays:
`I nor to approximatelgr 20-30 rrm [some ovedap with EUV}.
`
`A BRIEF HISTORY OF THE LASER
`
`Charles Townes tool: advarlage of the stirrurlated emission process to oonsutrct a
`microwave amplifrer, referred to as a rrrxrser. This device produced a coherent beam
`of microwaves to be used for communications. The frrst 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 tire dirnensions of the device. so extrapolation to the optical regime — where
`wavelengths were five orders of magnitude smaller— was not an obvious extension
`of that work.
`
`In I958, Townes and Schawlow published a paper conoeming theirideas about
`extending the rnaser concept to optical frequencies. They developed the concept
`of an optical arnpiifier sunorrndcd by an optical mirror resonant cavity to allow for
`growth of the beam. Townes and Schawlow each received a Nobel Prize for his
`wot}: in this field.
`
`In I960, Theodore It-{a;man of Hughes Research Laboratories produced the
`frrst laser using arrrby crystal as the amplifier and aflashlamp as the energy source.
`The helical Hashiarnp surrounded a rod-shaped ruby crystal, ar1d the optical cavity
`was formed by coating the flattened ends of the ruby red with a highly reflecting
`material. An intense red beam was observed to emerge from the end oftire rod
`when the Elashlamp was tired!
`Tire :Frrst gas laser was developed in I96I by A. Javan, W. Bennett. a.rrd D. Har-
`riott of Bell Laboratories. using a mixture of helium and neon gases. At the same
`laboratories. L. F. Johnson and K. Nassau demonstrated the first neodymium laser,
`whichirassince become oneofthe most reliable lasers available. Tlriswas followed
`
`in 1963 by the first serrricorrdoctor laser. demonstrated by R. Hall at the General
`Electric Research Laboratories. In I963. C. K. N. Patel of Bell Laboratories dis-
`covered the infrared carbon diortide laser. which is one of the most efficierrt and
`powerful lasers available today. Later: that same year. E. Bell of Spectra Physics
`discovered the first ion laser. in rrrercrrry vapor. In 1964 W. Bridges of Hughes Re,-
`search Laboralories discovered the argon ion laser, and in I966 W. Silfvast. G. R.
`Forvies, and B. D. Hopkins prodtrced lire Iirst blue heliun'r—cadrnir.rm metal vapor
`
`
`
`
`
`
`
`

`
`INTRODUCTION
`
`laser. During that same year. P. P. Sore-Irin and I. R. Lankard of the IBM Research
`Laboratories developed the Iirst liquid laser using an organic dyedissolvcd in a sol-
`vent. thereby leading to the category of broadly tunable lasers. Also at that tin1e.
`W. Waiter and on-workers at TRG reported the first copper vapor laser.
`The first vacuum ultraviolet laser was reported to occur in molecular hydro-
`gen by R. l-Iodgson of [HM and independently by R. Waynant eta]. of the Naval
`Research Laboratories in 19'i'D. The first of the well-lrriown rare-gas—halide es-
`cimer lasers was observed in xenon fluoride by J. J. Ewing and C. Brat: of the
`Ftvco—Everett Research Laboratory in l9'?S.
`[n that same year. the tits: qi.ianti.im-
`well laser was made in a gallium arsenide semiconductor by J. van der Ziel arid
`co-worlters at Bell Laboratories. In 1".-'I'.I'-IS. J. M. I. Madey and co-workers at Stan-
`ford University demonstrated the lirst free-electron laser amplifier operating in the
`infrared at the CD3 laser wavelength. In I979. Wailing and co-workers atfitllied
`Chemical Corporation obtained broadly tunable Iaser oiitptn fnoma solid-state laser
`material called alexaridrite. and in I985 the first sott—I—ray laser was successfully
`demonstrated in a highiy ionized selenium plasmaby D. Matthews and a largeni.rrn-
`ber of co-worlaers at the Lawrence Livermore Laborazories.
`[it 1936, F‘.
`llr1Dt.tl.T.Dl‘|.
`discovered the titanium sapphire laser. In I991, M. Hasse and eo—workers devel-
`oped the first blue -green diode laser in Znfle. In I994. F. Capasso and co-workers
`developed t.he qi.tEt.I't.1.1.tI'I1 cascade laser. In I995. S. Nahamura developed the first
`blue diode laser in Ga.NJ:aased materials.
`In l96l, Fox and Li described the existence of resonant transverse modes in
`
`a laser cavity. That s