LASER FUNDAMENTALS
`
`SECOND EDITION
`
`WILLIAM T. SI LFVAST
`
`Sclmol all Opfics J’ CRECIL
`Lhivenily of Central Florida
`
`4:] CAMBRIDGE
`@155: UNIVERSITY PRESS
`
`
`
`
`
`
`
`
`ASML 1109
`
`ASML 1109
`
`

`

`PUBLISHED BY THE PIE STN'DEalTE OF THE. UNIVERSITY DFCAHBBJIIIE
`The P‘il Hiking, 'Ihupinghn Slnael. club-mum Kim
`
`CIIIIBIIIIIE UNIVERSITY PI“
`mmwmmmmyu
`mmmmmmxmr lll]ll-+2Il.lJSA
`4nmumnmm.mnmmwcm,m
`mam-13. 281]I4Ilnd1id.5pnin
`Duclmmmwul,flqr1hwnmsqnhflflm
`twill-I'm“:
`
`Humming
`Wlm.mm
`
`filstaitimflCalllidlelimsijPrms
`Smuladiinnfl‘ifiliamls‘ilfiafim
`
`'l‘llisbnntisinmmlrfll. mummm
`mflnptwfinlfid'nbnumflauimlhafingm
`mmpuduinnd’ugrpxnaymflmm
`mmmdfinmmymm
`
`mammal):
`
`Whmummam
`
`[was-1m mus mdhuafr WILLIS-TE!
`
`|FH]
`
`Am: mufirmmmmmmmmmmmy.
`
`mgcmumnmmmxmm
`Silfru,W|Iim'Ihrm_lm—
`meuflmlsl'lflfiflilnT.filfnst.—2Ifled
`p. m.
`IMWmm illal.
`ISBN fl—SZl—Ell-IS—O
`l. [m 1. This.
`
`TAI675.552 21m
`6335"6 — {Ell
`
`ISBNIIISlIfiBII-SI] hum
`
`3130553252
`
`
`
`
`
`
`
`

`

`Contents
`
`Pmfice to the Second Eiition
`
`Profit: to the First Edition
`
`Acknowledgttents
`
`1
`
`INTRODUCTION
`(WEIWIEW
`Introduction
`Def-filial] of lhe Laser
`
`Simplicily ol' 2 Laser
`Unitpe Properl'les of :I Laser
`The Laser Spectrum and “ravelengths
`A Brief History orlhe Laser
`{fret-fie“ of the Buolt
`
`SECTION 1- FUNDAMENTAL WAVE PROPERTIES OF LIGHT
`
`2 WAVE NATURE OF LIGHT — THE INTERACTION CIF LIJGHT
`WITH MATERIALS
`mum
`
`2.1 Maxwell's Fanatical:
`2.2 Maxwell's Wave Equations
`Maxwell's Wavc Equations for a Vacuum
`Solution of that General 1Wave Equation — Equivalcocc of Light and
`Electromagnetic Radiation
`Wavc Velocity — Phase. and Group Velocities
`Generalized Solution ot'dthWavc Equation
`Ttansvctsc Eloctrotoagoctic Waves and. Polarizotl light
`Flow of Elcctromagnctic lining}.r
`Radiation from a Point Source (Electric Dipole Radiation]
`2.3 [ntenttlioo of Hectronaglulic Radial'lm (light) will Matter
`Spread of Light in a Medium
`Maxwell's Equations in a Medium
`Application of Maxwell's Equations In Diciocu'ic Materials —
`laser Gain Modia
`
`Compic': Index of Extinction — Optical Constants
`Absorption and Dispersion
`
`page xix
`
`ui
`
`xxiii
`
`I
`I
`I
`I
`
`2
`2
`3
`4
`5
`
`9
`9
`
`9
`t2
`[2
`
`13
`17
`2|]
`2]
`2|
`22
`23
`23
`24
`
`25
`
`23
`2.9
`
`
`
`
`
`
`
`

`

`(“TENTS
`
`Estimating Particle Densities ofMaterials {or Use in the
`Dispersion Equations
`LII Coherenre
`
`Temporal Coherence
`Spatial Coherence
`IEFEIENCIE
`[HELENE
`
`SECTION 2. FUHDAHENTAL QUANTUM PROPERTIES OF LISHT
`
`3 “ARTICLE NATURE OF LIGHT — DISCRETE ENERGY LEVELS
`OVERVIEW
`
`3.] Bohr Theory olthe Hydrogen Atom
`Historical Development ol' the Conmpt of Discrete Energy Levels
`Energy Levels of the Hydrogen Atom
`Frequency and. Wavelength ofEnrjssion Lines
`Ionization Energies and Energy Levels of Ions
`Photons
`
`3.2 Quaium Them-y ofAtoIm'r Energy Levels
`Ware Nature of Particles
`
`Heisenberg Uncertainty Principle
`Walre'l'heory
`Wave Functions
`lQuantum States
`The Schrodinger Wave Equation
`Energy and. Wave Hanclion for the Ground State of the
`Hydrogen Atom
`Excited. States of Hydrogen
`Allowed Quantum Numbers for Hydrogen AtomWave Functions
`3.! Angular Momentu- ul' Alums
`l[Ilrlzrital Angular Momentum
`Spin Angulx Monrennrnr
`Total Angular Moms-mm
`LII Fnergy Lereh Afim'laled with DneJIIertron Atoms
`Fine Suucture ofSpectra] Lines
`Pauli Exclusion Principle
`35 Periodic Trilli- ol‘ the Elements
`
`lIlluantram Conditions Associated with Multiple Electrons Attached
`to Nuclei
`
`Shorrlrand Notation for Electronic Configurations ofAmms Having
`More Than Dne Electron
`
`3.6 Farergy Lereh ol' Milli-Electron Atolfl
`Energy-Level Designation for Multi-Electron States
`Russell—Saunders or LS Coupling — Notation forEnergy Levels
`Energy levels Associated with Two- Electrons in Unlilled Shells
`Rules for Ubtaining S, L, and. .l' for L5 Coupling
`Degeneracy and Statistical Weights
`fflmflw
`Isoelentronic Scaling
`
`Efiflflgfi
`
`'57
`
`EEEEEEE
`EEEEEEEEE
`
`
`
`
`
`
`
`

`

`ODH'I'HITS
`
`resonances
`vacuums
`
`4 RADIATNE TRANSITDNS AND EMISSION LINE'WIDTH
`ovenwew
`
`4.] Decay ol'FJcited Stales
`Radiative Decay ofExccited States of kolamd Atoms —
`Spontaneoui Emission
`Spontaneous Emission Decay Rate — Radiative Transition
`Probability
`liletime ol'a Radiating Elecircn — The Elecu'on as a (lassical
`Radiating Harmonic Oscillator
`Nonradiatiire Denay of the Excited States — Collisional Decay
`4.2 Emimion Broadening and Iine'widfll Due to Radiative Decay
`Cluica] Emission linewidth of a Radiating Electron
`Natural Emission linewidlh as Deduced by Quamum Mechanics
`[Minimum linearidth}
`It} Additional FnissiooJlroadening Processes
`Broadening Due to Nomadialiue (Collisionall DecayI
`Broadening Due to Dephasing Collisions
`Amorphous Crystal Broadening
`Doppler Broadening in Gases
`'ltl'oigt Lil-shape Profile
`Broadening in Gases Due to Isotope Shifts
`Comparison of 1t'iuious Types oiEnritaion Broadening
`dual Qtnnlm Mechanical Deseriplion of RadiatingAtoms
`Electric Dipole Radiation
`Electric Dipole Man-i1 Element
`Electric Dipole Transition Probability
`Oscillator Strength
`Selection Rules {or Electric Dipole Transitions Involving Atoms
`with a Single Electron in an Unlilled Subshell
`Selection Rules for Radiative Transitions Involving Atoms wilh
`More Than One Electron in an Unfilled Subshell
`
`Parity Selection Rule
`Inefficient Radiative TracEilions — Electric Quadrupole and Other
`Higher-Order Transitions
`resonances
`vacuums
`
`5 ENERGY lE‘lIl'ELS AI'ID RAMA'IWE PROPERTIES OF MOLECULES.
`LIDUIDS. AND SOLIDS
`ovenwew
`
`5.1 Molecular Energy [reels and Speclra
`Energy Levels of Molecules
`Clmsification of Simple Molecules
`Rotational Energy Levels oilinear Molecules
`Rotational Energy Levels oi Symmetric-Top Molecules
`Selection Rules for Rotational Transitions
`
`SIS
`SIS
`
`S'J'
`s9
`
`9|]
`
`9|]
`
`94
`
`95
`93
`I0]
`I0]
`
`l03
`l05
`III:
`I0?
`Ili'llil
`It)?
`I I4
`I [5
`I [8
`l2]
`I22.
`I23
`I24
`I24
`
`I25
`
`I 2'}
`
`I30
`
`I3]
`I 3]
`I 3]
`
`I35
`I35
`
`I35
`I35
`I 33
`I39I
`I4]
`I4]
`
`
`
`
`
`
`
`

`

`(“TENTS
`
`Vibrational Energy levels
`Selection Rule for Vibrational Tramilions
`Rotational—Vibrational Transitions
`Probabilities ofRotational and Vibrational Transilions
`
`Electronic Energy Levels of Molecules
`Electronic Transitions and. Associated Selection Rules of
`Molecules
`Emission Linewidlh ot'MoIJecular Transitions
`
`The Franck—Condon Principle
`ExcirnerEnergy Levels
`5.2 liquid Energy Levels and Their Radiation Properties
`Structure oi Dye Molecules
`Energy levels of Dye Molecules
`Excitation and Emission of Dye Molecules
`Den'iniental Triplet States onye Molecules
`5.3 Energy Levels in Soids— Dielectric Imr Malerifls
`Host Materials
`
`Laser Species — Dopant Ions
`Namiinewidlh laser Materials
`Broadband Tumble Laer Materials
`
`Broaderling Mechanism for Solid—State Lasers
`5.4 Energy Levels in Soids— Sfilitondnclor Laser Material:
`Energy Bands in Crystalline Solids
`Energy Levels in Periodic Struclures
`Energy Levels ofConductors. Insulators. and. Semioonductors
`Excitation and Decay ot'Exciled Energy Levels — Reoorobination
`Radiation
`
`Direct and Indirect Bandgap Semiconductors
`Electron Distribution Function and. Density of States in
`Semiconduclors
`Intrinsic Serrriconduflor Malerials
`
`Extrinsic Semiconductor Materials — Doping
`p—n Junctions — Recombination Radiation Due to Electrical
`Excitation
`
`Heterojunction Semioonductor Materials
`Quanluro 1|Wells
`Variation of Bandgap Energy and Radiation Wavelength 1urillu
`Alloy Composition
`Reeolnhinalion Radiation Transition Probability and Linetvidlh
`REFERENCE
`MEATS
`
`6 RADIATION AID THERMAL EQUILIBRIUM — ABSORPTION AND
`SIIMULATED EMISSI'JN
`“REVIEW
`
`6.] EquiliIJ-rirll
`Thermal Equilibrium
`Thermal Equilibrium via Conduction and Convection
`Thermal Equilime via Radiation
`
`[43
`[43
`[44
`[48
`[49
`
`[5|]
`[5|]
`[5|
`[52
`[53
`[53
`[55
`[5o
`[52"
`[58
`[58
`[59
`[El
`[615
`[I58
`[I58
`[68
`[TI]
`['3‘2
`
`[T3
`[T4
`
`[75
`[T9
`[T9
`
`[32
`[E4
`[HIS
`
`[9|
`[95
`[95
`[95
`
`[99
`[99
`[99
`[99
`
`
`
`
`
`
`
`

`

`ODH'I'EITS
`
`6.2 Radiating Bodies
`Stefan—Bollzrnann Law
`1Wien‘s law
`[rradiance and Radiance
`
`6.3 Cavity Radiation
`Counting the NumberofCauity Mules
`Rayleigh—Jeans Formula
`Planck‘s Law for Cavity Radiation
`Relationship between Cavity Radiation and Blackbody
`Radiation
`
`Wauelenglh Dependence of Blackbody Emission
`6.4 Alisorplion mid Slimnlaled FWon
`The Principle ofDetailed Balanee
`Absorption and Stimulated Emission Coeffitjenls
`REFERENCES
`PROBLEMS
`
`SECI'IDH 3. LASER AHPLIFIEH
`
`1 CONDITIONS FOR PROEIJEING A LASER — PDPU LATICIN
`INHERSIDHS. GAIN. AND GAIN SATURATION
`OVERVIEW
`
`1.] Alisorplion mid Cain
`Absorption and Gain on a Homogenemisly Broatlened Radiative
`Transition (Lorentzian Frequency Distribulion}
`Crain Coefficient and Stimulated Emission Cross Section for
`
`Homogeneous Broadening
`Absorption and Gain on an Inhomogenetusly Broatlened Radiative
`Transition (Doppler Broadening wilh a Gaussian Distribution}
`Crain Coefficient and Stimulated Emission Cross Section for
`
`Doppler Broadening
`Statistical Weights and Ihe Gain Equation
`Relationship of Gain Coezlficient and Stimulated Emission
`Cross Section toAlisorption Coeffiocient and Absorption
`Cross Section
`
`1.2 Population Inversion I Netemry Condilion [or 3 Inner]
`1.3 Saltmflion Intensity.r {Snffit'ienl Condition for a lanternI
`1.4 Development and Growth of a Laser Beam
`Growlh ot'Beam for a Gain Medium with Homogeneous
`Broadening
`Shape or Geometry ofAmplifying Medium
`Growlh ot'Beam for Doppler Broadening
`1.5 Exponential (Iron-II] Fat'torICa'nI'
`1.6 Threshold Reqtlimmits for a Laser
`laser with No Minors
`Laser with fine Mirror
`laser with Two Mirrors
`BEFEBWCES
`PROBLEMS
`
`2”
`214
`2l5
`2lfi
`2l1
`22]
`22]
`
`225
`225
`225
`
`225
`
`22'}
`
`23B
`
`23]
`232
`
`233
`234
`235
`23E
`
`233
`24]
`
`245
`241
`241
`
`253
`253
`
`
`
`
`
`
`
`

`

`(“TENTS
`
`E LASER OSCILLATION ABOVE Tl-IIESHOLD
`OVERVIEW
`3.] Laser Cain Saturation
`
`Rate Equations oftlle Laser levels That Include Stimulated
`Emission
`
`Population Densities of Upper and LowerLaser levels with
`Beam Present
`
`Small—Signal Gain Coefficient
`Saturation oftlle Laser Gain above Threshold
`
`5.2 Laser Beam Growth beyond the Saluralion Intensityr
`Change from Exponential Growth to Linear Growth
`Steady-State Laser Intensity
`SJ Optimization ol' Laser Outpnl Power
`Optimum Output Mirror Transmission
`Optimum Laser Output Intensity
`Estimating Optimum lmOutput Power
`M Falterg].I Exchange between Upper Laser Igvel Population and
`Laser Photons
`
`DecayI Time ofa Laser Beam within an Optical Cavity
`Basic LaserCatIity Rate Equations
`Steady-State Solutions bBlD‘W laserThresl'nild
`Steady—State Operation above LaserThresholtl
`$5 laser Output Fluctuations
`Laser Spiking
`Relaxation Oscillations
`
`3.6 InserAmplil‘iu-s
`Basic Amplifier Uses
`Propagation ofa High-Power, Short—Duration Optical Pulse through
`an Amplifier
`Saturation Energy Fluenoe
`Amplifying Lortg Laser Pulses
`hmplil'ying Short Laser Pulses
`Comparison ofEfficient Laser Amplifiers Based upon Fundamental
`Saturation limits
`
`Min'or Array.l and Resonator (Regenerative) Amplifiers
`IEFEIENCE
`mum
`
`9 REQUIREMENTS FOR OHTAINIHE POPULATION INVERSIOHS
`OVERVIEW
`
`9.] Invasions and Tm-Iflel Systems
`9.2 Relative Decay Hales — Radiative versus Collisions]
`9.3 Shady-Slate Inversions in Three- and Four-Igtel Systems
`TTumLevel Laser 1with the Intermediate level as the Upper Laser
`Level
`
`Thee-Level Laser 1with the UpperLaser level as the Highest level
`Four-level Laser
`
`9.4 Transient Population Interim
`
`255
`255
`255
`
`255
`
`295
`298
`3|] I
`
`
`
`
`
`
`
`

`

`ODH'I'HITS
`
`9.5 Processes 'l'hal Inhibit orDestroy Intersions
`RadimionTrapping in Atoms and lens
`Electron Collisional Thermalization oi the laserLevels in Atoms
`and Inns
`
`Comparison of Radiation Trapping and Electron Collisional Mixing
`in a Gas Laser
`
`Absorption within the Gain Medium
`REFERENCES
`PRUILEH'IS
`
`1D LASER FUNDING REQUIREMENTS AND TECHNIQUES
`mmmw
`
`19.1 Excitation or PInp'IlnglresIJold Requirements
`10.2 Plumping Pallnrays
`Excitation by Direct Pumping
`Excitation by Indirect Pumping (Pump and Transfer]
`Specific Pump-antl—Transier Processes
`19.3 Specific Exteitalion Parameters Amoeialed with
`Dptieal Pumping
`
`Puntping Requirements
`A Simplified Optical Pumpting Approximation
`Transverse Pumping
`End Pumping
`Diode Pumping of Solid—Stale Lasers
`Charamerizalion ofa laserflain Medium 1with Optical Pumping
`{Slope Efliciency]
`19.4 Specific Emeitalion Parameters Associaled with
`Particle P‘tmtping
`Electron Collisional Pumping
`Heavy Particle Pumping
`A lu'loreArazuraIe Description ofElectrnn Excitation Rate to a
`Specific Energy level in a Gas Discharge
`Elemical Pumping ot'Semiconductors
`REFERENCES
`PRUILEH'IS
`
`SECI'IDH II. LASER RESONATORS
`11 LASER EMT? MODES
`OVERVIEW
`".1 Introduction
`
`".2 Imgiudirul Laser Cal-ig- Modes
`Fahrjr—Perot Resonator
`Fabry—Perot II‘Sa'II'imI Modes
`Longitudinal Laserlflat‘litg.r Modes
`Longitudinal Mode Number
`Requirements {or the Development III'Longjludina]
`Laser Modes
`
`3”
`
`3l5
`3llS
`3l9
`3l9
`322.
`321
`322.
`3254
`32.4
`32?
`339
`
`339
`339
`
`352
`
`355
`355
`359
`
`359
`36]
`363
`
`3?]
`3?]
`3?]
`3?}.
`3?}.
`3?9
`381]
`359
`
`331
`
`
`
`
`
`
`
`

`

`334
`335
`
`336
`391]
`3'5”
`392
`
`CHITEHTS
`
`11.3 Transverse Laser Carly Modes
`Fresnel—Kirchhofi Difl'raetion Integral Formula
`Development oi'Transverse Modes in aCavily with Plane—Parallel
`Minors
`
`Transverse Modes Using Curved. Miners
`Transverse Mode Spatial Distributinns
`Transverse Mode Frequencies
`Gaussian-Shaped Transverse Modes within and beyond the
`Laser Cavity
`I la! Properlies of Imer Modes
`Mode Diameter-ism
`Effect. of Modes on the Gain Medium Profile
`MINES
`PROBLEMS
`
`12 STABLE LASER RESONATORS AND GAUSSIAN BEAMS
`NERVlEH'
`Ill Slable Cru'vrd Min-or Cavities
`Curved. Min'er Cavities
`ABC!) Matriees
`
`Cavity StabilityI Criteria
`Ill Propel-lies otf Cumian Beams
`Propagation of a Gaussian Beam
`Cranssian Beam Pmperties oi'TnI'o-Mirrer LaserCavities
`Properties efSpeciIie Two—ltlfirror Laser Cavities
`Mode Volume era Hermite—Gaussian Merle
`
`IL! Propel-lies otf Real Laser Beans
`ILII Propagation ofGatmsim Beams UsingABCD Matrices—
`Complex Berl- Phrameler
`Complex Beam Parameter Applied to a Two-Mirror LaserCavity
`REFEIIINCES
`PROBLEMS
`
`432
`432
`
`13 SPECIAL LASER CAUITIES AND CAVITY EFFECTS
`OVERVIEW
`Ill Unstable Resonators
`
`13.2 Q-Su'ileliing
`General Description
`'l'heery
`Methods emedueing Q—Switehing within a LaserCavity
`13.! Cinfiwitehing
`1M Mollie-Inciting
`General Description
`Theory
`Techniques for Prndueing Mode—Looking
`135 Pulse ShorleningTeclII'qne-s
`Self—Phase Modulation
`
`Pulse Shnrlenjng er Lengthening Using Group Hecity Dispersion
`Pulse Compression [Shortening] with Gratings or Prisms
`Ultrashort—Pulse Laserand Amplifer System
`
`
`
`
`
`
`
`

`

`ODH'I'HITS
`
`13.6 R'llg Lasers
`Monolithic Unidireclional Single-Mode NszAG Ring Laser
`Two—Mirror Ring Laser
`13.? Complex Beam Parameter Analysis Applied to Mtlti-Mirror
`Imr Cavil'les
`
`Three—Mirror Ring laser Cavity
`Three— or Four—Mirror Fmalsai Cavity
`Illl Cavities for Producing Spectral Narrmling ol‘
`Imr Dutpnl
`Cavin 1with Additional Fabry—Perol Etalon for l‘'llaI:To'It|.r—Ftequ.le|:n::3l
`Selection
`
`Tunable lCavity
`Broadband Tunable cw Ring Lasers
`Tunable Cavity.r for Ulflm-qum‘f l[Ilutput
`Disu'ibuted Feedback {DFB} lasers
`Disuibuted Bragg Reflection Lasers
`15.9 Imr Cavilies Requiring Small-Diameter Cain Regions —
`Aslignalicallgr Compensated Cavities
`13.10 Waveglide Cavities for Gas Insets
`REFERENCES
`molteus
`
`SECTION 5. SPECIFIC LASER SYSTEMS
`
`14 LASER SYSTEMS IWOL'o'IHG lDW—DEHSITY GAIN MEDIA
`WE‘VE“
`14.1 Atomic Gas Lasesa
`Introduction
`Helin—Neon Laser
`
`General Description
`laser Souclnre
`Excitation Mechanism
`
`Applications
`Argon [on Laser
`General Description
`Laser Soucmre
`Excitation Mechanism
`
`Krypton [on Laser
`Applications
`Helin—Cadmiinn Laser
`
`General Description
`laser Souclnre
`Excitation Mechanism
`
`Applications
`Copper Vapor Imr
`General Description
`Laser Soucmre
`Excitation Mechanism
`
`Applications
`
`468
`4459
`4?!)
`
`4TB
`
`4?!)
`41"3
`
`4TB
`
`4TB
`
`4TB
`4RD
`4RD
`4!]
`434
`
`434
`435
`436
`433
`
`49]
`49]
`49]
`49]
`492
`
`492
`493
`494
`
`497
`49?
`49?
`49B
`499
`
`5CD
`50]
`50]
`
`50]
`502
`504
`
`505
`505
`505
`50?
`50?
`
`503
`
`
`
`
`
`
`
`

`

`CONTENTS-
`
`142 Molecular Gas lasers
`Introduction
`Carbon Dioxide laser
`
`Ganara] Description
`Lam Structirra
`Excitation Mechanism
`
`Applications
`Excinar Lasers
`
`Ganara] Description
`laser Su'ucnrra
`Excitation Mechanism
`
`Applications
`Nilrogm Laser
`Ganara] Description
`laser Struct1|ra and Excitation Mechanism
`
`Applications
`Far-infrared Gas Lasers
`
`Ganara] Description
`Laser Structirra
`Excitation Mechanism
`
`Applications
`Gunfire] Lars
`
`Ganara] Description
`Lam Structirra
`Excitation Mechanism
`
`Applications
`14.3 li-Ilay P‘Iasnn lasers
`introduction
`
`li'urrping Energy Requirements
`Excitation Mechanism
`
`Optical Cavities
`X—Ray Laser Transitions
`Applications
`1441 FmAElcctnon Luci-s
`introduction
`Laser Structirra
`
`Applications
`EEFEIENCES
`
`15 LASER SYSTEMS INVOLVING HIIEIH—DEI'MISI'I'W'r GAIN MEDIA
`WINNIE“
`
`15.] Organic Dye Lasers
`introduction
`Laser Structirra
`Excitation Mechanism
`
`Applications
`15.2 Solid-State Lasers
`introduction
`
`51]]
`51]]
`5] |
`5] |
`5] |
`515
`515
`516
`516
`51'?
`518
`52]]
`52]]
`52]]
`52]
`522
`522
`52.2
`523
`523
`524
`524
`524
`524
`524
`525
`525
`525
`525
`52.8
`532
`532
`532
`535
`535
`536
`53':r
`53'?
`
`539
`539
`539
`539
`
`543
`
`545
`545
`
`
`
`
`
`
`
`

`

`54?
`54?
`
`550
`55!]
`55 l
`553
`554
`555
`555
`556
`556
`55?
`55?
`557
`55?
`553
`553
`559
`559
`
`COHI'EITS
`
`Ruby Laser
`General Description
`Laser Structure
`Excilalion Mechanism
`
`Applications
`Neodynl'um ‘i'AG and Chm Luna
`General Description
`Laser Structure
`Excitalion Mechanism
`
`Applications
`Neodynl'umfllf Lasers
`General Description
`laser Structure
`Exeilalion Mechanism
`
`Applications
`Neodynl'umflllr'lml Vanadate I Ndfimdj lasers
`General Description
`Laser Structure
`Excilalion Mechanism
`
`Applican'orn
`YllcrbinnflAG Lasers
`
`General Description
`Laser Structure
`Excilalion Mechanism
`
`Appliun'orn
`Alexandria laser
`
`General Description
`Laser Structure
`Excilalion Mechanism
`
`Applications
`Titanium Squh're Laser
`General Description
`Laser Structure
`Excitalion Mechanism
`
`Applications
`Clint-in USAF and “13th Insets
`
`General Description
`Laser Structure
`Exeilalion Mechanism
`
`Applications
`fiber Lasers
`
`General Description
`laser Structure
`Excilalion Mechanism
`
`Applican'orn
`Color Gutter lasers
`
`General Description
`Laser Structure
`
`
`
`
`
`
`
`

`

`5T4
`5T6
`5T6
`5T6
`579
`5El
`5'3”
`592
`594
`594
`5'96
`59'?
`
`CONTENTS-
`
`Escitation Mechanism
`
`ApplicaIions
`15.! Semiconductor Diode Lasers
`Introduction
`
`Four Basic Types of Laser Materials
`Lam Structure.
`
`Frequency Control ot'Laaer Output
`Quantum Cascade Lasers
`p—Doperl Germanium Lasers
`Excitation Mechanism
`
`Applicalions
`IEFEIENCES
`
`SECTION 6. FREQUENCY MULTIPLIEATIGN OF LASER BEAMS
`1i FREQUENCY MULTIPLICA‘I'IDN OF LASERS AND lIII'ITHEII
`NGILINEAR OPTICAL EFFECTS
`MINNIE“
`
`16.] Wave Propagalion in an AniaolropiJr Crystal
`16.2 Pohriaalion Response of Maleriala lo Lighl
`IL! Second-Order Nordiiear Oplical Puree-flea
`Seeond Harmonic Generation
`
`Euro and Difference Frequency.r Generation
`Optical Parametric Oscillation
`1M Third-Order Nonlinear Optical Proerme-s
`Third Harmonic Generation
`
`Intensity-Dependent Refractive Index — Self-Focusing
`“55 Nonlinear Optical Materials
`“5.6 Phase Matching
`Description of Hiase Matching
`Achieving Phase Matching
`Types of Phase Matching
`16.? Saturable Mraorptim
`16.3 Two-Photon Absorption
`16.9 Slinirdated Rm Scallering
`16.10 Hannonic Cenerltion in Case-s
`IIEFEIENCES
`
`Appendix
`Index
`
`
`
`
`
`
`
`

`

`1 I
`
`ntroduction
`
`NEITHER A laser is a device lint amplifies light
`and plodm'es a higth directional. high-intensity
`beam Ihatmostot'tenhasayerypure frequency or
`wavelength. ltcontesinsirnes ranging from approx-
`imatelyonehenththediamelerofahurnanirajrto
`dresimeofaverylargebuildmginpowersranging
`from [0—9 to I113" W7 and in wavelengths ranging
`fromthemicro'wavemthesoft—X-rayswtndregimrs
`with corresponding frequencies from Ill" to NJ" He.
`lasers havepulseenergiesas highas lll‘l and pulse
`durationsasshortmi s Ill—'5 s Theycaneascilry
`riill holes in the most durable of malerialsandcan
`
`ofexiflence!
`
`weldderachedretinaswilhinthelnlnnneye. TheyI are
`alrey component ofsonle ofour most mulcrn com—
`munication systemsand arethe“phonograph needle"
`ol'ourcolnpactdise players. They perform heattreat—
`rneniofhigh—atrength materials. archas the pistons ol
`curantornnbile engines. and provide a special surgi—
`cal knife for manytypesol'nterfical prnuadnres. They
`act as targetdesignstors for militaryweapons andpro—
`vide for the rapid check-out we have come to expect
`at the supermarket. What a remahahlerangeofclrsr—
`acteristics foradevice Iliatis in onlyI its fifth decade
`
`INTRODUCTDN
`
`There is nothing magical ahmn a laser. It can he thought ofasjust another type
`ol light source. Iteertainly has many unique properties that make it a special light
`source. but these propertiescan be understood without tnowledgeof sophisticated
`mathematiml techniques oreomples ideas. It isthe objective olthis best loesplain
`theoperationolthclaserina simple, logical approach thalhuilds from one con-
`cept In the nestasthe chapters evolve. The concepts, as they are developed, will
`be applied to all classes of laser Inflerials, so that the reader will develop a sense
`ol' the broad lield ol' lasers while still acquiring the mpahility to study, design. or
`simply understand a specific type oI'laser system in detail.
`
`DEFINITION OF THE LASER
`
`The word laser is an acronym for Light Amplification by Stimulated Emission oi
`Radiation. The laser makes use of processes thal increase or" amplify light signals
`aflerthose lgnals have been generated by other means. These processes include
`(I) stimulated emission, a naturifl effect that was deduced by considerations re-
`lating to thermodynamic equilibrium+ and [2} optical feedback {present in most
`
`
`
`
`
`
`
`

`

`
`
`5. 1-1 Frnpilied
`Minoltypicallamr
`
`Fully reflecting
`niror
`
`Optical resonator or Gitl'l‘lj'
`A
`
`Amplltyi'tg rnedlum
`
`Parllallv Irmamflting
`niror
`
`liners) that is usually provided by minus. Thus, in its simplest form, a lmercon—
`sists of a gain or amplifying medium {where stimulated elnimion occurs], and a
`set of minors to feed the Iightlraclt intolhe amplifier for continued growth ot'the
`developing berm, as seen in Figure I-L
`
`srmrcrrv OF A LASER
`
`The simplicity ofa lasercm he understood by intimidating the light from acandle.
`Nomally, a blurring candle radiates light in all directions. aid therefore illumi-
`nates various objects equally if they are equid'mtmt [rain the candle. A lasertfies
`light tllat would nnnndly be emitted in all directions, such as from a candle, and
`concenlnles that light into a single direction. 'l'hus, ifllte light radiating in all di-
`rectiomfloinacandle 1were Ilallntrated into a singlelreun nfthedianeterolthe
`pupil ot'youreye (qrprmtinflely 3 Iran}, and ifyclr were standing adishmce of
`I In from the candle, then the light intensity would he 1,000,000 times in bright as
`the light that you nnnnrdly see radiating from the candle! That is annually the
`underlyingconeept nt'the operuion ofalaser. However, acandle is not the kind of
`medium that prodrces amplification, and thus there are no cantle tuners. It ties
`relatively special conditions within the [riser medium foramplilicatinn to occur,
`htrt it isthat ulcqinhilityI oftaking light that would normally raiifle from asource in
`all directions — Hid concenlrfling that light into abet-n traveling in a single direc-
`tion—lhal is involved in rottingalmer. These specifl eonditiorer, and the media
`within which they are pruiuced, will he described in some detail in Ihis hook.
`
`UNICEE PROFEII'I'ES CI: A LASER
`
`'l'hehearnofljghlgenefiledhyatypiml Imam havernan‘ypmpertiesflratrle
`unirple. 1When comparing later properties to those ofnlher light sources. it can
`be readily recognized that the values of various palarneters for laser light Irther'
`greaflyennedorarernud] morereslrictivelhanflrevaluesfornumymmnnn
`lightsourees. We never use lasers for street illumination. orforillumination within
`our Muses. We don't use them for seudllights or flashlights or re; headlights in
`
`
`
`
`
`
`
`

`

`IHTIIDDIJCTIDN
`
`our cats. Lasers generally have a oanower hemeoe]! distl'ihulion, or much higher
`intensity, or a much gleaterdegtee oleollimalion, or much sinner puhe thrrflion,
`lbanthfl arildile from more common lypesoflight sources. Therefore, wedo use
`lbem in compact d'm: players, in supermarket cheek—out semnera, in sunrejring in—
`staneIIIs, and in medical implications 3 a surgical knife or for welding detached
`retinas. We aha use them in communication: systems and in rail" and roilitalj‘r
`targeting ramification, as well a many other Inn. A hater isu specialized light
`route-e that should be used unfit when its unique properties are required.
`
`THE LASER SPECTRUM am WAVELENG'I'I'IS
`
`A ponion oflbe electromagnetic nilialion alieetnnn is dlown in Figure I—Z for lhe
`region covered by currently existing lasers. Such lasers span lbe wavelength range
`from the lil'iot'm'ed part oflhe speetnrm {l = Lilli urn} lo lhe eoft—X—ra}! region
`[11. = 3 turn), dmbywveringamgeufwavelengfluufalmnelsixudas ofmng—
`nilude. There are several types of units that He used to define laser wavelengths.
`These range from mierometersnrmicmns {rim} in the infrared to mometers {om}
`md algstroms {A} in the visible, ultraviolet{U‘lmr ), vacuum ultraviolet (VUV), ex—
`treme ultraviolet {EUV orJCUV], slid sofl—X—ray (SEER) special regions.
`
`WELEIIG'fl-I IIIII'I'S
`
`I_urn = 10—5 m:
`IA:10‘”m-,
`Inm: Ill—9 m.
`
`Coosetpeatly, l mieroullfum] : 181manEstromefi-i} = LWnaooroetel's {mu}.
`Forexample, green Iighlbfl awmreleoglhoffi x 10‘? m :05 run = SJIIJFI. =
`5M nro.
`
`'_—
`
`.
`i
`-
`.- .
`a
`. FIR Laser:
`
`'
`HF
`
`l
`'_'_'__
`
`Diode
`Re '1'
`
`.-
`Ar..
`
`..
`
`CD
`
`'
`
`__
`
`'
`
`Fur-I14 Wavelength
`rage diva-ins beers
`
`N2
`Hub-r
`KrF
`Han-Ne
`MINAG
`He Cl
`
`Sun-I-Hw
`-.
`-
`Lasers
`
`Ice-f
`
`Ha-He
`
`Far Infrared
`
`
`Inlnutd
`
`9mm: om
`Ti-_.B.IE93
`Visible
`
`in:
`Ulruwolel.
`
`50F. ill-Ray:
`
`Eflpm
`
`10pm
`
`1pm anon-r. 10mm annm 111nm
`3pm
`
`‘-
`
`-—— ENERGY {
`
`3’13 a...
`
`1'
`
`
`
`
`
`
`
`

`

`INTRODUCTION
`
`WELEIIGTH REGIONS
`
`Far infrared: II] to LEI]?! 31m;
`middle infrared: ] to 10 em;
`nearinl'rared: '1'? to I 1.1m;
`visible: 0.4- to 1].? urn, or 400 to "Fill run;
`ultraviolet: 0.2 to {Lt-I run, or 211'] to 400 um;
`vacuum ultraviolet: (1.] to 0.2 em, or III] to ZEN] nrn;
`extreme ultraviolet: Ill to [II] nm;
`sot't X—rays:
`] nm to approximately Ell—30 nm {sortie overlap with EUV].
`
`A BREF HIE'rTlllllflr DF'IHE LASER
`
`l|.'Ihar'|:es Townes took advantage of the stimulated emission procem to construct a
`microwave amplifier, Iefenedloasamser. 'l'bisdevice puiucalacoherent beam
`ot' microwaves to be used for communications. The first maser was produced in
`ammonia vapor lIllvith the inversion between two energy levelsthat produced gain at
`a wavelength ol [.25 cm. The wavelengtln produced in the maserwere compara—
`ble to the dimensions of the device, so extrapolation to the optical regime — where
`wavelengths were five orders ol'magnitnde smaller— was not an obviousetrtersion
`ot' that work.
`
`In 1955, Townes and Schawlow published a paperconceming theiridem about
`extending the mmer concept to optical frequencies. Theyr developed the concept
`ot'an optical amplifier surrounded by an optical mirror resonarrtcavity to allow for
`growth olthe beam. Townes and Schawlow each received a Nobel Prize for his
`worl: in this field.
`
`In 1960, Theodore Maiman of Hughes Research Laboratories produced the
`first laser using aruby crystal as the amplifierandaflashlampas the energy source.
`The helical flashlamp sunotmded a rod—shaped ruby crystal, and the optical cavity
`was lormed by mating the flattenal ends ofthe ruby rod with a highly reflecting
`material. Anintenseredbeamwasobservedtoernergefromtheendoftherod
`when the flasblamp was fired!
`The firstgaslmerwasdevelopedin 196] byAJavarLW. Bennett, and D. I-Iar-
`riott of Bell Laboratories, using a minute at helium and neon gases. At the same
`laboratories, L. FJohrrson and K. Nassau demonstrated the first neodymium laser,
`whichhassirrcebecomeoneofthemostreliablelasersavailable. This was [ollowed
`
`in [9152 by the first semiconductor laser, demonstrated by R. Hall at the General
`Electric Research Laboratories. In 1963, C. K. N. Patel of Bell laboratories dis—
`covered the infrared carbon dioside laser, which is one of the most efficient aid
`powerful lasers available today. Later that same year. E. Bell of Spectra Physics
`dismvered the first ion laser, in mercury vapor. In 1964 W. Bridges oI'Hugbes Re
`search Laboratories discovered the argon ion laser, and in 1966 W. Silfvafl, G. R.
`Fowles, and B. D. Hopkins produced the firm blue helium—cadmium metal vapor
`
`
`
`
`
`
`
`

`

`INTIDDUCTIDN
`
`laser. During Ihatsame yea", P. P. Sorolrinand J.R.Lrltlrard oithe IBM Research
`Liberatoriesdevelopedthe lira Liquid laser using an organicdyedissolved in asol-
`vent, thereby leading to the category oi" broadly tumble lasers. Alsost tltat Lime,
`1W.‘W'alterandco—‘nlior'hers atTRGreponed the lirstcoppervaporlaser.
`The first vacuum ultraviolet laser was reported to occur in molecular hydro-
`genbyR.HodgsonofIBMandindependentlyhyll..Waynantetal.oItheNaval
`Research Laboratories in [970. The firm oi the well-linown rare-gas—halide es-
`ccimer lasers wm observed in xenon fluoride by J. J. Ewing and C. Brarr ol'the
`Avco—Evereu. Research laboratory in I975. In tltat same year, the first quantum-
`well laser was made in a gallium arsenide semiconductor by J. van der Ziel and
`co—worlcers at Bell Laboratories. In I9TIS, l. M. l. Marley and co-workers 8. Stan-
`ford University demonstrated the lirst free—electron laseramplifier operating in the
`infrared at the DD; laser wavelength. In l9‘II'9, Walling and co-workers a. Allied
`CIIernicalCorlmration obtainai broadly tunable Iaseroutputl'rornasolid-statelaser
`material called alesandrite, and in I985 tlte first soft—X—ray laser was successfully
`demonstrated inabigbly imimdsel-ium plasmaby D. Mattltewsartdala'genum-
`her ol co—workers at tlte Lawrence Livermore Laboraorim. In [936, P. It'loulton
`discovered the titanium sapphire laser. In l99l, M. Hasse artd co-workers devel-
`oped the lirst blue—green diode laser in ZnSe. In lm F. Capmso and co—worlrers
`developed the quantum cascade laser. In I996, S. Nakamura developed the first
`blue diode laser in GaN—hmed materials.
`
`In 196], Fox and. Li described the existence ol'rllonant transverse modes in
`a laser cavity. That same yea, Boyd and Gordon obtained solutions of the wave
`equation for confocal resonator modes. Unstrble resonators were demortstrated
`in 1969 by Krupke and. Sooy said were described theoretically by Siegrnan. Q-
`switching was first obtained by hicCJung and I-Iellrvarth in 1962 and described
`later by Wagner and Lengyel. The first mode-locking was obtained by Hargrove,
`Fork, and. Pollack in I964. Since then, malty special cavity arrangements, Ieedhack
`schemes. artd otherdevices have been developed to improve thecontrol, operflion,
`and reliability oflasers.
`
`OVERVIEW OF 'I1'IE BOOK
`
`Isaac Newton described IigIn as small bodies emitted from diining whats-ices.
`This view was no doubt influean by the fact that. light appears to propagate in a
`straight line. Christian Huygens, on the otlter hand, described light as a wave mo-
`tion in which a small source spreads out in all directions; most observed effects —
`including diflracfiom reflection, and refraction —crlt be attributed tothe expansion
`ol'primrl'y wava and of secondary wavelets. The dual nettle of light is still ause—
`l'ul concept, whereby the choice of par1ic|e or wave explanation depends upon the
`effect to he considered.
`
`Section Dneol'this hmkdealswith thefundamental wveprqrertiesofligbt,
`including hIIaIwell's equations, the interaction ol electromagnetic radiation with
`
`
`
`
`
`
`
`

`

`INTRODUCTION
`
`matter, absorption and. dispersion, and cohesence. Section Two deals with the fun-
`damental quantum properties oflight. Chapter 3 deseribm the concept ofdiscrete
`energy levels in momitc laserspufies aodalsohow the [ericdictable ofthe ele_
`ments evolved. Chapter 4 deals with radiflive trattsitions and emission linewidths
`and the probability ol' making tlansitions between energy levels. Cliapter 5 con-
`siders energy levels oi lasers in molecules, liquids, and solids — both dielectric
`solids and. semiconductors. Cliapter 6 then considers radiation in equilibrium aid
`the concepts of absorption and stimulated emission of radiation. At this point the
`student. has the hflic tools to begin building a Imer.
`Section Three considers laser amplifiers. Chapter 'i' describes the theoreti-
`cal hais [or producing population inversions and gain. Chapter 3 examines laser
`gain and operation dJove threshold,Chapter9describes how population inversions
`are produced, and Chapter It.) comidels how sufficient amplification is achieved
`to make an intense Imer beam. Section Fourdeals with laserresonators. Chap-
`ter ll eoreiders both longitudinal and traisverse modes within a lasercavity, and
`Chapter 11'. investigates the properties ofstflile resonators and Gaufiian beams.
`Chapter I] eoreiidels a variety of special laser cavities and effects, including un—
`stable resonators, Q-switching, mode-locking. pulse nan'owing, ring lasers, aid
`spectral narrowing.
`Section Five covers specific laser systems. Chapter 14- describ