LASER FUNDAMENTALS
`
`SECOND EDITION
`
`WILLIAM T. SILFVAST
`
`Schooi 0‘! Optics ICRECIL
`University of Central Fiorida
`
`
`
`CAMBRIDGE
`UNIVERSITY PRESS
`
`i
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`Hzewfillen pmmminn nfflamhtjdge University Press.
`
`First ptlblished 2004
`
`Printed in ma United Slants of Amerllcn
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`Sllfvast. 'W'III‘ia1:I1 T'I1.ou:1a5. 1937-
`Laaeriurudansemals F"PrTIlia.m T. Silfvasl. — 2nd ed.
`p.
`cm.
`Includes b':tIIiogn1_uhi::a.! ref-c'mnmsm1.d influx.
`[SEN CI-3'2]-E3345-1]
`I. Lasari.
`I. ‘fills.
`
`ZR}-1
`TJLID-'.I'5.S52
`ISfl_3lS"&— I:I|:"l1
`
`ISBN fill E33-15 III hardback
`
`1003055131
`
`ii
`
`

`
`Contents
`
`Preface lo the Second Edirion
`
`Prefare to the Firs‘? Edition
`
`.-I.rknmr.I'edgmem5
`
`1
`
`INTHEIJLICTI-ON
`OVERVIEW
`lntnmduciion
`Deiiuilion of the Laser
`
`SimpI.iI::il'_1.' til’ a Laser
`l'niqu>e Properties of :1 Lu.-oer
`The Laser Spectrum and ‘|r"r'aveIu31glIIs
`A Brief I-]islor'_|' uflhe Laser
`Ifh'en"iew of the fluolt
`
`SECTION 1 . FUNDAMENTAL WAVE PROPERTIES OF LIGHT
`
`2 WAVE NATURE OF LIGHT —THE INTERACTION «OF LIGHT
`WITH M.ATER7IflII.5
`D-'Ir'EIl‘|I']'E'W
`
`2.1 -.‘t'1aJtweII’s I-Zquatiuiis
`2.1 I't'Ia11w.-I‘I’s ‘I-'c'a1-‘e Equations
`MaJ:weII‘5 Wave Equations for :5 Vacuum
`Solution oI'II]':o General Wave Equation — Equivaltznoe of Light and
`Electromagnetic Radiation
`Wave ‘Velocity — Phase and Group Veioccilies
`Gornemlizod Solution of the Wan: Equation
`Tra.11s\«'erse' Electromagnetic Waves and PoIa:I'ii:Ed Light
`Flow oI'E!ocu'on1.agn+:t'ic Energy
`Radiatlon from a Point Source fEII:cu'it' Dipole Rodi ation}
`2.3 Interuclinn of Eleclromugueiit Radiation I Lighlr with Mailer
`Speal of Light in :1 Mcdium
`Maxwell's Equations in a Medium
`Applicaljon of Maxwell's Equations to Diolecuic Matedals —
`La:.I::r Gain Media
`
`Complex I.lIIEI.l-23! of Refraction — Optical Constants
`Absorption and Dispersion
`
`page xix
`ui
`
`uiii
`
`
`
`E516-1D‘-C1'JI-B-L.nJt\JI'..l————
`
`I-J-J-J-JIM.)-——'_u'II\-3"-‘$--.ILnI
`
`23
`24
`
`2‘?
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`vii
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`

`
`viii
`
`CONTENTS
`
`3&1
`315
`37
`3 El-
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`39
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`43
`43
`45
`-1:}
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`49
`5 I
`54
`S4
`54
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`57
`5 1'
`59
`
`I53
`
`6'?’
`6'?
`fili-
`
`TU
`T0
`TI
`TI‘ 2
`
`Estimating Particle Densities of Materials for Use in the
`Dispersion Equafions
`1.4 Coherence
`
`Temporal Coherence
`Spatial Coherence
`REFERENCES
`I'IDl1LEJtlS
`
`SECTION 2. FUNDAMENTAL GJAHTUM PROPERTIES BF LIGHT
`3 PARTICLE NATURE OF LIGHT — DISCRETE ENERGY LEVELS
`D"t'ER'It'IE'W
`
`J-.I Bohr Theory ol‘th4.- I-lydrogen Art‘-om
`Historical Development of the Concept of Discrete Energy Levels
`Energy levels of the Hydrogen Atom
`Frequency and Wauelengili oi‘ Emission Lines
`Ionization Energies and Energy LE3".-‘HIS oflons
`Photons
`
`32 Quantum Theory of Atomic Fitergy I.c't'-Els
`Wave Nature of Particles
`
`Heisenberg Unoonainty Principle
`Wave Theory
`Wave FuncI.ion_s
`Quantum States
`'l11e Schrodingerwavc Equation
`Energy and Wave Function for the Ground State of the
`Hydrogen Atom
`Excited States of Hydrogen
`Aflowed Quantum Numbers for Hydrogen Atom Wave Functions
`J3 Angular '.'t'1onIoI1I1r.rIIi of Atnnts
`Orbital Angular Momentum
`Spin Angular Mtnnenlzurn
`Total Angular Momenuim
`J21 Eltergy I..L-vols Associated with Doc-Electnin A toms
`fine Slzrtuzhtre o-f Speuctral Lines
`Pauli Exclusion Principle
`J-.5 PI£I'l'ltl2IlI'.' Table oi'tJIt- Eiements
`
`Quantum Conditions Associated 'W'lI2ll Multiple Electrons Attached
`to Nuclei
`
`Shorthand Notation [or Electronic Configurations of Atoms Having
`More Than Dne Electron
`
`J-.6 EnH'g_I.' Lew.-l.sot‘|.'tIt|lti-FJectrnn .-ittoms
`Energy-—Lewcl Designation for IL'l1.Ilti—ElcoI.ron States
`R:.1.<.sell—Sa.urI=der5 or L3 Coupling — Notation for Energy Levels
`Energy Levels Associated with Two Electrons in Unfilled Shells
`Rules for Obtaining S, L. and J for L3 Coupling
`Degenerucy and Staosdcal Weights
`j—j Coupling
`Isoelectrortic Sealing
`
`

`
`C'DNTHtl'l‘S
`
`REFERENCES
`PROBLEMS
`
`4 RADMTNE TR ANSIT IEINS AMI} EMISSION LINEWIDTH
`D'l:'E.R‘lr']E'lHn'
`
`-11.1 Decay ol'Excited States
`Radiative Decay of Excited States of Isolated Atoms —
`Spornaneo as Emission
`Spontaneous Ernission Decay Rate — Radiative Transition
`Probability
`Li leti me of a Radiating Electron — Tl1e Electron as a Classical
`Radiating Harmonie Dscillator
`Nonradiative Decay oi the Excited States — Collinnnal Decay
`-1.1 Emission Emaiieiiing and Linewidtlt Due to Raifrative Decay
`Classical Emission Linewidtli of a Radiating Electron
`Natural Emission Linev.'idtl'L as Dedtteed by Quantum Nlochnnics
`(Minimum Linewidtli}
`4..'- Addifiolul Enlisfioil-Broadening PI'wee-sses
`Broadening Due to N'onradistive{E'ollisiona1l Decay
`Broadening Due to Dephasing Collisions
`Atmorphodis Crystal Broadening
`Doppler Broslzlening in Gases
`Voigt Linesltagie Profile
`Broadening in Gases Due to Isotope Shifts
`Comparison of‘-lafious Types o1'Emission Broadening
`-I.-l Quantum Wleelianietil Description of Risdiating Atnins
`Electric Dipole Radiation
`Electric Dipole Matrix Element
`Electric Dipole Transition Probability
`Oscillator Strength
`Selection Rules for Electric Dipole Transitions Involving Atoms
`with a Single Electron in an Unfilled Subsbel!
`Selection Rules for Radiative Transitions Involving Atorrts will‘:
`More Thai: One Electron in an Unfilled Sulirsliell
`
`Parity Selection Rule
`lnelficient Radiative Transitions — Electric Quadrnpole and I3-flier
`Higher-Cinder Transi tions
`REFERENCES
`FRBBLEMS
`
`5 ENERGY LEVELS AND RADIATNE PROPERTIES OF MOLECULES.
`LIQUIDS. AND SCILIDS
`D"r'E.ll‘.‘lI'lE."llI'
`
`5.1 ilrlelecular Energy ‘Levels and l-ipLecI.r".1
`Energy Levels of Molecules
`Classification oi" Simple Molecules
`Rotational Energy Le.vels of Linear Molecules
`Rotational Energy Levels of Symrnetrie—Top Molecules
`Selection Rules for Rotational Transitions
`
`815
`36
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`89
`39
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`9|]
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`91]
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`94
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`95
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`130
`
`131
`131
`13!
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`135
`135
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`135
`135
`138
`I39
`1-fl-I
`1:1-I
`
`

`
`EDHTEHT5
`
`‘Vibrational Energy Levels
`Soletnion Rule For '1.-"ibrational Transitions
`P.otational—"tu"ibrational Transitions
`Probal:-itities of Rotational and Wbrafionai Transitions
`
`Electronic Energy Let-'cl.s of Mo locales
`Electronic Transitions and Associated Selection Rules of
`Molecules
`Emission Lirtewidth of Molecular Transiuons
`
`The Franclt—Condon Principle
`E:tcirn.er Energy Levels
`5.2 Liquiti Energy L-l."t'i£'I5 and Their Radiation Proipei1:ies
`Structurc of Dye Molecules
`Energy Levels of Dye Molmulcs
`Excitation and EJTtlSSl|'_1-I1 of Dye Molecules
`Drrtrirnental Triplet States ofDye liiolocules
`5.3 Fatergy Let-'e!s in Solids — Dielectric Laser llr'l:IIeri.als
`Host Materials
`
`Laser Species — Dopant Ions
`i"la.rTou.'-Linewirlth Laser Materials
`Broadband Tunable Laser Materials
`
`flroaclcrting Mechanism for Solid-State Lasers
`5.4 F.nerg:I.' Levels in .‘-iolids — Semicond trctor Laser Matefiais
`Energy Bands in Crystalline Solids
`Energy Levels in Periodic Structures
`Energy i_.E.‘t'ElS ol'Coi1t:lucto1:s. Insulators. and Semiconductors
`Excitation and Decay of Excited Eilergy Levels — Recombination
`Radiation
`
`Direcl and Indirect Eandgap Se:I11i.conductors
`Electron Distribution Function and Density of States in
`Sernicootluctors
`lntri nsic Semiconductor Materials
`
`Extrinsic Semiconductor Materials — Doping
`|:I—n Junctions — Recombination Radiation Due to Electrical
`Excitati on
`
`Heterojuoction Semiconductor Materials
`Quantum ‘Wells
`Variation offlaridgap Energy and Radiation ‘Wavelength with
`Alloy Composition
`Recombination Radiati on Transition Probability and Linewidlli
`nsrcnnnces
`enonte.-its
`
`o RADIATION AND ‘I1-IERMAL EQUILIBRIUM — ABSORPTION AND
`STIMULAIED Eltl|55lC|N
`ovetwlszw
`
`6.1 Equililtriuni
`Thertnal Equilibrium
`Thermal Equilibrium via Conduction and Convection
`Thermal Equilibrium via Radiation
`
`143
`143-
`144
`145
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`149
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`
`

`
`CJDHTEIIITS
`
`til Radiating Bodies
`SLelan—-Boltzmann Law
`Wien's Law
`Irralzlience and Radiance
`
`ti._1 Cavity Iladiatiim
`Con nling the Number of Cavity Modes
`Ra_I,rleigh—Jeans Formula
`Planck’: Law for C91.-'It'_'f Radiation
`Relationship between Cavity Radiation and B-Iaokbody
`Radiation
`
`Wavelength Dependence of E'IaokF:Iodg..' Ernissi on
`6.4 fithszoriiiinn and Stimulated Emiflion
`The Ptineiple of Detailed Balance
`A.bso1:'pIion and Stimulated Ernission Ce-eifieients
`REFEREE EES
`|'|1onr.E:.1s
`
`SECTION 3. LASER MIIPLIFIERS
`
`? CONDITIONS FOR PRODUCING A LASER — POPULATION
`INVERSIOHS. GAIN. AND GAIN SATURATION
`l}'I:'E'IIJI'IE‘H'
`
`"M Absorption and Cain
`Absorption and Gain on a Homogeneouely Broadenetl Radiative
`Transition [Ln-rentzian Frequency Disuibution}
`Gain Coefiioient and Stimulated Emission Cross Section for
`
`Homogeneous Broadening
`Absorption and Gain on an Inhomogeneously Broadened Radiative
`Traneiti on [Doppler Broadening wit]: a Gaussian DIttl.|!'IlZ||.tI.I on?
`Gain Coefiieient and Sti mulaied Emission Cross Sedion for
`
`Doppler Broadening
`Statistical ‘Weights and the Gain Equation
`Relationship of Gain Coelficient and Stimulated Emission
`Cross Section to fltbsorplion Coeflieieni and Absorption
`Cross Section
`
`.2 Population Inversion tI"«'I.'1:easa1jr Condition For :1 Laser!
`TJ ls"-oturittion Intensity tfinflici-i.-nl Condition for a Laser}
`14 Development and Growth of a Laser Beam
`Growth of Beam for a Gain It-'le::liuni 1.!.'iI:l1 Homogeneous
`Broadening
`Shape or G+.'.‘.'UTt'IDll'}" of Amplifying Medium
`Growth of B-earn for Doppler Broadening
`'l'.5 Expunen-tial Growth Footer tflazin]
`]".t'§ Thnsholtl Requirenients tier :1 Laser
`Laser with No Nlirrors
`Laser with One Mirror
`Later with Two Mirrors
`Il£E.l'EREN£‘E.‘.i
`FIGBLEMS
`
`EDI
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`EDS
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`
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`EDS
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`133
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`233
`24I
`244
`145
`24?
`247
`2415
`249
`253
`253
`
`

`
`xii
`
`CONTENTS
`
`LASER OS-CILLATICIN ABOVE THRESHOLD
`DVERVIEW
`3.1 Laser Gain Saturation
`
`Rate Equations of the Laser Levels That loclude Stimulated
`Emission
`
`Population Densities CI-T Upper and Lower Laser Levels with
`Beam Present
`
`E-rrI.aEI-Signal Gain Coefficient
`Saturation of the Laser Gain above Threshold
`
`3.1 Laser Beam Gmwtli beyond the Saturation lnteslsilp
`Change from Ex ponentisl Growth to Linear Growth
`Steady-State Laser Intensity
`3.3 Optimization r.II'L1s»er Output Power
`-Dptimurn Output -.'t-!in'or Transmission
`Dptimurn Laser Output Intensity
`Estimating Dptirnurn Laser Dutpot Power
`3.4 F.nerg'_v Exchange between Upper I.aser Level Population and
`Laser Photons
`Decay Time ofa Laser Beam within an Optical Cavit_v
`Basie Laser Cavity Rate Equations
`Steady-S tate Solutions Izlelow Laser Threshold
`Steady-S Late Elperation above Laser Threshold
`E5 [..aser Output Fluctuations
`Laser S-pflring
`Relaxation Oscillations
`
`HI: Laser It mplilieis
`Basie Arnplilier Uses
`Propagation ofa High-Power. Short-Duration Gplicai Pom through
`an Ampli fier
`Saturation Energy Fluenee
`Amplifying Long Laser Pulses
`Amplifying Svhort Laser Pulses
`Comparison of Effleieru Laser Anipliti ers Based upon Fundamental
`Saturation Limits
`
`It-'iin'or Array and Ronator {Regenerative} Amplifiers
`IIEFERENEI-".5
`PRDELEMS
`
`REQUIREMENTS FOR OBTAINING POPULATION INVERSIONS
`D'\"ER'la"IE'W
`
`inversions an-rl Two-Level Syflems
`9.l
`.2 Relative [Ieeay Rates — Radiative versus Collisional
`9.} Steady‘-Stale I:I1versions in TIIree- and Four-l_.eveI 5:|.'S‘IIE‘l'I.'l5
`Tnree-Level Laser with die Intennediale Level as the Upper Laser
`Level
`
`Tl'Lree-Level Laser wifli Hie Upper Laser Level as the Highest Level
`Four—Level Laser
`
`9.4 Transient Pn§pu.I:11ion Imrersinns
`
`255
`255
`255
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`256
`25?
`252
`258.
`258
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`235
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`283
`233
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`290
`290
`290
`292
`293
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`295
`298-
`3!]!
`364
`
`

`
`CEXETENTS
`
`xiii
`
`9.5 Pmcesse-5 That Inhibit or Destmy inversions
`Radiation Trapping in J1‘tton'I.s and Ions
`Electron Collisionnl Thermatizaticai of the Laser Levels in Atoms
`and Ions
`
`Comparison of Radiation Trapping and Electron Collisi-onal Mixing
`in a Gas Laser
`
`Ahsorpn on ‘W'li]'lll'I the Gain Medium
`REFERENCES
`Pllflfl-l.EllrIS
`10 LASEFI PUMPING REQUIREMENTS AND TECHNIQUES
`Cl‘lr"EJl'l-"IIi.'HI'
`
`lll.1 I.-Excitation or Pumping Threshold Requirements
`Ill.1 Pumping Patlrvt-'n].'s
`Excitation by Direcl Pumping
`Excitation by Indirect Pumping [Pump and Transfer:
`Specific Pump-and-Transfer Processes
`Il}..'i- Specific Excitation Paranseters .JLsso-ciated with
`Optical Pumping
`Pumping Geometnet
`Pumping Requirements
`A Sirnplilied Optical Pumping Approximation
`Trariwerse Pumping
`End Pumping
`Diode Pumping of Solid—Sr.a1e Lasers
`C11a.Iaolerir.a1ion tifa Laser Gain Medium with Optical Pumping
`tSlope Efficicncyl
`ll}.-1 Specific Excitation Paraanelsers Assn-cialed with
`Particle Pumping
`Electron Collisional Pumping
`Heavy Particle Pumping
`A More Accurate Description of Electron Excitation Rate to :1
`Specific Energy Level in a Gas Discharge
`Electrical Pumping of Semiconductors
`assert ENCES
`PRODI. EMS
`
`EECTICIN -I. LASER RESD'N.IltTD1lS
`
`11 LASER CJWITY MODES
`G\'Eit\"lEW
`I].1 lntmduflion
`
`11.1 Longitudinal Laser Carit-_I.' Modes
`Fa'|::r_',-—Pe:tol Resonator
`Fabr_',I—Perot ['avI'tj.' Modes
`Longitudinal Laser Cavity Modes
`Longitudinal Mode Number
`Req Ltiremenm for the Development of Longitudinal
`L.-ascr Modes
`
`340'?‘
`3-DE
`
`31 I
`
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`
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`
`382
`
`

`
`xiv
`
`CONTENTS
`
`11.3 Tr'.1.ns'rerse Last.-r Ca1.'it}' Modes
`Fres:ne1—K.irehhofl' Diffraction Integral FDITI1LEiB
`Development of Trmisverfie Modes in a Ca\"it_1.r with Plane-Parallel
`Mirrors
`
`‘J2
`
`Transverse Modes Using Curved Mirrors
`Transverse Mode Spatial Disuibutiens
`Transverse Mode Frequencies
`Gaussian-Shaped Transverse Modes within and beyond the
`Laser Cavity
`1 1.4 Properties of Laser Modes
`Mode Characteristics
`Efl'eet ol Modes en die Gain Medium Profile
`REFERENCES
`PRDBLEMS
`STABLE LESER RESrDflA‘.|'|I}RS AND GAUSSIAN BEAMS
`{!'I'Ell‘1|'IIE"H'
`12.1 Siabclr Cu'n'ed Mirror Cavities
`Cur-I.-wee‘ Minor C‘:-wilies
`ABCD Matrices
`
`Cavity Stability Criteria
`12.2 Pmperlies of Cfllflfiiafl Beams
`Propagation ofa Gaussian Ream
`Gaussian Beam Properties oI'Ts.-‘n-Minor Laser {'a1.'iLies
`Prop-enies of Specific T'wo-Minor Laser Cavities
`Mode Volume ofa ]-lermite—Gaussiart Mode
`
`11.3 Fmperlies of Real Laser l-'I-i.-*.m:|s
`.11.-I Pmpsrgjafion oil’ Gaussian ll‘-earns l-"sing JIBCD Mattriu:-as —
`Corrtplex Beale Phrameier
`Complex Beam Parameter Applied to a TWD—MlHDT Laser Cavity
`REPERENCFE
`PROBLEMS
`
`13 SPECIAL LASER EAVITIES AND C.A‘|flT‘l' EFFECTS
`l}"l'ER‘l'IE'|'l'
`13.1 Unstable Resom11dr:rs
`
`13.2 Q-Switching
`General Description
`Theory
`Methods of Producing Q-Switc'hing within a Laser Cavity
`13.1 Cain-Switching
`13.-I llrlode-I..odiiI1g
`General Deseiiption
`Theory
`Techniques for Producing !I."lode-Locking
`13.5 Puise Slmrtening Tl3I.‘liJl.ll.|IlE'S
`Self—P‘l1.sse Modulation
`
`Pulse Shortening or Lenglzhening Using Group ‘i-'elor:i1g,' Dispersion
`Pulse Compression I|'Sl:t-:::«r-:e.ai.ng} with Gratings -or Prisms
`L||'I.rssl1ort-Pulse Laser and Amplifer System
`
`384
`385
`
`3315
`39D
`39!
`392
`
`393
`396
`39¢’:
`39?
`399
`399
`4-02
`-103
`4'-1-[I2
`452
`
`4-10
`:1]!
`4-12
`41?
`42!
`423
`
`425
`-123
`43 2
`4-3 2
`43-1
`434
`434
`439
`439
`4-41
`
`451]
`4-5 !
`45 I
`45 1
`456
`4-62
`
`465
`46?
`
`

`
`CONTENTS
`
`‘IV
`
`13.6 Ring Last-rs
`Monolidlic Unidincclional Single-Mode Nd:‘I'AG Ring Laser
`Two—!'I.-'Iirr::Ir Ring Lasor
`13.7 Conpltx Bi.-am Parameter AnaI'_i'si.-s. .-‘ltpplied to II-Iulli-Mirmr
`Laser Cnfilies
`
`Tnrci:-Mirror Ring Laser Cavity
`TI1rcc— or Fu-ur—Min'or Focttaod Cavity
`13.8 Cavities for I'md1.n:1'ng Spectral Hamming cf
`l.a=.»t=r flulpnl
`Cavity with Additional FaIJl'}'—I3'I3IDII Ettdon for Narrow-Freqoenqr
`Selection
`
`Tunable C'a1."i Ly
`Broadband Tunable cw Ring Lasers
`Tunable Cavity for Ultranarrow-Frequency’ Output
`Distributed Feedback I.‘DFB‘] Lasers
`Distributed Bragg Rcfloction Lasers
`[33 Laser Ifavilies Requiring 5l'I'I:.|I.[-DI“an1E'lE'l' {Iain Regions —
`Asliglnati-tally‘ Compensated Ga!-'itit-5
`l3_ll'I '|.'o':n'I.-gui.r:I-it E'u1.'ilie: For (‘/33 L*.merB
`IIEFERENEFS
`FIIGELEII-IS
`
`SECTION 5. SPECIFIC LASER SYSTEMS
`
`1-II LASER SYSTEMS INVOLVING LOW-DENSITY GAIN MEDIA
`‘.']'h'ER'Ir'][-J'I"
`IILI Atornit: Gas Last.-is
`bitroduction
`H4:liuJ1'i—I"~Ion-11 Laser
`
`General Description
`Laser S1:I1.tt'tLrre
`Excitation Mechanism
`
`Applications
`Argon lon Laser
`Gcncral Description
`Laser Structure
`Excitation Mechanism
`
`Krypton Ion Laser
`Applications
`HeIinm—Cadn1itIm Lastr
`
`General Description
`Laser Structure
`Excitation Mechanism
`
`Applications
`Copper Vapor Lassa‘
`General Description
`Laser Stnicturc
`Excitation Mechanism
`
`Applications
`
`453
`
`4TH
`
`4-'."[I
`4-I'D
`-«I-7'3
`
`4-1'3
`
`4?3
`4-78
`4E[I
`480
`4E|
`484
`
`434
`485
`486
`483
`
`4E'|I
`4EII
`49I
`=‘.I9I
`492
`492
`493
`-194
`49".!‘
`49?
`49?
`498
`499
`509
`5-DI
`SUI
`50!
`502
`304
`505
`
`5-05
`30?
`30-?
`
`

`
`CONTENTS
`
`14.2 Molecular Gas Lassa‘:
`lnlrcrductiun
`Carl:-an Dioxide I.:i5«i.-r
`
`Genera! Desciipfian
`Laser S-lrL:c.1'n1'c
`E‘.U:'i[:I|.iU]1 Mechanism
`
`A.ppI1'c:1lic>n.s
`Eicimer Lasers
`
`GEi'IaE:I'E.i DBscI'ip1iI:I-n
`Lass: SIru.cIu1'n
`Ezcitnliun Mechanism
`
`.n.ppI1'cal.ictn.s
`Nimygau Laser
`Genera! Dcscriplicl-11
`Laser SI.rLLctu1'e and Exciuurion Mechanism
`
`Applicalims
`Far~1n|'ra|neIi G:Is Lasers
`
`Gcimral Dl3S£‘I'i.|J!jDEI
`Lass: S-l1'|.J.I:.‘I]l]'n]
`Excitziliun Mechanism
`
`Applications
`Cheitlicnl Last-rs
`
`Camera! Dnscfipdan
`Laser Slructurc
`Excitalinn Mechanism
`
`Applications
`14.3 K-Ray Plasma Lasers
`Irulmductinn
`
`Pumping Energy‘ Requirements
`Excitalinn Mechanism
`
`Optical Cavities
`}(—Ray Laser Transitions
`A.p-pI:'cal.icIn_=.
`14.4 I-'n:e-Electron 1.3.921‘:
`[nlruducticm
`Laser Struc run:
`
`Applications
`R.IEF"EIi‘.F.‘NE'II.'.S
`
`15 LASER SYSTEMS |NVC|L"d"ING HIGH-DENSITY GAIN MEDIA
`{)\'EIl‘|-'lE‘ll'
`
`15.1 fllgauic D3-'e l.ns:ers
`lnlroduction
`Laser SI.1'L:c1.ur£:
`Excitnlicun M-cc!'I.anisn'L
`
`fitpplicalin-11.5
`15.2 11'-nliIi—SI.:11I: Lasers
`i.|]l.El'JdL|iCEiDfl
`
`SID
`Sell]
`5] I
`5| I
`5 I l
`SIS
`5 I5
`5 I6
`5 I6
`SI’?
`5 I E-
`521]
`521]
`521]
`52!
`522
`522
`522
`523
`523-
`52-1
`524
`524
`524
`524
`525
`525
`525
`525
`SEE-
`532
`532
`532
`535
`535
`5345
`53?
`53?
`
`539
`539
`539
`539
`540
`5-1?-
`5-14
`545
`5-15
`
`

`
`CHITEHTI
`
`Iii
`
`Ruby lulu
`General Dcscriplliun
`Laser 5I1.IcI:.m:
`Ewitnii-an Mechanism
`
`Applicndon:
`NI-nd)& “Hi fldflltn Imus
`General Duuzripiiun
`l..ua' Sltnturc
`Etcituian Huclunism
`
`Applicaiuus
`HmdpiIn~:‘|‘LI" Linen
`General D-::Im‘pt5m
`l.nn:r Sructmv:
`Eu:iInu'm Hnclluixm
`
`Applicnxiixu
`Hen-&yflunI:"t'Ill'hn1 '\'5Inud:Iu1Nd:'1"lr‘ILILnsers
`Gcturllflcicriqrliuo
`Luau: Slmctun:
`Exadlalinn Mmhminm
`
`Appliqmims
`"|"IIu'b|um:\'.A:l.‘- Emmi
`
`Gancrai D|:IcripI.Iun
`Lam Slruulurc
`E:Iu.:i1nI.iun Huclunism
`
`Applications
`Akunthllr limmrr
`
`Gmnml Ducriptilm
`Laser Suuclurc
`Excilntiun Mucbuiun
`
`Applimuium
`Titanium Suppl!!! Lunar
`-Gcnufl Duoriptinn
`Lnmr Shula:
`Exuituinn Hudamism
`Appiuiolu
`(‘Blunts IHAF ad l.lI.'.:|F Luna
`
`Gntuhl [ks-criplirnl
`Lnu:r Stucmm
`Excitlion Mechanism
`
`Applinium
`I-‘In-r Inner:
`
`Gaul! Du-cripliun
`laser Sructnrc
`Enciinli-at: Mnchauiim
`
`Applimaiuu
`III‘-uhr Center lmnsn
`
`G1.-nernlflucripfiun
`Lane: Slrudun:
`
`54?
`54?
`
`549
`
`55!}
`55 I
`553
`554
`555
`555
`556-
`556
`55?
`SF!’
`55'?
`55'?
`553
`553
`559
`559
`
`56!]
`56]
`562
`562
`563
`56-?-
`
`H I
`.5?!
`SH
`5?}
`5?}
`5'1!
`
`

`
`Jnrrli
`
`CONTENTS
`
`Excitation Mechanism
`
`Applications
`15.3 Semiconductor Diode L35-BI‘?
`[ntruducfinn
`
`Four Basic Types of Laser Materials
`Laser Structure
`
`Frrslucncy Control of Laser Dulput
`Quantum Cascade Lascrs
`p-Doped Gennanium Lasers
`Excitation Meci1anisn't
`
`Applications
`REFERENCES
`
`SECl'[Ol'-I ti. FREOLIENCY IHIULTIFLIEATION OF LASER BEANS
`‘I-ti FREQUENCY MULTIFLICATION OF LASERS AND OTHER
`NONLINEAR OPTICAL EFFECTS
`D"t’ER‘|-'II-TIT!‘
`
`"|r‘|"a1'c Pr'o.p:1gal.iIm in an Anisoiruzupi-c Crystal
`'li'§.l.
`16.2 Pularimiirsn Response of}-'Iate{'ia1s to Light
`16.3 Sec-tint!-fllrder hlonlinear Optical Processes
`Second Harrncunic Gclzrsnttic-n
`
`Sttrn. and Diffcrcncc Frequency Gencration
`OptieaJ Pm'a.n1cLric ftscillatiun
`IISJ 'I11ird-flI'der Nonlinear Optical Processes
`Third Harmonic Generation
`
`[nlcnsit}'-Dependcnt Refractive L|'|'LiEtJC — Scl!'—Fcrc1.Ising
`16.5 Nonlinear Optical Materials
`16.6 Phase Matching
`DCSCI'ipliI'.'H1 of]-"hasc Matching
`Achieving Phase Matching
`Types afPJ1a5c Matching
`16.? Snturable Absorption
`16.3 Two-Photon Absorption
`lfi.‘.-I fiirntllated Raman Scattering
`16.10 Harmonic Genenaljon in Gases
`EEFERENCFS
`
`Appendix
`Index
`
`5'34
`S'.I‘I3
`5'3’-ti
`5'?-Ea
`5'.I‘9
`SE!
`SQI
`5'92
`594
`594
`596
`59‘?
`
`El}
`{:15
`filft
`HIT
`ME-
`E19
`GI?
`
`62!
`62+
`
`

`
`1 I
`
`ntroduction
`
`CWEI!Il"IE?'I'|' A laser is a device that amplifies light
`and produces a highly ctirectioual. high-intensity
`bea.n1 that most often has a very pure frequencjr or
`was-'elength.
`It comes in sizes ranging from approx-
`imately one tenth die diaoteter of a human hair to
`the size of a very large building. in powers ranging
`from IEl"° to Ill” W, and in wavelengths ranging
`from the nticrowatre to the sofl—X-ray spectral regions
`witlt corresponding frequencies from Ill“ to ID” Hz.
`Lasers have pulse.eoe:rgies as high as llll J and pulse
`durations as short as i 3-: lll'u‘ s. T'l'te;t' can easily
`drill holes to the most durable of materials and can
`
`
`
`weld detacltcd retinas W'lIl'IlI1 the hLtma.1-eye. They are
`a key component of some of our most modern corn-
`munlcation systccms and an: the "plson-Jgr-tph needle"
`ofeur compact disc players. T'l'tLf,.I perfenu heat treat-
`ment ofhigh-strength nsaterials. such 5 die pistons of
`our autelnobile engines. and pmvide a special surgi-
`cal knife for many types of medical pl'DDECl.ttI'BS.
`'I'I'te'_1.'
`act as targetclesignators for military weapons amiprn-
`vide for the rapid ch.-eck—eut we have come to expect
`at the supermarket. What areroarkable range ofcl1at-
`acteristics for a device that is in only its fifth decade
`of existence!
`
`INTRODUCTION
`
`There is nothing magical about a laser. 11 can be thought ofasjusl another type
`Lrf light sutu me. It LFl.'.1lI‘l.llJ.l}' Iuu litany Lutiqut: §.rurpt.=ILit:.\i tllnt. Iilitkt: it a1 apmsial ligllt
`source. but t:l1ese propesties can be understood vv1'thc-ut knowledge of sophisticated
`matlternarical techniques or cemples. ideas. It is the objective of this test It: explain
`the operation of the Iasex in a simple. logical approach that builds from one con-
`cept to the next as the chapters evolve. The concepts, as they ate 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 tutderstand a specific type of laser system in detail.
`
`DEFINITION OF THE LASER
`
`The word laser is an aeaonym for Light Amplification by Stimulated Emission of
`Radiation. The laser makes use of processes that increase or amplify light signals.
`after those signals have been generated by other means. These processes include
`[I] stimulated emission. a natural effect that was deduced by considerations re-
`lating to lherrnod}-nam-.c equilibrium, and [2] optical feedback Epresent in meat
`
`

`
`I
`
`INTRODUCTION
`
`Up-lical resonator or cavity
` \
`Amplflythg rnedlurn
`
`
`
`LE|flEt' beam
`
`fir-M 1-1 Simplified
`scl'uen1atic oitypical laser
`
`Fully rellecting
`NEHIIF
`
`Parllallytranen-ttlng
`'!1'lfl'Jf
`
`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 mirrors to feed the light back into the amplifier for continued growth of the
`developing beam. as seen in Figure 1-I.
`
`SIM Pl.|ClT‘t' OF A LASER
`
`The simplicity ofa laser can be understood by oonsidcri rig the light from acanrlle.
`Normally, a hunting candle :l'fl.Cliflil{‘.S light in all directions. and therefore illumi-
`nates ‘various objects equally if they are equidistant from the candle. A laser takes
`light that would no-rrnally be emitted in all directions, such as from a candle. and
`concentrates that light into a single direction. Thus. if the light radiating in all di-
`rections from a candle were concentrated lI.'Il:t] a single beam -of the diamietner 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 l.fll}C|_.EHI| times as bright as
`the light that you normally see radiating from the candle! That is essentiaily the
`underlying concept of the operation of a laser. However. a candle 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 of taking light that would normally radiate from a source in
`all directions — and concentrating that light into a beam traveling in asingle 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.
`
`UNIQUE PRGPEETI E5 OF A LASER
`
`The beam of light generated by a typical lasesrcan 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 either
`greatly exceed or are much mom restrictive than the values for many common
`light sources. We never use lasers forstreel illumination, or For illumination within
`our horses.
`‘We don't use Ihen1 for searchlights or flashlights or as headlights in
`
`

`
`lH'I"l!lZlDUCT|DN
`
`our cars. Lasers. generaly have a narrower frequency distribution, or much higher
`intensity. or II much yeater degree of oollimalion. or much shorter pulse duration.
`than that available from more oornmon types of light sources. Tlncrefore. we do use
`them in oompact disc phyers. in supezrmarlcet chock-out scanners, in suneying in-
`struments. and in :|'I'.|:£H2llCE.l applications as a surgical ltrtife or for welding detached
`retinas. We also use thorn in communications systems and in radar and military
`targeting applications, as well as many other uneas. A laser is a specialized light
`some that should be used only when its unique properties are required.
`
`THE LASER SPECTRUM AND WAVEEIIGTHS
`
`A portion of the E:l6ElII'Dl!I1.fi.gI1l3.1.'l.C radiation spectrum is shown in l7Ig1.n'e 1-2 for the
`region cover-rd by ::urrentl}r e.It1'stirIglaseIs_ Such lasers span the wavelength range
`from the far infrared pan ofthe speelznsm l.i'L = I,C|Dfl _u.n1‘] to the soft—X—ray region
`U-. = 3 nm}. thereby ootefing a range of wavelengths of almost six orders of mag-
`nitude. There are several types of units that are used to define laser u-mrelengtlls.
`These range from micrometers ormierons tum] in the infrared to nanometers tom}
`and angstroms {sat} in the visible, ultlavioiet {UV}, vacuum ultraviolet [VUV 3, ex-
`treme ultraviolet tELTTt-' or XUV], and soft—X—ray (SXRI spectral regions.
`
`WAVELENGTH UNFFS
`
`lam : l'fl"E' m;
`1.6. = 10-1“ m;
`1nm:ll]'9 m.
`
`Consequently. I Il'tlCr1'.tl1[,t.LI'nl = IDJDEK} angstroms Lit] = I.DD{}nanometers{I1m].
`Forexasnple. green ligh: has awavelength of 5 Jr: l[I‘7 n1 : [L5 tern : 5.000 tit :
`SDEI mo.
`
`Fifima $2 Wavelength
`range efvarious lasers
`
`HF
`
`CC}
`
`92-22 .199
`
`Ar-u — — -
`
`N2
`Ruby
`KN’
`Ha-‘ta
`M:l"'|‘.fi{3
`Ho..|:|I
`
`I’-|F‘H_::.qrs.
`-u
`.-._.-
`
`Salt!-Herr
`Lasers
`- _.
`..—
`
`‘3°'=
`
`HM“
`
`Far lnlrflred
`
`lrllrured
`
`E’.'M"*°t".
`TI:JI_.Ia93
`"a'isel:nI
`
`AH’-
`Ultrert.-tolet
`
`SH‘. Ill-Pay:
`
`aflp
`
`IEJH1
`
`3pm
`4-
`
`it
`
`10I:Inm Bfirn
`
`HJn_rl1
`
`——- ENERGY ll?) — ..
`
`

`
`INTRODUCTION
`
`‘NAVIELENGTH REGIONS
`
`Far infrared: It] to l.tJCll] ,um'.
`middle infrared; I to It] yam:
`near infrared: 0.7‘ to lptrn;
`visible: 0.4 to l].'i" em. or 4-Dtl to THE! um‘.
`ultraviolet: 0.2 to [L4 is rn, or EDD to 400 nm:
`vacuum ultraviolet: {Ll to 0.1 nm. or 100 to 201] rim:
`ex't.re-me ultraviolet: It] to 101] Elm‘.
`soft X-rays:
`l nm to approximately 20-30 not :some overlap with EUV }.
`
`A BRIEF HISTORY OF THE LASER
`
`Charles Townes took advantage of the stimulated emission process to oonstnrct a
`microwave a.mpl.ifier, referred to as a nxerser. This device produced 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 wavelengd1s produced in the rnnaser were compara-
`ble to the dimensions of the device. so extrapolation to the optical regime — where
`wavelengths were five orders ot'1:r.agnimde sn'J.aller— was not an obvious extension
`of that work.
`
`In I958. Townes and Schawlow published a paperoonoeming theirideas about
`extending the maser concept to optical frequencies. They developed the concept
`of an optical arnplilier surrounded by an optical rnirror1'esonantcavit}- to allow for
`growth oi the beam. Townes ant: Schawlow each received a Nobel Prize for his
`work in this field.
`
`In I966, Theodore Maiman of Hughes Research l_.ah-oratories produced the
`first laser using a ruby crystal as the amplifier and a flashlnmp as the energy source.
`The helical Hashlamp surroundecla rod-shaped ruby eqrstal. and the optical cavity
`was formed by coating the flattened ends of me ruby red with a ligltly reflecting
`material. An intense red bea.m was observed to emerge from the end ofthe rod
`when the fiashlamp was tired!
`The first gas laser was developed in I96] by Pt. Javan, W. Bennett. and D. Har-
`riott of Bell Laboratories. using a n1i.=ttm'e of helium and neon gases. At the same
`laboratories, I... F. Johnson and K..J."~tassau demonstrated the first neodymium laser,
`whichhas since become one of the most reliable lasers available. This was followed
`
`in 19152 by the first semiconductor laser. demonstrated by R. Hall at the General
`E'tectric. Research Laboratories.
`In I963. C. K. N. Patel ofBelI Laboratories dis-
`covered the infrared carbon dioxide Esser. which is one ofthe most eflicient and
`powerful lasers available todav. Later that same year. E. Bell of Spectra Physics
`discovered the first ion laser. in nasrcurv vapor. [:1 1964 ‘W. Bridges of Hughes Re-
`search Laboraiories discovered the argon ion laser, and in I96-6 W. Silfvast. G. R.
`Fowles. and B. D. Hopltins produced the First bloc helinrn—cad1'niurn metal vapor
`
`

`
`INTRODUCTION
`
`laser. During that same year. P. P. Sorolrin and J. R. Lanlurrd of the EM Research
`Laboratories developed the lirst. liquid laser using an organic dyedissolvcd in a sol-
`vent. l.‘l1Bt'E.‘,lJ-)1‘ leading to the category of broadly tunable lasers. Also at that time._
`W. Walter and oo-worlcers at TRG reported the lirst copper vapor laser.
`The tirst vacuum ultraviolet laser was reported to ooeur in molecular hydro-
`gen by R. I-Iodgson of IBM and independently by R. Wavnant et al. of the Naval
`Research l_.ab-orateries i.11 19'i"l]. The first of t.he well-Irnowii rare-gas—l'ral.idc es-
`cimer lasers was observed in Jtenon fluoride by I. J. Ewing and C. Brae of t.he
`Avco—Everet1. Research 1a.bo1ator'_v in I975. In that same year. the Iirst quantum-
`well laser was made in a gallium arsenide semiconductor by J. van der Zlel and
`co-workers at Bell Laboratories. In 1976. J. M. .T. Madey and co-workers at Stan-
`fortl University demonstrated the lirst free-electron laser a.rnp-lifter operating in the
`infrared at the CD3 laser wavelength. In I979. Walling and co-workers at.-ltllied
`Chemical Corporation obtained bmadly tunable laser output frvoma solid-state laser
`material called alexandrite. and in I985 tlie lirst solt—X—ra5t laser was successfully
`denionstratod in a highly ionized selenium plasma by D. Ma1t'rrewsa.ndala1'genum-
`ber of co-workers at the Lawrenoe Liv-ermore Laboratories. In 1936. F‘. Moulton
`
`discovered ‘die titanium sapphire laser. In I991. M. Hasse and eo—worl<ers devel-
`oped the first blue -green diode laser in Znfle. In I994. F. Capasso and co-worIa:en;
`developed the tI|LtEtt't'|‘.I.Et1t cascade laser. In I996. S. I‘-lalramura dev