LASER FUNDAMENTALS
`
`SECOND EDITION
`
`WILLIAM T. SI LFVAST
`
`School an! 0pm: I CRECIL
`Lhivenily of Central Florida
`
`#15:] CAMBRIDGE
`Egg IINIVERSITY PRESS
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`ASML 1006
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`ASML 1006
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`PUBLISHED BY THE Fl“ svnmcn'rfi OF THE. UNIVERSITY DFCflJIBIJME
`The Fit Hiking, 'l‘rlnpilghn Swat-hum. 1|:in Kingdom
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`Cummfi UNIVERSITY PR“
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`ISBNIIISlI 333450 hum
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`2003055352
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`page 1i:
`xxi
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`xxiii
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`Ulh'c-‘Hb-ihhd—
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`Contents
`
`Prefix: to the Second Hittite?
`
`Piefiree to the First Edition
`
`Acknowledgment:
`
`INTRODUCTION
`WEEVIEW
`[ntro-Iluelion
`Delitilion of lhe Imer
`
`Simplicil].r 0T 2 Laser
`Unique Properties of a Laser
`The Laser Spectrum and “I'avelengths
`A Brief History onlle Laser
`Overview of the Book
`
`SECTION 1. FUNDAMENTAL WAVE PROPERTIES OF LIGHT
`
`2 WE NATURE OF LIGHT — THE INTERACTION CIF LISGHT
`WITH MATERIALS
`mum
`
`2.1 Maxwell’s Etrutions
`2.2 Maxwell’s Wave Equations
`Maxwell's Wave Equations for a Vacuum
`Solution ofthe Genera] 1Wave Equation — Equivalenee of Light and
`Electromagnetic Radiation
`Wave Velocity — Phase and. Ginny Velocities
`Generalized Solution ofdteWave Equation
`Transverse Elocu'omgoetie Waves and Polarized light
`Flow of Electromagnetic Energy.r
`Radiation from a Point Source (Electric {Dipole Radiation]
`2.3 [ntemelion of EIedJuIaglulic Radiation {light} will Matter
`Speed of Light in a Medium
`Maxwell's Equations in a Medium
`Application oI'Maxweil's Equations to Dieiecu'ie Materials —
`Laser Gain Media
`
`Complex Index of Refraction — Optical Constants
`Absorption and Dispersion
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`“I
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`ESEEEE
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`IS?
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`CONTENTS
`
`Estimating Particle Densities ofh‘latetials [or Use in the
`Dispersion Equations
`LI Colman-e
`
`Temporal Coherence
`Spatial Coherence
`REFERENCES
`matters
`
`SECTION 2. FIJHDAHEHTAL GHAHTUH PROPERTIES OF LIE-HT
`
`El PARTIELE NAII'URE OF LIGHT — DISCRETE ENERGY LEVELS
`MEWEW
`
`3.] Bohr Theory ol'the Hydrogen Atom
`Historical Development oldie Concept of Diamete Energy Levels
`Enesgy levels of the Hydrogen Atom
`Frequency and Waveltmgjir oi Emission lines
`Ionization Energiesand Energy levels oflons
`Photons
`
`3.! Quantum Tllem'y ofAtonIiI: Iii-orgy Levels
`Wave Nature ofPanieles
`
`Heisenberg Uncertainty Principle
`Wave'l'heoly
`Wave Functions
`lIlluanturu States
`The Schrodinger Wave Equation
`Energy and Wave Function for dtthound State of the
`Hydrogen Atom
`Excited Staleo of Hyrkogen
`Allowed Quantum Numbers for Hydrogen AtomWave Functions
`3.] Angular Montcalm d' Alums
`l[Ilrlnital Angular Momentum
`Spin Angulx Momentum
`Total Angular Moria-mm
`Jul Entry Levels Afiot'lated with Due-Electron Atoms
`Fine Smtcmre ol' Spectra] Lines
`Pauli Exclusion Principle
`35 Periodic Table 0|” the Elements
`
`lQuantum Condjlions Associated with Multiple Electrons Auachexl
`to Nuclei
`
`Shoahand Notation for Elecn'onic Configurations ol'Atorus Having
`More Than One Electron
`
`3.6 Fnergy Levels ulMtlli-Elednm Atoms
`Eneegy-level Designation for Mold-Electron States
`Russell—Sauruiers or LS Coupling — Notation l'orEnetgyI levels
`Energyl Levels Associated with Two Electrons in Unfllled Shells
`Rules for Ubtalniug 5, L. and I for L5 Coupling
`Degenetacy and Statistical Weights
`Hawks
`Isoeleuronic Scaling
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`COH'I'EITS
`
`memes
`vacuums
`
`II
`
`IUtDlATNE TRANSITDNS AND EMISSION LINE'WIDfl-I
`ovenvrew
`
`4.1 Decay of Excited States
`RadialiveDecajr ofEaeiledStstee oilsolatedhtoms—
`Spontaneous Einiuion
`Spontaneous Emission Decay Rate — Radiative Transition
`I="|'ollial:nilit11I
`lifetime ofa Radiating Electron — The Electron as a Classical
`Radiating Hannonic Oscillamr
`Nonradiative Decay of the Excitai States — Colfisional Decay
`4.2 Emimion Bmdeling and Iinewidlh Due to Radiative Decay
`Classical Emission linenridxli of a Radiating Eliectron
`Naniral Emission Linewidlh as Dedueed by Quantum Mechanics
`(Minimum Linevvidth)
`4.3 Additinnfl Fnission-llroaderling Piece-sees
`Broadening Due to Nomadiative (Collisional) DecayI
`Broadening Due to Dephasing Collisions
`Animphous Crystal Broadening
`Doppler Broadening i.n Gases
`ltl'iJigt Lillihape Pmlile
`Broadening in Gases Due to Isotope Shifts
`Comparison of valious Types ofEnIission Broadening
`44 Quanllli Mechanical Description of Ratlizrfiiigdtoms
`Electric Dipole Radiation
`Electric Dipole Mania. Element
`Electric Dipole Transition Probability
`Oscillator Stmngtli
`Seteclion Rules {or Electric Dipole Transitions Involving Atoms
`will} a Single Electron in an Unlilied Subshell
`Selieclion Rules for Raiiative Transitions Involving Atoms with
`More "Dian One Electron in an Unfillied Subshell
`
`Paiity Selection Rule
`Inefficient. Radiative Transitions: — Electric Quadsupole and Other
`Higher-Order Transitions
`lEFElENCFS
`reactants
`
`5 EMERGI‘Ir lEVELS AND RAMTWE PROPERTIES OF HDEECIJLES.
`LIQUIDS. AND SOLIDS
`ovenvlew
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`5.1 Molecular Energy Levels and Speck-a
`Energy Levels oi Molemles
`Classification of Simple Molecules
`Rotational Energy Levels of Linear Molecules
`Rotational Energy Levels of filmmeu'ie-Top Molecules
`Selection Rules {or Rotational Transitions
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`BIS
`86
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`(“TENTS
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`1I;I"i"l:lrational Energy lentils
`Selection Rule for Vibrational Tmilions
`Rotational—Vibutional Transitions
`Pmbabilities ofRotational and Vibrational Transitions
`
`Electronic Energy levels ofMolaecuIes
`Electronic Transitions and: Associated Selection Roles of
`Molecuies
`Emission Limidlh ofMolecutar Transitions
`
`'I11e Franek—Conadon Principle
`Exciroer Energy levcis
`5.] liquid Energy vatlsand'l'heirllatliatioo Primer-ties
`Structure oi Dye Molecules
`Energy Levels of Dye Moiecuies
`Excitation and Emission of Dye Molecules
`Denim-ma] Triplet States ol'Dye Molecules
`5.3 Faber-g]: Levels in Solds— Dielectric Lflll' Materials
`Host Marm'ats
`
`Laser Species — Dopant Ions
`Namiioewidlh laser Materials
`Broadband Tunable Laser Matesials
`
`Broadening Mechanism for Solid—State Lasers
`5.4 Famgy Levels ill Soids— SHIirondncIor Laser Materiak
`Energy Bands in Crystafline Sofids
`EnergjlI Levels in Periodic Structures
`Energy Levels of Conductors, Insulators. and Sendoond‘nctors
`Excitation and Decay ofEsciled Energy levels — Remmbinstion
`Radiation
`
`Direct and Indirect Bandgap Semiconductors
`Electron Distribution Function and Density of States in
`Semiconductors
`Intrinsic Sermoonductor Maleriais
`
`Extriruie Semiconductor Materials —Doping
`p—n Junctiqu — Recombination Radiation Due to Electrical
`Excitation
`
`lQuantum WEIIE
`1|Illaiation of Bandgap Energy md Radiation Waselengdi with
`Alloy Composition
`Recombination Radiation Transition Probability and Limewidlh
`IEFEIENC-
`[HELENE
`
`in RADIATION All} THERMAL EQUILIBRIUM — ABSORI’TIDH AND
`SIMULATED Ems-SKIN
`INTERVIEW
`
`6.] Equilibriu-
`111ermal Equilibn'nro
`Thermal Equilibrium via Conduction and Convection
`Thermal Equilibliuro via Radiation
`
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`ODNTHITS
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`6.2 Radiating Bodies
`Stefan—Boltzmann law
`Wien‘s Law
`[rradianoe and Radiance
`
`6.3 Cavity Radiation
`Counting the Number oflCa'Iiit31I Modes
`Rayleigh—Jeans Formula
`Planck’s Law for 'I'ila'ti'it]r Radiation
`Relationship between Cavity Radiation and Bladrbcdy
`Radiation
`
`Wavelength Dependence of Blackbody Emission
`M Absorption and Stimulated Ewan
`The Principle ofDetaihad Balance
`Absorption and Stimulated Emission Coefficients
`MINES
`PROBLEMS
`
`SECTlD'N 3. LASER AMPLIFIERS
`
`T CONDITIONS FOR PEDEIJEING A LASER — POWLATIDN
`INVERSIDNS. GAIN... AND GAIN SATURATION
`CW'ERVIEW
`
`1.1 Absorplion and Cain
`Absorption and Gain on a. HomogeneousI},l Broadened Radiative
`Transition (Lorentzian Frequencjr Distribution)
`Gain Coefficient and Stimulated Emission Cross Seuion For
`
`Homogeneous Broadening
`Absorption and Gain on an Ildmmopsneously Broadened Radiative
`Transition (Doppler Broadening with a Gaussian Disn'ibution)
`Gain Coefficient and Stimulated Emission Crow Section for
`
`Doppier Broadening
`Smistical Weights and the Gain Equation
`Relationship of Gain Coezlflcient and Stimulated Emission
`Goes Section to Absorption Coefliraent and Absorption
`Cross Section
`
`1.2 Population Inversion I ”memory Condition for a [M]
`1.3 Stalin-alien Intensity.r {Stlffirienl Condition for a LaserlI
`14 Development and Growth of a Laser Beam
`Chowth ot'Beam for a Gain Medium with Homogeneous
`Broadening
`Shape or Geometry offimplifying Medium
`Chianti] ot'Beam for Doppler Broadening
`15 Equinenfial Crawl]: Fartor {Gin}
`Id Threshold Bequimnents for a Laser
`laser with No Minors
`laser with fine Mirror
`laser with Two Mirrors
`REFERNCEE
`PROBLEMS
`
`2!]
`214
`2l5
`2H5
`2!?
`22]
`22]
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`CEIITEHTS
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`LASER OSCILLATION hflO'lI'E ‘l'I-IIESHOLD
`OVERVIEW
`IL] Laet- Cain Saturation
`
`Rate Equations ot'rhe. Laser levels Thai lnclutte Stimulated
`Emission
`
`Population Densities ot' Upper and Lower Laser levels with
`Beam Present
`
`Emil-Signal Gain Coefficient
`Saturation ofthe Laser Gain above Threshold
`
`3.2 Imer Beam Growth beyond the Saturation Intemit}r
`Change from Exponential Growth to Linear Growth
`Steady-State Laser Intensity
`5.1 Optimization ol' Imr Output Hirer
`Optimum Output Minor Transmission
`Optimum Laser Output Intensity
`Estimating Optimum lmOutput Power
`M Falergy Estellalge between Upper Laser Level Population :lll
`Imer Photons
`
`DecayI Time ofa laser Beam within an Optical Cavity
`Basic Laser Cavity Rate Equations
`Steady-State Solutions below Laser Threshold
`Steady—State Operation above Laser'thresholtl
`85 Laet- Oulpli F'Illt't'uiiions
`Laser Spiking
`Relaxalion Oscillations
`
`8.6 Laser Amplifiers
`Basic Amplifier Uses
`Propagation oi'a High-Power, Shou-Druation Oplical Pulse “trough
`an hmpiitier
`Sanitation Energy Flucnce
`Amptifying Long Laser Pulses
`hmptifying Short Laser Pulses.
`Comparison oEFfiIcicnt Laser Amplifiers Based upon Fundamental
`Saturation Limits
`
`MIITDI' Array and Resomtot (Regenerative) Amplifiers
`IEFEIENC.
`flaunts
`
`REQUIREMENTS FOR OBTAINING POPULATION INVERSIOHS
`OVERVIEW
`
`9.] Inversion: and Two-Iflel Systems
`9.2 Relative Decay Hales — Radiatiee mm Coflkional
`9.3 Steady-Slate Intrusions in Three- and Foorallet'el Systems
`ThrmLevcl Laser 1with the Intermediate Level as the Upper Laser
`level
`
`“tree-Level Laser lwith the Upper [.aser level as the Highesl Level
`Hour-level Laser
`
`“.1 Transient Population [overdone
`
`255
`255
`255
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`255
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`COH'I'EIITS
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`9.5 Pmcesses Thal [lilihit orDestroJ‘ Inversions
`Radiation Trapping in Atoms and lens
`Electron Collisionai T‘hczmalization of the Laser Levels in Atoms
`and Inns
`
`Comparison oi Radiation Trapping and Electron Collisional Mixing
`in a. Gas Laser
`
`Absorption within the (fin Medium
`“TERMS
`PEDILEHIS
`
`1D LASER WM’ING REQUIREMENTS AND TECHNIQUES
`CWEINIE‘W
`
`10.1 Excitalion or PtIIp'IIgTIIresIJoId Requirements
`10.2 Plumping Pallet-rays
`Excitation by Direct Pumping
`Excitation by Indirect Pumping l[13"nmp and Transfer]
`Specific Pump—and—Transfer Processes
`10.3 Speeifie Emeilalinn Parameters Amoeialed with
`Optical Pumping
`Ptunping Geometries
`Puntping Requirements
`A Simplified Optical Ptunping Approximation
`Transverse Pumping
`End Pumping
`Diode Pumping of Sofia—State Lasers
`Charactefization ol'a LaserGain. Medium 1with flptical Pumping
`{Slope Efficiency]
`10.4 Speeifie Emeilalinn Parameters Assoeialed with
`Particle Pumping
`Electron Collisiona! Pumping
`Heavy Punch: Pumping
`A MoreAmuraIe Description ofElectron Excitation Rate to a
`Specific Eneugy level inaGas Dischuge
`Elemrical Pumping ofSemiconduotors
`“TERMS
`PEDILEMS
`
`SECTION II. LASER RESONATORS
`
`11 LASER EMT? MODES
`OVERVIEW
`“.1 Introduction
`
`".1 Longiudinal Laser Cat-Hy Modes
`Fahry—Perot Resonator
`Fahry—Pemt Cavity Modes
`Longitudinal. Last: Cavity Modes
`Longituttirtai Mode Number
`Requirements for Idle Development oi Longitudinal
`Laser Modes
`
`3!]
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`315
`336
`319
`319
`322
`322
`322
`3254
`324
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`334
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`392
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`(“TENTS
`
`11.3 Transverse Laser Caviy Modes
`Fresnel—Kirdihofi Difl'raelion Integral Formula
`Development ochransverse Menzies in a Cavity with Plane-Parallel
`Mirrors
`
`Transverse Modes UsingCurvod Mirrors
`Transverse Mode Spatial Distribulions
`Transverse Mode Frequencies
`Gaussian-Shaped Transverse Modes within and beyond the
`[M Cavity
`11.4 Properties of laser Modes
`Mock. amulet-ism
`EfEeot of Modes on the Cain Medium Profile
`IEFEIENCI
`PROBLEMS
`
`12 STABLE LASER RESONATORS AND GAUSSIAN BEAMS
`OVERVIEW
`111 Stable Cm'ved Min-or Cavities
`Curved Minor Cavities
`ABCD Matiiees
`
`Cavity StaliiiityI Dire-sin
`1L2 Propel-lies of Carmina Beams
`Propagation of aGaussian Beam
`Craussian Beam Pmperties ofTvvo-Mimor laserCavities
`Properties ofSpeoilic Two—Mirror Laser Cavities
`Mode 1lil'oluoie ofa Hermite—Gaussian Mode
`
`IL! Properties of Real Laser Beats
`1L1 Propagmion offlaimim Beam UsingABCIJ Matrices—
`Complex litur- Phrarneler
`Complex Beam ParameteeApplied to a Two-Mirror laserCavity
`IEFEIENCU
`PROBLEMS
`
`432
`432
`
`13 SPECIAL LASER CflflTIES AHD CAVITY EFFECTS
`OVERVIEW
`13.1 Umble Resomlors
`
`13.2 Q-Suileliing
`General Description
`'l'heory
`Methods omedueing Q—Switehing within a laser Cavity
`13.3 CinuSwitehing
`13.4 Mode-Inciting
`
`Then
`Techniques for Producing Mode—Locking
`13.5 Pulse ShofleoingTedII'ques
`Seif—P‘lrase Moduialion
`
`Pulse Shortening or lengthening Using Group Veioeity Dispersion
`Pulse Compression [Swimming] with Dealings or Prisms
`[fluashort—Pulse laserand Amplifer System
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`mm
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`13.6 Rig Lasers
`Monolithic Unidireclionai Single—Mode Nd:YAfl Ring Laser
`Two-Murat Ring Laser
`ll? Complex Beam Parameter Analysis Applied to Haiti-Mirror
`Laser Cavities
`
`Three—Mirror Ring Laser Cavity
`Three— or Four—Mirror Braised Cavity
`153 Cavities for Producing Spectral Narrowing of
`Laser Output
`Cavity Iwith Additional Fahry—Pesot Etaloo for Natrow—Frmpleocy
`Selection
`
`Tunable Cavity
`Baoadhami. Tunable cw Ring Lasers
`Tunable Cavity for Ultlanarmw-Eequency Output
`Distributed Feedback {DFB} Insets
`[lisu'ibuted Bragg Reflection Lane
`15.9 Laser Emilie-s Requiring Small-Diameter Gin Regions —
`Asligllalically Compensated Cavities
`13.10 Waveglide Cavilies for files 1%
`REFERENCES
`moments
`
`SECHDH 5. SPECIFIC LASER SVFTEHS
`
`14. LASER SEEMS IWOL'VIHG LDW—DEHSFF‘I‘ GAIN MEDIA
`mmtEt-v
`14.1 Atomic Gas Inset:
`Introduction
`Helm—Neon Laser
`
`General Destz'iption
`laser Structure
`Excitation Mechanism
`
`Applications
`Argon [on Laser
`General Desuiption
`Laser Structure
`Excitation Mechanism
`
`Krypton [on laser
`Applications
`Helm—Cadmium Laser
`
`General Desta'iption
`Laser Structure
`Excitation Mechanism
`
`Applications
`Copper Vapor Laser
`General Description
`Laser Structure
`Excitation Mechanism
`
`Applications
`
`463
`469
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`CHITEHTS
`
`I42 Molecular Gas lasers
`Introduction
`Carbon Dioxide La"
`
`General Description
`Laser Structure
`Excitation Mechanism
`
`Applications
`EIciIIer Lasers
`
`Coma] Description
`Laser Slrocmre
`
`General Description
`laser Structure and Emeilalion Medlenism
`
`Applicalions
`Far-[rtfrared Gas Lasers
`
`General Description
`Laser Slrocmre
`ExcisaIion Mechanism
`
`ApplicaIions
`Unmical Lasers
`
`General Description
`Laser Sti'ocmre
`Excitation Mechanism
`
`Applicalions
`14.3 X‘Ilay Plasnn lasers
`lnlrortoction
`
`Partying Energy Requiremems
`ExcisaIion Mechanism
`
`Dpljcal Cavities
`JC-Ra}I Laser Transitions
`Applications
`I441 FmAl-Ikctroo Lars
`Introduction
`Laser Slrncmre
`
`Applications
`REFERENCES
`
`15 LASER SYSTEMS IIIW'DDI‘ING HII.‘1|H-IIIIE!!.ISIT"Ir GAIIII MEDIA
`MERIT“
`
`l5.l Organic Dye Lasers
`InimdmIion
`Laser Stromre
`Excitation Mechanism
`
`Applicalions
`15.2 Solid-State Lasers
`lnlmdoetion
`
`5H]
`5H]
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`532
`535
`535
`5315
`537
`53'?
`
`539
`539
`539
`539
`
`543
`
`545
`545
`
`
`
`
`
`
`
`

`

`55 l
`553
`554
`555
`555
`556
`556
`55?
`55?
`55?
`55?
`553
`558
`559
`559
`
`CONTENTS
`
`Ruby Laser
`General Description
`Laser Slnlfiure
`Exdtaiion Moduluism
`
`Applimiions
`Nendg'ninm ‘HLG and Glam Imus
`Genera! Deecription
`laser Slmcture
`Emilalion Meclmlism
`
`hpplicalions
`Neodynl'umfllili' lasers
`General Description
`Laser Emmott:
`Excitalion Maximilian
`
`hpplicalions
`Neodyninmflflrilm Validate I NdfiVfldj lasers
`Genera! Description
`Laser Sumre
`Excilalion Medlanism
`
`Applicalions
`YllcrbimlflAG Lasers
`
`Genera! Descriptim
`Laser 5mm
`Emilalion Mechanism
`
`Applicalions
`Alexandrina laser
`
`Genera! Description
`Laser Suucture
`Excilalion Medlanism
`
`Applicalions
`Tilaniml Sapplire laser
`General Description
`Laser Strucium
`Excilalion Mexiunism
`
`hpplicalions
`Chm-in USAF and IjCAF 1m
`
`Genera! Description
`laser Smmre
`Excilalion Medunism
`
`hpplimlions
`Fiber Lasers
`
`General Description
`Laser Smart:
`Emilalion Mechanism
`
`Applicalions
`Color Carter Lasers
`
`Genera! [htriptim
`Laser 5mm
`
`
`
`
`
`
`
`

`

`5T4
`5M
`STE:
`STE:
`5]“)
`SEI
`55”
`592
`594
`594
`596
`59'?
`
`CHITEHTS
`
`Excitation Mechanism
`
`Application
`I53 Semiconductor Diode Liners
`[ntroriudion
`
`Four Basic Types of Laser Materials
`Laser Strumno
`
`Frequency Control of 1m l[Ilutpnt
`Quanmro Cascade. Lam
`p—Dopori Gamartium Lasors
`Excitation Mechanism
`
`Applications
`MINES
`
`SECTIEII 5. FREQUENCY HULTlPllEATIDH OF LASER BEAMS
`1E FREQUENCY MULTIHICA‘I'IDH OF LASERS AND lIZIITi-lElit
`HGILINEAR OPTICAL EFFECTS
`“REVIEW
`
`16.] “Saw Propagation in an Anisotropic Cryslal
`16.2 Polarization Rupolfle oI'MaleI-ials lo Ijghl
`16.1 Second-Order Nord'noar flplit'al Prone-flea
`Sooond Hzroonic Carnation
`
`Euro and Difference Frequency Goraation
`Optical Paramotrio Oscillation
`“5.4 Third-Order Nonlinear Optical Procrme-s
`Third Harmonic Guloralion
`
`[ntonsitjr—Dopondont Refractive. Index — Self-Focusing
`I65 Nonlinear apical Materials
`I615 Plime Matrliiog
`Description offline Matnhing
`Adhering Erase: Matching
`Typos of Phase Matching
`I65." Saturable Absorplim
`I63 TwoLP‘hoton Almrrption
`I63 Slinlrdated Rinmm Scanning
`16.10 “anionic Generation in Case-s
`REFEIENCES
`
`Appendix
`Index
`
`
`
`
`
`
`
`

`

`1 I
`
`ntroduction
`
`it"t‘IFEII'tIIE'tIr A laser is a device that amplifies light
`31d pmdums a highly directional. high-intercity
`beam Ihatmofioftenhasavery pure fiequencynr
`wavelength. ltcomesinsiaes ranging [tom approx-
`irnatelyonetemhthediamelerofahnlnanhairto
`Ihesieeofaverylargebnilding.inpowersranging
`from [0—9 to Illa" W. and in wavelengths ranging
`fi'omdtemicrowavemtllesoft—X-raysmualregions
`with corresponding frequencies from ill" to lll" Hz.
`lmrshavepulseenergiesashighas “1‘1 and pulse
`dumtionsasshortmfi x Ill—'5 5.
`'l'heycanII-ly
`iiifllnlesinthetnostdurahleofmaaarialsandcan
`
`of esiaenee!
`
`welddetaclaedletinaswidiintlselmtnaneye. They ate
`a key component nfsmneol' our most modern com-
`Imnicaticn systemsaiad aielhe“phcmg1aph needle"
`ol'ourcotnpnctdisc players. They perform Ileattreat-
`lnentolhigh—sn'ength materials. sucha the pistons ol'
`ourantotnobile engines. and provide a special surgi—
`calknife for many lypesotmedieal procedures. They
`aclaslargetdesigtratcrs for military weapons andpro—
`side for Ilse rapid check-out we Irate come to expect
`at the supermarket. What a rernal'hahlelangeol'chm-
`aeleristics foradetriee thatis in only its fifth decade
`
`INTRDIIMCTDN
`
`There is nothing magical about a laser. It can be thought ofasjust another type
`ol light source. Itcertainly has many unique properties that make it a special light
`source. but these propertiescan be utalerstond without tnnwledgeof sophisticated
`mathematical techniques orcomple‘s ideas. It isthe objeuive ofthis text toesplain
`theoperationolthelaserina simple, logical] approach thathuilds fromone con—
`cept to the neatasthe chapters evolve. The emcepts, as they are developed, will
`be applied to all classes of laser rnflelials, so that tlae reader will develop a sense
`ol' the broad lield ol' lasers while still acquiring the capability to study, design, or
`simply understand a specific type of laser system in detail.
`
`DEFINITION OF THE LASER
`
`The word laser is an acronym for Light Amplification by Stimulated Emission ol
`Radiflion. The lfler makes use of processes that increase or amplify light signals
`aflerthose agnals have been generated by other means. These pro-rm include
`(I) stimulated emission, a naturifl effect that. 1was deduced by considerations re-
`lating to thermodynamic equilibrium. and [2} OPT-lea! feedback {present in most
`
`
`
`
`
`
`
`

`

`III'I'IIOIILNTI'IDH
`
`Optical resonator or cit-tit;I
`A
`
`Amplltyitg rnedlum
`
`
`
`FF- 1-1 Franliecl
`schematic eitypical hmr
`
`Fully reflecting
`niror
`
`Perllallv trans-Inning
`niror
`
`lfiers) that is usually ptuvided by minors. Thus, in its simplest [can], a Imercon—
`sists of a gain or amplifying medium {where stimulated emim'ion occurs], and a
`setofmirrors to feed the Iighthack intothe arrailifierforeontinued growthofthe
`developing beam, as seen in thtl'e l-l.
`
`Slltl'lJCI'l'Y OF A LASER
`
`'l'hesimplicityofalasercm heunderstoodhy considering the light from acandle.
`Normally, a burning candle radiates light in all dilections. and therefore illumi—
`nates various objects equallyI if they are equidistmt From the caldle. A. lasertates
`light tltat would nonndly be emitted in all diredions, such as from a candle, IIICl
`concentrates that light into a single direction. 'l'ltns, ifthe light mdifling ill all di—
`recfionshomacmfllewemmflahedinbasingleheunoifltediarmterofflte
`pupil lit—your eye (approximately 3 mm), and ifym were slanting adistartce of
`l m from the candle, then the light intermity would he Lilli}!!! times a bright as
`the light that you notnttall}.r see radiating from the candle! That is essentially the
`tutderlyingcolmeptol’tlte opertiion ofalaser. However, acandle is not the kind of
`medium that pro-dices amplification, and thus there are no cantle liners. It takes
`relativer special conditions within the laser medium for amplification to occur,
`but it isthat cqiahilityoflaking light that wotfld “normallyI Iaditle from asoume in
`all directions — and concentruing that light irtto abet-n traveling in a single direc~
`tion—thai is involved in matingalaser. 'I'heae specitd conditioner, and the media
`within which they are pruiucul, will he described in some detail in this tuck.
`
`UNICEE PROPER'I'ES OF A LASER
`
`Tl'teteamofhglugeneraedhyatypicallasumhavemanypupeniesfltatae
`unique. When oompafirtglaalerpropetfiestoflloaeofotherfiglflammitcm
`be readily recognized that the values of various puameters for laser light Itther
`gjeatlyexmedoraremuchmorerestricfivedianfltevfluesfornmyconmmn
`lightsotucee. We never use lasers for street illumination. orforillumination within
`our houses. We don't use them for searchlights or flashlights or as headlights in
`
`
`
`
`
`
`
`

`

`INTHDIJCTIDN
`
`our ears. Lasers generallyI have a narrower firulueney distributielr, or much lriglrer
`intensity. or a much greaterdegree oleolljrneuaon, or much shorter pulse duraion,
`thanlhat available from more common [fluofliglrt sources. Therefore, we do use
`them in compact dist: players, in supermarket cheek—out steamers. in surveying in—
`struments, and in medial] applications as a surgical knife or for welding detadred
`retinas. We also use them in communications systems and in rarhr and roilitrrr].r
`targeting applications, as well as man]I other areas. A truer is a spa'ialized light
`source that should he used only when it: uniquepropeflier are required.
`
`THE LASER SPECTRUM All) WAVELENGHES
`
`A portion ofthe electromagnetic radiation firestorm is shown in Figure l—Z for the
`region covered by currently existing lasers. Suelr lasers span the wavehrgth range
`from the lariofrrlert part Dime spectrum {1. = LII!) run} so the sofl—X—rny region
`[11. = 3 nm), thereby covering a range of wavelengths ofalrnerrt six orders nfnrag—
`nitude. There are several types ol' units that are used to define laser wavelengths
`These range from miemnretersnrnrierurs {run} in the infrared to nanometersfnm)
`and angstroms {A} in the visible, ultravioletthV ), vacuum ultraviolet {VUV}, e1—
`Ireroe ultraviolet {EUV orXUV], and soft—X-rav (SH) spectral regions.
`
`WELEMG'fl-I "HITS
`
`tum =10‘E m:
`is: Isl-“m;
`Inm: [ll—9 In.
`
`Consequently, 1 micron {um} : |fl1mangstrorne {A} = Lillllnanorneters {mo}.
`Forexanurle. green lightbas aweveleogrhoffi x 10—1 m =I}.5 urn = 5,0003. =
`SEN) nro.
`
`.____
`
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`
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`
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`
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`
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`KrF
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`
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`
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`
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`
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`
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`
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`
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`
`5st: Ill-Rev:
`
`sonm 1mm
`
`
`
`
`
`
`
`

`

`IHTIIDDUCI'IDH
`
`lMMlELEIIIETl-I IIEGIDHS
`
`Far infrared: II] to LII!) gm;
`middle infrared: ] to 10 1.1m;
`near inl'rared: 0.? to l 1.1m;
`visible: 0.4- to ll? lpun. or Mm ill) nrn:
`ultraviolet: flQmDJ-I um. orfltommn;
`vacuum ultraviolet: 9.] to 0.2 Jutmf or III] to Warn;
`extreme ultraviolet: 10 to It'll] om;
`soft X—rays:
`] nm to approximately 241—30 nm {some overlap with EUV].
`
`A. BEEF HISTORY OF 'IHE LASER
`
`Chastes'l'oarnea took advantage DIUZB stimulated emission process toconstruct a
`microwave amplifier, referredtoasamaser. This device ptflucedacoherent beam
`of microwaves to be used for communications. The first Inaser 1was prorhiced in
`ammonia vapor with the inversion between two energy levelsthat producedgain at
`a wavelengfll oi LES cm. The wavelengths produced in die maservvere compara—
`ble to the dimensions of the device, so eanapfiafion to the optical regime — when:
`wavelengths were five orders ol'rnagnitucle smaller— was not an obviousestension
`of the. 1work.
`
`In 1953, Townes and Scltewlow publisher! a paper concerning theiridem about
`extending the rnaser concept to optical frequencies. They developed the concept
`ofan optical amplifier surrounded by an oplical rnirror resonant cavity to allow for
`yowfllotthe beam. TownesandSchawloneecb receivedablobel Prime forhis
`work in this field.
`
`In 1960, Theodore Maiman of Hughes Research laboratories produced the
`first laser using aruby crystal as the aanlifierandaflashlampfl the energy source.
`The helical flashlamp surrounded a rod-shaped ruby crystal, and the optical cavity
`waslonnedbymatingdteflattenaiendsoflhenlbyrodwilhahighly reflecting
`material. Anintenseredbeamwasohservedtoernerget'rmntheend oftherod
`when the flasblarnp 1was fired!
`The firstgaslaserwmdevelopedin l'EIGI byAJavan, W. Bennett. and D. Hm"-
`riott. of Bell Laboratories, using a mixture of helium and neon gases. At the same
`laboratmies, I... FJohnson and K. Nassau demonstrated the first neodymium laser+
`whichhassincebecomeoneofthernofireliable lasersavailable. Thiswas Io-Ilowed
`
`in [962. by the first semiconductor laser, demonstrated by R. Hal] al the General
`Electric Resealch Lmoratorile. In 1963, C. K. N. Patel of Bel] laboratories dis—
`covered the infrared carbon dioxide laser. which is one of the most efficient aid
`powerful lasers available today. Later that same year, E. Bell of Spectra Physics
`discovered the first ion laser, in mercury vapor. In 1964 W. Bridges of Hughes Re
`search Laboratories discovered the argon ion Iaeer, and in I'Elfifi W. Silfvm, G. R.
`Fowles, and B. D. Hopkins produced the first blue helium—cadmium metal vapor
`
`
`
`
`
`
`
`

`

`INTRODUCTION
`
`laser. Duringthatsame year, P. P.Sorol:inand J. R..Lankard oftlte IBM Research
`Laboratories developedtlte first. liquid laser ulng anorganicdyedissolved in am]—
`vent, thereby leading to the category of broadly tunable lasers. Also at that time,
`1W.‘Walterandcn—worlcers atTRGreponed the firstcoppervaporlaser.
`The first vacuum ultraviolet laser was reparted to occur in molecular hydro-
`gen by R. Hodgsnn ofIBM and ir|.1:lepen4|:lentlyr by It. Waynantet al. ofthe Naval
`Research laboratories in l9'l'll. The first of the well—ltnnwn rare-gas—halide ear—
`ccinterlasers was observed insemnfluoridebyl. J. EwingandC. Bratrolthe
`Avco—Emett Reaeuch laboratory in [W1 In that same year, the first quantum—
`well laser was made in agallium arsenide semiconductor by I. van der Ziel and
`ctr—workers at Bell Laboratories. In I'l'i'fi, i. M. 1. Marley and co-wrliers 3 Stan—
`ford University demonstrated tlte first free—elemron laserainplifieroperating in the
`infrared at the DD; laser wavelength. In I'J'l'}, Walling and ctr-workers rt Allied
`CllenlicalCorporation obtained broadly tunable laseroutptltfrornasnlidustatelaser
`material called flexanrbite, and in I'JBS the first sofl—X—ray laser was successfitlly
`demonstrated inabigbly imieedseleoiunt plasrnaby D. Matthews andalagennm—
`ber of ctr—workers at the lawrence Livennore Laboratories. In [936, F. Moulton
`discovered the titanitnn sapphire laser. ln NHL M. Hasse arid cn—workers devel—
`oped the first blue—green diode laserin ZnSe. In 19% F. Capmso and co—worters
`developed the quantum cascade liner. In 1996, S. Nakalntuadeveloyed the first
`blue diode laser in GaN—based materials.
`
`In l96l, Fox and Li described tlte existence ofresonant transverse modes in
`a laser cavity. The! same yew, Boyd and Gordon obtained solutions of the wave
`equation for confocal resonator modes. Unstrble resonators were demonstrated
`in 19159 by Krupke and Sony and were described theoretically by Siegrnan.
`[.3—
`switching was first obtained by Mung artd I-Iellwarth in 1962 and described
`later by Wagner and Lengyel The first mode-locking was obtained by Hargmve,
`Fork. and Pollack in [964. Since then, mraty special cavity arrangements, feetfltaclt
`schemes. and otherdevices have been developed to improve thecontrol. openiitlt.
`and reliability of lasers.
`
`OVERVIEW OF 'I1'lE BOOK
`
`Isaac Newton described light as small bodies emitted from shining substances.
`This view was no doubt influenced by the fact that light appetus to propagate in a
`suaigbt line. lI'Jtrimian Huygens. on the other hmd. dficribed ligltt as a wave mo-
`tiort in which a small source spreath out in all directions; tnnst observed effects —
`including diffraction, reflection, and refraction —Cfll be attribtrledto-the expansion
`ofprimary waves and of secondary wavelets. The dual more of light is still anse—
`ful concept, whereby the cltoice of particle or wave explanation depends upon the
`effect to be considered.
`
`Section One nl'tltis book deals with the fundamental wave properties of light,
`including Maxwell's equations. the interaction at electromagnetic radiation with
`
`
`
`
`
`
`
`

`

`iHTRDDUCTIOII
`
`matter, absorptionand dispersion,and coherence. Seetion'l'wo deals withlhe fun—
`damental quantum properties ofligilt. Chapter 3 describes the concept ofdiscrete
`energy levels inmnmic laserspeesll antialsollow the periodictable ofrheele—
`merits evolved. Chapter 4 deals vivid] radiative tralisiliorts and emission linewitiths
`and the probability of making tlansitims between energy levels. Chapter 5 con—
`siders erterg},r levels not lasers in nmlecules, liquirh, and solids — both dielectric
`solids and semiconductors. Chapter I5 then considers radiation in equilibrium aid
`1he mnoepts of absorption and stimulated emission oi" radiaiion. At this point the
`student has the basic tools to begin building a Iuer.
`Section Three considers laser amplifiers. Chapter '1" describes the theoreti—
`cal basis for producing population inversions and gain. Chapter 5 examines laser
`gain andoperation drove thieshold.Cltapter'9describes how population inversions
`are produced, and Chapter lil considers how sufficient amplification is achieved
`tomalreanintenselaserbeam. SeelionFourdealswiflllaserresonflors. Chap-
`ter ll cornitiers bod] longitudinal and transverse modes within a laser cavity, aid
`Chapter l2. investigates the properties ofstflile resonators and Gaussian beams.
`Chapter [3 considers a variety of specitd liner cavities and effects, including un—
`stable resonators, Q-swileliing, mode-locking. pulse mowing. ring lasers, aid
`spectral narrowing.
`Section Five aims spastic: laser systems. Chapter 14- diatribe-5 eleven of
`file most well-known gas and plasma laser systems. Chapter I5 considers twelve
`well-blown dye [wars and solid-state lmers, including both dielectric solid-stale
`lasers and semiconthielor lasers. The book concludes with Electron