LASER FUNDAMENTALS
`
`SECOND EDITION
`
`WILLIAM T. SI LFVAST
`
`Sclmol all Opfics J’ CRECIL
`Lhivenily of Central Florida
`
`4:] CAMBRIDGE
`@155: UNIVERSITY PRESS
`
`
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`
`
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`
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`ASML 1006
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`ASML 1006
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`

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`PUBLISHED BY THE PIE STN'DEalTE OF THE. UNIVERSITY DFCAHBBJIIIE
`The P‘il Hiking, 'Ihupinghn Slnael. club-mum Kim
`
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`
`TAI675.552 21m
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`
`ISBNIIISlIfiBII-SI] hum
`
`3130553252
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`

`

`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
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`xxiii
`
`I
`I
`I
`I
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`2
`2
`3
`4
`5
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`9
`9
`
`9
`t2
`[2
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`13
`17
`2|]
`2]
`2|
`22
`23
`23
`24
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`25
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`23
`2.9
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`viii
`
`CONTENTS
`
`34
`
`37
`3 E
`3"]
`39
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`45
`45
`45
`45
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`49
`5 l
`54
`54
`54
`56
`56
`57
`57
`59
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`61
`153-
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`67
`157
`63
`159
`'i'fl
`7‘0
`'32
`'i‘ 2
`
`Estimating Particle Densities of Materials for Use in the
`Dispersion Equations
`1.4 Coherence
`
`Temporal Coherence
`Spatial Coherence
`REFERENCES
`PROBLEMS
`
`SECTION 2. FUNDAMENTAL QUANTUM PROPERTIES OF LIGHT
`
`3 PARTICLE NATURE OF LIGHT — DISCRETE ENERGY LEVELS
`WERVIFW
`
`3.1 Bohr Theory til the Hydrogen Atom
`Historical Development of die Concept of Discrete Energy Levels
`Energy Levels of tlte Hydrogen Atom
`Frequency and Wavelength of Emission Lines
`Ionization Energies and Energy Levels of Ions
`Photons
`
`5.2 Quantum TheoryI of Atomic Energy Levels
`Wave Nature of Paro'cles
`
`Heisenberg Uncertainty Principle
`Wave Theory
`Wave Functions
`Quantum States
`The Schrodi nger Wave Equation
`Energy and Wave Function for the Ground State of the
`Hydrogen Atom
`Excited States onydrogen
`Allowed Quantum Numbers for Hydrogen Atom Wave Functions
`5.! Angular Momentum of Atoms
`Orbital Angular Momentum
`Spin Angular Momentum
`Total Angular Momentum
`3.4 Energy.I Levels Associated with Due-Electron Atoms
`Fine Structure ofSpectral Lines
`Pauli Exclusion Principle
`3.5 Periodic Table olthe Elements
`
`Quantum Conditions Associated with Multiple Electrons Attached
`to Nuclei
`
`Shorthand Notation for Electronic Configurations ofAtoms Having
`More Than Dne Electron
`
`3.6 Energy Levels nl' Mulli-Electron Atoms
`Energy-Level Designation for Multi-Electron States
`Russell—Saunders or L5 Coupling — Notation for Energy Levels
`Energy levels Associated with Two Electrons in Unfilled Shells
`Rules for Obtaining S: L. and J for L5 Coupling
`Degeneracy and Statistical Weights
`j—j Coupling
`Isoelectronic Scaling
`
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`

`

`Eli
`Eli
`
`89
`3'9
`
`94
`
`95
`'33
`lfll
`Hill
`
`103
`105
`106
`Hill—tr
`109
`109
`114
`115
`113
`12|
`122
`123
`124
`124
`
`125
`
`CONTENTS
`
`REFERENCES
`FEDELEMS
`
`ti RADIATNE TRANSITIDNS AND EMISSION LINEWIDTH
`D‘I'EIHI'IE'H'
`
`4.] Decay ofExcited States
`Radiative Decay of Excited States of Isolated Atoms —
`Spontaneous Emission
`Spontaneous Emission Decay Rate — Radiative Transition
`Probability
`Lil'eu'me of a Radiating Electron — The Electron as a Classical
`Radiating Harmonic Dscillator
`Nonradiative Decay of die Excited States — Collisional Decay
`4.1 Fmissiim Broadening and Linewidth Due to Radiative Decay
`Classical Emission Linetviddi of a Radiating Electron
`Natural Emission Linewidlh as Deduced by lQuantum Mechanics
`{Minimum Linievvidth]I
`4“! Additional Emission-Broadening Pmesses
`Broadening Due to Nonradiative tCollisionall Decay
`Broadening Due to Dephasing Collisions
`Amorphous Crystal Bmadening
`Doppler Broadening in Gases
`‘v'oigt Lineshape Profile
`Broadening in lEases Due to Isotope Shifts
`Comparison of 'v'alious Types of Emission Broadening
`1L4 Quantum Mechanics] Description of Radiating Atoms
`Electric Dipole Radiation
`Electric Dipole Marlin Element
`Electric Dipole Transition Ptobability
`Oscillator Strength
`Selection Rules for Electric Dipole Transitions Involving Atoms
`with a Single Electron in an Unfilled Subshell
`Selection Rules [or Radiative Transitions Involving Atoms with
`More Than l[.‘Ine Electron in an Unfilled Subshell
`
`Parity Selection Rule
`Inefficient Radiative Transitions — Electric Quadnipole and Ddter
`Higher-Order Transitions
`REFERENCES
`PROBLEMS
`
`S ENERGY LEVELS AND RADIATWE PROPERTIES OF MOLECULES.
`LIQUIDS. AND SOLIDS
`WERYIE'H'
`
`5.1 Molecular Energy Levels and Spectra
`Energy Levels of Molecules
`Classification of Simple Molecules
`Rotational Energy Levels of Linear Molecules
`Rotational Energy Levels of Symmetric—Top Molecules
`Selection Rules for Rotational Transitions
`
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`

`CONTENTS
`
`Vibrational Energy Levels
`Selection Rule for Vibrational Transitions
`Rotational—Vibrational Transitions
`Probabilities of Rotational and VIbrational Transitions
`
`Electronic Energy Levels of Molecules
`Electronic Transitions and Associated Selection Rules of
`Molecules
`Emission Line-width of Molecular Transitions
`
`The Franck—Condon Principle
`Escin'ier Energy Levels
`5.2 Liquid Energy Levels and Their Radiation Properties
`Structure of Dye Molecules
`Energy Levels of Dye Molecules
`Excitation and Emission of Dye Molecules
`Detrirnental Triplet States of Dye Molecules
`5.5 Energy Levels in Solids — Dielectric Laser Materials
`Host Materials
`
`Laser Species — Dopant Ions
`Narrow-Li newidlh Laser Materials
`Broadband Tunable Laser Materials
`
`Broadening Mechanism for Solid-State Lasers
`5.4 Energy Levels in Solids — Semiconductor Laser Materials
`Energy Bands in Crystalline Solids
`Energy Levels in Periodic Structures
`Energy Levels of Conductors. Insulators. and Semi conductors
`Excitation and Decay of Excited Energy Levels — Reoombinarion
`Radiation
`
`Direct and Indirect Bandgap Semiconductors
`Electron Distribution Function and Density of States in
`Semiconductors
`intrinsic Semiconductor Materials
`
`Extrinsic Semiconductor Mmerials — Doping
`p—n Juncli ons — Recombination Radiation Due to Electrical
`Excitation
`
`Heterojunction Semiconductor Materials
`Quantum 1Wells
`1t’ariation of Bandgap Energy and Radiation Wavelength will:
`Alloy Composition
`Recombination Radiation Transition Probability and Linewidlli
`REFERENCES
`PROBLEMS
`
`6 RADLATION AND THERMAL EQUILIBRIUM — ABSORPTION AND
`STIMULhTEI] EMISSION
`overwrew
`
`6.1 Equilibrium
`Thermal Equilibrium
`Thermal Equilibrium 1.iu Conduction and Convection
`Thermal Equilibrium yia Radiation
`
`143
`143
`144
`143
`149
`
`15D
`15D
`15!
`152
`153
`153
`155
`156
`15’:'
`153
`153
`159
`16!
`166
`163
`163
`163
`ITO
`172
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`1??-
`1714
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`175
`1'19
`1 79
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`132
`134
`136
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`19!
`195
`195
`195
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`199
`199
`199
`199
`2m
`2m
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`CONTENTS
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`6.1 Radiating Bodies
`Stefan—Boltzmann Law
`Wien‘s Law
`eradiance and Radiance
`
`6.3 Cavity Radiation
`Counting die Number ofCai-‘ity Modes
`Rayleigh—Jeans Formula
`Planck‘s Law for transit],r Radiation
`RelaLionship between {'a‘titj.r Radiation and Biankhody
`RadiaLion
`
`Wavelength Dependenoe of Biackbody Emission
`6.4 Absorption and Stimulated Eniisnon
`The Pn noiple ofDetailed Balance
`Absorption and Stimulated Emission Coefficients
`REFERENCES
`PROBLEMS
`
`SECTION 3. LASER AMPLIFIERS
`
`'1 EON DITICINS FOR PRODUCING A. LASER — POPULATION
`INVERSIGHS. GAIN. AND GAIN SATURATiGH
`OVERVIEW
`
`2.] Absorption and Cain
`Absorption and Gain on a Homogeneous!)I Broadened Radiau've
`Transition {Loren Eian Freouenc'j,r Distributioni
`Gain Coefficient and Stimulated Emission Cross Section for
`
`Homogeneous Broadening
`Absorption and Gain on an Inho mogeneousiy Broadeoed Radiative
`Transition {Doppler Broadening with a Gaussian Distributiont
`Gain Coefficient and Stimulated Emission Cross Section for
`
`Doppler Broadening
`SLau'sLicaI Weights and the lGain Equation
`Relationship of Gain Coelficient and Su'muiated Emission
`Cross Section to Absorption Coefficient and Absorption
`Cross Section
`
`2.2 Population Inversion thiecennary Condition [or a Laser!
`2.3 Salutation Intensity [Sufficient Condition for a Laser]
`2.4 Development and Gmwtli of a Laser Beam
`Growth of Beam for a Gain Medium with Homogeneous
`Broadening
`Shape or Geomeu'y of Amplifying Medium
`Growlh of Beam for Doppler Broadening
`2.5 Expimeutial Emil] Factor {Gain}
`2.6 Threshold Requirements for a Laser
`Laser with No Mirrors
`Laser with One Minor
`Laser with Two Mirrors
`REFERENCES
`PROBLEMS
`
`20]
`20-4
`205
`21315
`2D"?
`203
`209
`213
`
`211
`214
`215
`216
`21'?
`22|
`22]
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`225
`225
`225
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`225
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`229
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`23!]
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`23 |
`232
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`233
`234
`235
`233
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`233
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`24-9
`253
`253
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`

`xii
`
`CONTENTS
`
`255
`255
`255
`
`255
`
`256
`25][
`25”:r
`253
`253
`26!
`26!
`26!
`
`264
`
`266
`26”.:r
`263
`2'20
`2'22
`2'23-
`2'23
`2'26
`2'29
`2'29
`
`230
`232
`234
`234
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`233
`233
`
`290
`290
`
`2 2
`
`92
`293
`
`295
`293
`it]!
`304
`
`LASER OSCILLATION ABOVE THRESHOLD
`WERWEW
`3.} Laser Cain Saturation
`
`Rate Equations of the Laser Levels That Include Stimulated
`Emission
`
`Population Densities of Upper and Lower Laser Levels with
`Beam Present
`
`Small—Signal Gain Coefficient
`Saturation of Lhe Laser Gain above Threshold
`
`3.2 Laser Beam Growth beyond the Saturation Intensity
`Change from Exponential Ground: to Linear Growth
`Steady-3 taLe Laser IIIIBI'ISll)’
`3.3 Optimization oi' Laser Output Power
`Optimum Dulpllt Mirror Transmission
`Optimum Laser Dutput lntensit}l
`Estimating Optimum Laser {Jutput Power
`3.4 Energl.I Exchange between Upper Laser Level Population and
`Laser Photons
`
`Decay Time ofa Laser Beam I».II.-'itl'u'n an Dpfieal Cavity
`Basie Laser Cavity Rate Equau'ons
`Steady-S tate Solutions below Laser Threshold
`Steady—S Late flperali on above LaseI Threshold
`3.5 Laser Output Fluctuations
`Laser SpiIting
`Relaxation DsoiIIaLions
`
`3.6 Laser Amplifiem
`Basie Amplifier Uses
`Propagation of a High-Power. Short-Duration Optical Pulse through
`an Amplifier
`Saturation Energy Fluenoe
`Amplifying Long Laser Pulses
`Amplifying Short Laser Pulses
`Comparison ofEifioient Laser Amplifiers Based upon Fundamental
`Sarnrali on Limits
`
`Mirror Array and Resonator {Regenerative} Amplifiers
`REFERENCES
`PROBLEMS
`
`REQUIREMENTS FOR OBTAINING POPULATION INVERSIONS
`OVERVIEW
`
`9.1 Inversinns and Two-Level Systems
`9.2 Relative Decay.r Rates — Radiative versus Collisional
`9.3 Sleadvfitate Inversions in Three; and Four-Level Systems
`Three Level Laser widi die Intermediate Lave! as die Upper Laser
`Level
`
`Three-Level Laser said: the Upper Laser Level as the Highest Level
`Four-Level Laser
`
`9.4 Transient Population Invern'ons
`
`
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`

`CONTENTS
`
`xiii
`
`9.5 Processes That lnltiliit or Destroy Int'crsions
`Radiation Trapping in Atoms and Ions
`Electron Collisions] Themalizaflon of the Laser Levels in Atoms
`and Iona
`
`Comparison of Radiaflon Trapping and Electron Collisional Mixing
`in a Gas Laser
`
`Absorption within ll'IE Gain Medium
`REFERENCES
`rnosLsn-ls
`1G LASER PUMPING REQUIREMENTS AND TECHNIQUES
`CWER'IFIEW
`
`111.1 Excitation or Pumping Threshold Requirements
`111.1 Pumping Pathways
`Excitation by Direct Pumping
`Excitation by Indirect Pumping {Pump and Transfer}
`Specific Pump—and-Transfer Processes
`111.3- Spccific Excitation Parameters Associated 1i'rith
`Optical Pumping
`Pumpng Geometries
`Pumping Requirements
`A Simplified Optical Pumping Approximation
`Transverse Pumping
`End Pumping
`Diode Pumping of Solid—State Lasers
`Characlen Lotion ofa Laser Gain Medium with Dpli cal Pumping
`{Slope Efficiency)
`10.4 Specific Excitation Parameters Associated ‘I-‘Flll't
`Particle Pumping
`Electron Collisional Pumping
`Heavy Particle Pumping
`A More Accurate Description ofEJechon Excitation Rate to a
`Specific Energy Level in a Gas Discharge
`Electrical Pumping of Semiconductors
`REFERENCES
`reactants
`
`SEETICIN 4. LASER RESONATORS
`11
`LASER CAVITY MODES
`OVERVIEW
`11.1 Introduction
`
`11.1 Longitudinal Laser Cavity Modes
`Fabry—Perol Resonator
`Fabric—Perot Cavity Modes
`Longitudinal Laser Cavity.r Modes
`Longitudinal Mode Number
`Requirement: for the Development of Longitudinal
`Laser Modes
`
`30'?
`3-03
`
`31]
`
`315
`
`3-16
`319
`319
`322
`322
`
`322
`324
`324
`32'?
`3-30
`
`33‘?
`339
`342
`3-44
`346
`34E
`35E]
`
`3-52
`
`355
`355
`3-59
`
`359
`351
`353
`364
`
`3?]
`Bil
`3?]
`
`3-22
`3-32
`329
`381]
`3-81]
`
`382
`
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`

`xiv
`
`CONTENTS
`
`11.3 Transverse Laser Cavity Modes
`Fresnel—Kirchhoff Diffraction Integral Formula
`Development ol'Transverse Modes in a Cavity with Piano—Parallel
`Mirrors
`
`Transverse Modes Using Curved Mirrors
`Transverse Mode Spatial Distributions
`Transverse Mode Frequencies
`Gau man-Shaped Transverse Modes wimin and beyond the
`Laser Cavity
`11.4 Properties of Laser Modes
`Mode Characteristics
`Effect of Modes on die Gain Medium Profile
`REFERENCES
`PROBLEMS
`
`12 STABLE LASER RESONATORS AND GAUSSIAN BEAMS
`MERVIEH'
`11.1 Stable Curved Mirror Cavities
`Curved Mirror Cavities
`ASCD Matriees
`
`Cavity Stability Criteria
`11.1 Properties of Gaussian Beams
`Ptopagatim ofa Gaussian Beam
`Gaussian Beam Properties of Two-Mirror Laser Cavities
`Properties of Specific Two—Mirror Laser Cavities
`Mode 1Inl'olurne ofa Hermite—Gaussian Mode
`
`11.3 Properties of Real Laser Beams
`11.4 Propagation of Gaussian Beams Using ARCH Matrices —
`Complex Beam Parameter
`Complex. Beam Parameter Applied to a Two-Mirror Laser Cavity
`REFERENCES
`PRDBIJIMS
`
`13 SPECIAL LASER CA‘vflTlES AND CAVITY EFFECTS
`OVERVIEW
`13.1 Unstable Reslmaturs
`
`13.2 Q-Stvitehing
`General Desrnption
`Theory
`Methods of Producing Q—Switching within a Laser Cavity
`13.1 CajnaSwitehing
`13.4 Mode-Ioeliing
`General Desenplion
`Theory
`Ted'iniques for Producing Mode—Locking
`13.5 Pulse Shortening Techniques
`Self-Phase Modulation
`
`Pulse Shortening or Lengthening Using Group 1ir'eloeity Dispersion
`Pulse Compression {Shortening} with Gratings or Prisms
`Ultrashort-Pulse Laser and Amplifer System
`
`384
`385
`
`336
`390
`391
`392
`
`393-
`396
`396
`39Gr
`399
`399
`402
`492
`492
`402
`
`410
`4”
`412
`41']r
`42l
`413
`
`415
`423
`43 2
`43 2
`434
`434
`434
`439
`439
`44 l
`
`450
`45I
`45l
`45l
`456
`463
`4153
`
`415']r
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`

`

`CONTENTS
`
`[3.6 Ring Lasers
`Monolidric Unidirectional Single-Mode Hd:YAG Ring Laser
`Two—Mirror Ring Laser
`[3.1r Complex Beam Parameter Analys'fi Applied to Mimi-Mirror
`Laser Cavities
`
`Three—Mirror Ring Laser Canal}r
`Three— or Four—Mirror Focused {Savity
`[3.8 Cavities for Enduring Spectral Narrowing of
`Laser l[flutput
`Cavity.r with Additional Fabry—Perol Etan-n for Narrow—Frequency
`Selection
`
`Tunable \C'avit},I
`Broadband Tunable cw Ring Lasers
`Tunable {'avitj,r I'or LlItra.narrow-Frequent).r Dutput
`Dislributed Feedback (DFBJ Lasers
`D'islributed Bragg Reflection Lasers
`[3.'.?I Laser lCavities Requiring Small LDiameter Cain Regions —
`Astigmalir‘afly Compensated Cavities
`[3.10 Waveguide Cavities for Gas lasers
`REFERENCES
`ProaLI-zlus
`
`SECTION 5. SPECIFIC LhSER SYSTE M5
`
`14 LASER SYSTEMS INVOLVING LEW-DENSITY GAIN MEDIA
`OVERVIEW
`[4.1 Atomic Gas Lasers
`Introduction
`Helirmr—Neon LasH
`
`Gcneral Descri plion
`Laser Structure
`Excitation Mechanism
`
`Applications
`Argon Ion Laser
`General Descriplion
`Laser Structure
`Excitation Mechanism
`
`Kijrpton [on Laser
`Applications
`Heliluu—E'admium Laser
`
`General Descriplion
`Laser Structure
`Excitation Mechanism
`
`Applicau'ons
`Copper 1r'apoi' Laser
`General Descriplion
`Laser Structure
`Excitation Mechanism
`
`Applications
`
`453
`459
`4m
`
`4m
`
`are
`4?3
`
`47"8
`
`4?S
`
`HS
`480
`480
`4SI
`434
`
`484
`485
`486
`488
`
`49I
`4E"
`49I
`49I
`492
`
`492
`493
`494
`
`49'?
`49'?
`49?
`4913
`499
`
`500
`501
`5DI
`
`SDI
`502
`504
`
`505
`595
`505
`50'?
`50'?
`
`509
`
`
`
`
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`

`

`CONTENTS
`
`1-1.2 Molecular Cas Lasers
`Introduction
`Carbon Dioxide Laser
`
`General Descliption
`Laser Structure
`Excitation Mechanism
`
`Application:
`Euimer Lasers
`
`General Descnplion
`laser Structure
`Excitati on Mechanism
`
`Applications
`Nitrogen Laser
`General Descliption
`Laser Structure and Excitation Mechanism
`
`Applications
`Far-Infrared Gas Lasers
`
`General Desclipfion
`Laser Structure
`Excitation Mechanism
`
`Applications
`Chemical Lasers
`
`General Descliption
`Laser Structure
`Excitation Mechanism
`
`Applications
`14.3 K—Ray Plasma lasers
`Introduction
`
`Pumping Energy Requirements
`Excitation Mechanism
`
`Optical Casiu'es
`X—Ray Laser Transitions
`Applications
`14.4 FreeLElectmn laser's
`Introduction
`Laser Structure
`
`Applications
`EEFERENE‘ES
`
`15 LASER SYSTEMS INVOLVING HIGH—DENSII’Y GAIN MEDIA
`ovcswsw
`
`'ISJ flrganic Dye Lasers
`Introduction
`Laser Structure
`Excitation Mechanism
`
`Application:
`15.2 Solid-Statelasers
`Introduction
`
`5113
`510
`51 I
`
`5] |
`5| I
`5 I5
`
`5 I5
`5115
`
`5115
`5 IT
`513
`
`5213
`52!]
`521]
`521
`
`522
`522
`
`522
`523
`523
`
`524
`524
`
`524
`524
`524
`
`525
`525
`525
`
`525
`523
`
`532
`532
`532
`535
`535
`5345
`
`537r
`53?
`
`539
`539
`
`539
`539
`54-0
`543
`
`544
`545
`545
`
`
`
`
`
`
`
`

`

`CONTENTS
`
`xvii
`
`Ruby Laser
`General Description
`Laser Structure
`Etci tation Mechanism
`
`Applications
`Neodymium VAC and Class Losers
`General Description
`Laser Structure
`Excitation Mechanism
`
`Applications
`Neodymiumfl'LF Lasers
`General Description
`Laser Structure
`Etci lation Mechanism
`
`Applications
`Neodymiumfl'flrium Vasiudatc I Ndf’i’Vflq} Lasers
`General Description
`Laser Structure
`Etci tation Mechanism
`
`Applications
`Ylierbiumz'YAG Lasers
`
`General Description
`Laser Structure
`Esci lation Mechanism
`
`Applications
`Alcxandrile laser
`
`General Description
`Laser Structure
`Excitation Mechanism
`
`Applications
`Titanium Sapphire Laser
`General Description
`Laser Structure
`Etci lation Mechanism
`
`Applications
`Chromium IliS AF and LiCAF Lasers
`
`General Description
`Laser Structure
`Etci tation Mechanism
`
`Applications
`Fiber Lasers
`
`General Description
`Laser Structure
`Etci tation Mechanism
`
`Applications
`Color Gunter lasers
`
`General Description
`Laser Structure
`
`54'?
`54'?
`
`549
`55!]
`55!]
`55I
`553
`554
`555
`555
`5515
`5515
`55'?
`55?
`55'?
`55'?
`558
`558
`559
`55’?]I
`550
`55%]
`55]
`552
`552
`553
`553
`554
`555
`555
`555
`55'?
`553
`55E
`55E
`558
`559
`5?D
`5?D
`5m
`5?I
`5?I
`51"2
`5?3
`5?3
`5?4
`
`
`
`
`
`
`
`

`

`xviii
`
`CONTENTS
`
`Excitation Mechanism
`
`Applications
`ISJ Semimnductlw Diode Lasers
`Introduction
`
`Four Basie Types of Laser Materials
`Laser Structure
`
`Frequency Control of Laser {Jutput
`Quantum Cascade Lasers
`p—Dopecl Germanium Lasers
`Excitation Mechanism
`
`Applications
`REFERENCES
`
`SECTION :6. FFIEIZIIJENIE‘Ir MULTIPLICATlON OF LASER BEAMS
`16 FREOUEI'iIID'Ir MULTIPLICATlOH OF LASERS AND OTHER
`NONLINEAR OPTICAL EFFECTS
`OVERVIEW
`
`$6.1 Ware Pmpagalioll in an Anisotropic Crystal
`“5.2 Polarization Response of Materials to Light
`16.3 Secondaflrder Nonlinear Optical Processes
`Second Harmonic Generation
`
`Sum and Difference l-Treouentfii.r Generation
`Optical Parametric Oscillation
`16.4 Third-Order Nonlinear Dptica] Processes
`Third Harmonic Generation
`
`Intensity-Dependent Refi'actise Index — Self-Focusing
`16.5 Nonlinear Optical Materials
`“5.6 Phase Matching
`Description ofPhase Matching
`Achieving Phase Matching
`Types of Phase Matching
`16.? Saturahle Absorption
`16.8 Two-Photon Absorption
`16.9 Stimulated Raman Scattering
`16.1“ Harmonic Generation in Cases
`REFERENCES
`
`Appendix
`Index
`
`574
`5715
`5715
`5145
`519
`53!
`59!
`5'92
`594
`594
`596
`59?
`
`5o:
`oi]!
`60!
`603
`604
`
`695
`60?
`so?
`ECIE
`609
`till]
`till]
`tilt]
`6|?-
`6|5
`filS
`6|?
`SIB
`6|?
`6|?
`
`521
`625
`
`
`
`
`
`
`
`

`

`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
`
`
`
`
`
`
`
`

`

`INTRODUCTION
`
`Optical resonator or cavity
`A
`
`Ampllty'mg medium
`
`
`
`Figure 1-1 Simplified
`scl'tem atic oltypical laser
`
`Fully reflecting
`mirror
`
`Parllally transmitting
`mirror
`
`lasers} that is usually provided by mine-rs. Thus, in its simplest form, 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-].
`
`SIM PIJCl'l'Y OF A LASER
`
`The simplicity ofa laser can be understood by considering the light from acandle.
`Normally, a burning candle radiates light in all directions, and therefore illumi-
`nates 1various objects equally if they are equidistant from the candle. A laser lattes
`light that would normally 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 acandle were concentrated into a single beam of the diameter of the
`pupil of your eye (approximately 3 mm}, and if you were standing :1 distance of
`I In from the candle, then the light intensity would be 1,000,011 times as bright as
`the light that you normally see radiating from the candle! That is essentially the
`underlying concept efthe operation of a laser. However. acandle is not the kind of
`medium that produces amplification, and thus there are no candle lasers. ll lattes
`relatively special conditions within the laser medium for amplification to occur,
`but it is that capability oftaking light that would normally radiate from a source in
`all directions — and concentrating that light into a beam uavcling in a single direc-
`tion — that is involved in melting a laser. These special conditions, and the media
`within which they are produced, will be described in some detail in this took.
`
`UNIQUE PROPER'HES OF A LASER
`
`The beam of light generated by a typical lasercan 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 more restrictive than the values for many common
`light sources. We never use lasers for street illumination, or for illumination within
`our houses. We don't use them for searchlights or flashlights or as headlights in
`
`
`
`
`
`
`
`

`

`INTRODUCTION
`
`our cars. Lasers generally have a narrower frequency distribution. or much higher
`intensity. or a much greater degree of collimation. or much shorter pulse duration.
`than that available from more common types of light sources. Therefore. we do use
`them in compact disc players, in supermarket check—out scanners. in surveying in—
`stru meets. and in medical applications as a surgical knife or for welding detached
`retinas. We also use them in communications systems and in radar and military.r
`targeting applications. as well as many other areas. A laser is a specialized light
`source that should he used only when ire unique properties are required.
`
`THE LASER SPECTRUM AND WAVELENGTI'IS
`
`A portion ofthe electromagnetic radiation spectrum is shown in Flgure 1—2 for the
`region covered by currently existing lasers Such lasers span the wavelength range
`from the farinfrared part of the spectrum (.1. = LOGO urn) to the soft—X—ray region
`[It = 3 nm).. thereby covering a range of wavelengths of almost six orders ol'rnag—
`nitude. There are several types of units that are used to define laser wavelengths.
`These range from micrometers orrnicrons (urn) in the infrared to nanometers trim)
`and angstroms {eat} in the visible. ultraviolet {UV }. vacuum ultraviolet {VLTV ]. ex—
`treme ultraviolet {EUV' or XUV }, and soft—X—ray {SXR} spectral regions.
`
`WAVELENGTH UHI'I'S
`
`lum = 10—6 m;
`In: Hr“:I m:
`1nn1= 10-9 If.)
`
`Consequently, I micron turn} : IDJDED angstroms [fit] 2 1.000 nanometers t’nm}.
`For example. green light has a wavelength of 5 x llII'I m = 115 um = 5.000 it =
`500 nm.
`
`Figue- 1—1 Wavelength
`ran-go ofva‘ieus lasers
`
`CD
`
`4.
`
`
`
`Ar..
`
`.—
`
`FIRtasnr:
`a. .
`..
`..
`.-
`
`I
`
`I
`
`CD‘.
`
`Hue-Fla
`
`Fell Infrared
`
`Inhaled
`
`N:
`Rub'p'
`KI'F
`Hat-Ne
`MINI“?
`Ho Ca
`
`Sow-Flag.-
`users
`-
`_
`_-
`
`Erwin: Dru
`1131293
`Wis-baa
`
`an
`Ulravnlel
`
`SH“ ill Ray:
`
`
`
`J‘-
`
`-——-- ENERGY {27“}-
`
`..
`
`
`
`
`
`
`
`

`

`INTRODUCTEON
`
`WAVELENGTH REGIONS
`
`Far infrared: ID to [.000 um;
`middIe infrared: Ito It] itrn;
`near infrared: 0.? to 1;.im'r
`visible: [14 to [17 am. or 401110 1"th nrn:
`ultraviolet: 0.2 to Ild rim. or EDD to 490 rim:
`vacuum ultraviolet: 0.] to 0.2 rim. or 100 to 201] rim:
`extreme ultraviolet:
`It] to 100 nm‘,
`soft X—rays:
`I nm to approiiirnatelyr 20—30 am {some overlap with ELFV}.
`
`A. BRIEF HISTORY OF 11'IE LASER
`
`Charles Townes took advantage of the stimulated emission process to construct a
`microwave amplifier, referred to as a eraser. 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 wavelengths produced in the maser were compara—
`ble to the dimensions of the device. so extrapolation to the optical regime — wl'iere
`wavelengths were five orders ofmagnitude smaller— was not an obvious extension
`of that work.
`
`In 1958, Townes and Schawlow published a paper concerning theirideas about
`extending the mas-er concept to optical frequencies. Theyr developed the concept
`of an optical amplifier sin-rounded by an optical mirror resonant cavity to allow for
`growth of the beam. Townes and Schawlow each received a Nobel Prize for his
`work in this field.
`
`In 19150. Theodore Maimau of Hughes Research Laboratories produced the
`first Iaser using a ruby crystal as the amplifier and a fiashlamp as the energy source.
`The helical flashlarnp surrounded a rod—shaped ruby crystal, and the optical cavity
`was formed by coating the flattened ends of the ruby rod with a highly reflecting
`material. An intense red beam was observed to emerge from the end of the rod
`when the fiashlamp was fired!
`The first gas laser was developed in IQfiI by A. Javan, W. Bennett. and D. Har-
`riott of Bell Laboratories. using a mixture of helium arid neon gases. At the same
`laboratories. L. F. Johnson and K. Nassau demonstrated the first neodymium laser,
`which hassince becomeoneofthe mostreliable lasers available. This was followed
`
`in 1962 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 dioxide laser. which is one ofthe most efficient and
`powerful lasers available today. Later that same year. E. Bell of Spectra Physics
`discovered the first ion laser. in mercury vapor. [n I964 W. Bridges of Hughes Re-
`search Laboratories discovered the argon ion laser. and in I966 W. Silfvast. G. R.
`Fowles. and B. D. Hopkins produced the first blue helium—cadmium metal vapor
`
`
`
`
`
`
`
`

`

`INTRODUCTION
`
`laser. During that same year. P. P. Sorolcin and .l. R. Lardtard of the IBM Research
`Laboratories developed the first liquid laser using an organic dye dissolved in a sol-
`vent. thereby leading to the category of broadly tunable lasers. Also at that time.
`W. Walter and eo—worlters at TRG reported the first copper vapor laser.
`The first vacuum ultraviolet laser was reported to occur in molecular hydro-
`gen by R. Hodgson of IBM and independently by R. Waynant et al. of The Naval
`Research Lab-oratoties in 1970. The first of the well-known rare-gas—halidc ex-
`cin'ter lasers was observed in xenon fluoride by I. .l. Ewing and C. Brau of the
`Avco—Everett Research Laboratory in I'S‘TS. In that sarrte year, tl'te first quantum-
`well laser was made in a gallium arsenide semiconductor by J. van der Ziel and
`co-worlters at Bell Laboratories. In 19'36. .l. M. .l. l’vladey and co-worlrers at Stan-
`ford University demonstrated the first free-electron Iaseramplifier operating in the
`infrared at the C03 laser wavelength. In I'Ji'g. Walling and co-worlters at Allied
`ChemicalCorporation obtained broadly tunable laser ourputfmma solid-stale laser
`material called alexandrite. and in “3'85 the first soft—X—ray laser was successfully
`demonstrated in a highly ionized selenium plasma by D. Matthews and a largenum-
`ber of co—worlters at the Lawrence Livermore Laboratories. [n 1936. P. Moulton
`discovered the titanium sapphire laser. In I991, M. Hasse and co-worltcrs devel-
`oped Ihe first blue—green diode laser in ZnSe. [11 I994, F. Capasso and co—worlters
`developed the quantum cascade laser. In 1996, S. Nahamura developed the first
`blue diode laser in GaN—based materials.
`In l9fil. Fox and Li described the existence of resonant transverse modes in
`
`a laser cavity. That same year. Boyd and Gordon obtained solutions of the wave
`equation for confocal resonator modes. Unstable resonators were demonstrated
`in l9l59 by Empire and Sooy and were described theoretically by Siegman. Q-
`switching was first obtained by McClung and Hellwarth in WISE and described
`later by 1Wagner and Lengyel. The first mode-locking was obtained by Hargmve.
`Fork. and Pollack in [964. Since then, many special cavity arrangements, feedback
`schemes. and otherdevices have been developed to improve the control. operation.
`and reliability of lasers.
`
`OVERVIEW OF THE BOOK
`
`Isaac Newton described light as small bodies emitted from shining substances.
`This view was no doubt influenced by the fact that light appears to propagate in a
`straight line. Clo-i stian Huygens. on the other hand. described light as a wave mo-
`tion in which a small source spreads out in all directions: most observed effects —
`including diffraction, reflection. and refraction — can be attributed to the expansion
`ofprimary waves and of secondary wavelets. The dual nature of light is still a use—
`ful concept. whereby the choice of particle or wave explanation depends upon the
`effect to be considered.
`
`Section fine of this book deals with the fundamental wow properties of light1
`including Maxwell's equations. the interaction of electromagnetic radiation with
`
`
`
`
`
`
`
`

`

`INTRODUCTFUN
`
`matter, absorption and dispersion._ and coherence. Section Two deals with the fun-
`damental quantum properties of light. Chapter 3 describes the concept ofdiscrete
`energy levels in atomic laser spmies and also how the periodic table of the ele-
`ments evolved. Chapter 4 deals with radiative transilions and emission linewidths
`and the probability of making transitions belween eneng}l levels. Chapter 5 con-
`siders energy levels of lasers in molecules liquids. and solids — both dielectric
`solids and semiconductors. Chapter I5 lhen considers radiation in equilibrium and
`Ihe concepts of ab