LASER FUNDAMENTALS
`
`SECOND EDITION
`
`WILLIAM T. SI LFVAST
`
`School ul Oplics 1' CRECIL
`Lhiunlsily of Centrd Florida
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`CAMBRIDGE
`UNIVERSITY PRESS
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`ASML 1510
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`ASML 1510
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`PUBLISHED III" THE 3% 51"N'lII].|l'l'E OF THE. UNIVERSITY DIFCALIBEJIIIE
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`ISBN l]—32l—333-15-!)
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`
`Contents
`
`Prefiice to the Second .E'dition
`
`Prefixce to the First Edition
`
`Aeknawletflgnlttents
`
`1
`
`INTRODUCTION
`UI"EIl\I'IE|I'
`llttmtltlclion
`Deliilion of llie I..ase-1'
`
`Simplicily 0|’ 2 Laser
`Unitpe
`of :1 Laser
`The Laser Spectrum and Hfawlertgtlls
`A Brief Hislory ofllle Laser
`f|1reI't"IeIrIr of the ll‘-uolt
`
`SECTION 1- FUNDAMENTAL WAVE PROPERTIES OF LIGHT
`
`2 WAVE NATURE OF LIGHT — THE INTERACTION CIF LIGHT
`WITH MATERIALS
`CW'Ell\iIEH'
`
`2.1 Ma!n'rI.=Il"s Faplatiuns
`2.1 IL'[a:n-nell"s Wave Equulinns
`Maxwell's ‘Wave Equations for a Vacuum
`Solution of tho Gentztal Wave Equation — Equivalsooo of Light and
`EI c Radiation
`‘Wave VeIot::il].r — ]3'I1aat'. and Group Velocities
`tkttetalized So-Iulion ofdmwatre Equation
`TI.'aI'IS‘W:l'Sl.'. Eloclrolttagoatic Waves and Polarized Light
`Flow of EI ic Energy
`Radiation [mm a Point Souroo (Elocuic Dipole Radiation]
`2.3- [ute:nu:lioI1 of Flleclrutlagnelic Radialion tliglit) will Matter
`Spread of Light in a Medium
`Maxwell‘: Equations in a Medium
`Application of Maxwell's Equations In Dielectric Materials —
`Laser Gain Media
`
`Complex: Index of Rofmclzion — Optical Constants
`Absorption and Dispersion
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`page xix
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`ui
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`xxiii
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`L11-H-'4-'lI‘-'lI‘-'l'—'—-'—
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`EHEEfifitfii-"BEESEfiuauaua
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`CIIIITEHTS
`
`Estimating P-rrticle Densities ofllllaterials {or Use in the
`Dispersion Equations
`LII Coherenre
`
`Ternporal Coherence
`Spatial Coherence
`IEFEIENCE
`PIIIIILEMS
`
`SECTION 2. FUHDAHENTAL I'1U.Al|lTl.|II PROPERTIES OF LISHT
`
`3 HARTICLE NATURE OF LIGHT — DISCRETE ENERGY LEVELS
`{I'I"EE'I"lE'H"
`
`3.] Bohr Theory olthe Hydrogen Atom
`Historical Detreloprznmt of the Concept of Di.screte Energ].r Levels
`Energy I..El|'ElS of the Hydrogen Atom
`Frequency and. Wavelength oi'EnIission Lines
`Ionization Energies and Energy levels of Ions
`Photons
`
`3.1 Quaiurn 'l'IIeo1'y ofA.toIrn'r Fnergy Levels
`Wave Nature of Particles
`
`Heisenberg Uncertainty Principle
`Wa1.re'l'l1eor}r
`Wave Rrnclions
`Uuanturn States
`The Schrodinger Wave Equation
`Energy and. Wave Rrncliort for the Ground State of the
`Hydrogen Atom
`Excited. States of Hydrogen
`Allowed Quanturn Numbers for Hydrogen Atomwave Functions
`3.! Angular Monlenltil of Alums
`Orbital Angular lt'Ior:nenIr.rrn
`Spin Angulx Momertotnr
`Total Angular Mourm
`LII Fnergy Letreh Afitrialrd with Due-Electron Atoms
`Fine Smrcture ol'Spectral Lines
`Pauli Exclusion Principle
`J5 Periodir: Title ol‘ the Elements
`
`'I;luanIurn Conditions Associated with Multiple Electrons Attached
`to Nuclei
`
`Shortltartd Notation for Electronic Configurations ol'Atorns Having
`More Than Clne EIect.ron
`
`3.6 Farergy Leveh 0|’ l"|-Itlli-Fleelron Atoru
`Energy-I.etrel Designation for Mulli-Electron States
`Russe|l—Sauntlers or L5‘ Coupling — Notation t'orEnerg3- Levels
`Energy Levels Associated with Two Electrons in Unlilled Shells
`Rules for Obtaining S, L, and J‘ for L5 Coupling
`Degerterac_',r and Statistical Weights
`fflmflm
`Isoelentronic Scaling
`
`EEEEER
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`EfiffifififlflfiEdfl33$Efl$EE9
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`ODHTHITS
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`nemnurces
`tltmnmms
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`-II RADIATNE TIIAIISITDNS AND EMISSION LINEWIDTH
`ovemrlcw
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`41:1 Decay ol'F.:t:t:itcd States
`Radiative Decay o1'E:rc:ited States of kolatearl Atoms —
`Spontaneous Enlission
`Spontaneous Ernission Decay Rate — Radiative Transition
`Probability
`l_il'etime I1l'a Radiating Electron — The Electron as a Classic.‘-ll
`Radiating Harmonic flscillator
`Nonradiative Deazay of the Excital States — Collisional Decay
`-1.2 Fartimion Broadening and Iinewidfll Due to
`Decay
`Clical Ernission l..inewidth of a Radiating Electron
`Natiual Emission l..inewidIh as Derluoed by Quantum Mechanics
`[Minimurn l..irtenridth)
`-1.3 Additional Faiissionsllroadening Processes
`Broadening Due to Nonradiati1pe(ColIisionaI) Decay
`Broadening Due to Dephasing Collisions
`Amorphous Crystal Brcrarlening
`Doppler Broadening in Gases
`Voigt Lihape Profile
`Broadening in Gases Due to Isotope Shifts
`Comparison of Various Types oIEmi$ion Broadening
`-1.4 -Quanlui Mechanical Description of RadiatingAtoms
`Electric Dipole Radiation
`Electric Dipole ltI'lan'i:r. Element
`Electric Dipole Transition Probability
`Oscillator Strength
`Selection Rules {or Electric Dipole Transitions lmnoliring Atoms
`with a Single Electron in an Unlilled Subshell
`Selection Rules for Radiative Transitions Involving Atoms with
`More Than One Elect.ron in an Unlilled Subshell
`
`Parity Selection Rule
`[neflicient Iladiative TI!2l.IEEllZll2l'.'E — Electric Quadrupole and Other
`Higher-Order Transitions
`nemnurces
`PROBLEMS
`
`5 ENERGY LEVELS AND RAEIATWE PROPERTIES OF MOLECULES.
`LIEIUIDS. AND SOLIDS
`ovemrlcw
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`5.1 Molecular Energy Inwels and Speclm
`Energjr Levels of Molecules
`Clmsificatinn of Sirrple Molecules
`Rotational Energy Levels o1'l..irtear Molecules
`Rotational Energy Levels oi Symmetric-Top Molecules
`Selection Rules {or Rotational Transitions
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`SIS
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`CCIITENTS
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`li"ibrationaJ Energy Levels
`S-election Rule for Vibrational Ttamilions
`Rr|tational—‘1"ibrational Transitions
`Probabilities ofRotar.ional and ‘lI'ibra1ionaIT|:ansciI:ions
`
`Electronic Energy Levels of Molecules
`Electronic Transitions and Associated Selection Rules of
`Molecules
`Emission Linewidlh ofldlolecular Transitions
`
`'l11e Franck—Condon Principle
`E'.u::imerEnetgy I..eI.rels
`5.2 liquid Enl.-rgy law:-B and Their
`Structure of Dye Molecules
`Energy Levels of Dye Molecules
`Exccitajion and Emission of Dye Molecules.
`Detrimenta] Triplet States ofDye Molecules
`5.3 Fanargy Lewls in S-oIds— Dielectric Lmcr Malerifls
`Host lulaterials
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`Properties
`
`Laser Speccies — Dopant Ions
`hlar1'r:n.Ia-I_.ine1n.ridIt| laser Materials
`Broadband Tumble Lmer Materials
`
`Broadening Mechanism for Solid—StaIJe Lasers
`541 Fan.-rgy Lewis in S-oIds— Sellitondnrlor Laser Materiah
`Energy Bands in Crystalline Solids
`Energy Levels in Periodic St|:ucIu|:es
`Energy I..eI|.rels offlomzluctors. Insulators. and S-emioomluctors
`Emeitarion and Decay oI'En:iIed Energy Levels — Recombination
`Radiation
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`Direct and Indirect Eandgap Semiconductors
`Election Disuibulzion Function and Density of States in
`Semiconductors
`Inuinsic Selniconrluctor Materials
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`Extrinsic Semiconductor Materials — Doping
`p—n Junctions — Recombination Radiation Due to Electrical
`Excitation
`
`I-Ieterojunclion Semtoo‘nduotor Matarials
`Quantum Wells
`"I"aI:iation of Eandgap Energy and Radiation ‘Wavelength with
`Alloy Composition
`Recombination Radiation Transition Probability and Linewirllh
`IEFEIENCE
`f‘IlJllI..EI'I'S
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`-I5 RADIATION All} THERMAL EQUILIBRIUM — ABSORPTION AND
`SIIMULATED EMISSIJN
`lII'|'I'.E’I"lE‘W
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`6.] F..|]II2llZl.IJ'I'l.I.I'I
`'l11erma| Equilibrium
`Tltermal Equilibrium via Comzluclion and Convection
`Thermal Equilibrium via Radiation
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`CON'I'EITS
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`6.2 Radiating Bodies
`Ste:fan—BoII1n1ann Law
`Wien‘s l..aw
`[rradiamce and Radiance
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`6.3 Cavity Radiation
`Counting the Nulnherofflauity Modes
`Ra].rIeigh—Jeans Fornurla
`Planck's law for Cavity Radiation
`Relationship between Cavity Radiation and Blackbndy
`Radiation
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`Wavelerrglh Degnndenoe of Blackbody Emission
`6.4 Absorption and Stimulated F.m%on
`The Principle ofDeta.iled. Balance
`Absorption and Stimulated Emission Cnefliccients
`EEFEBECES
`PROBLEMS
`
`SECFIDH 1. LASER AHPLIFIE
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`'.I' CONDITIONS FOR PROEIJEING A LASER — PDPIJ LATIDN
`I GAIN. AND GAIN SATURATION
`C|'I"El'r|'III’rI'
`
`1] Absorption and Cain
`Absorption and Gain on a Horznogeneouslj Broatlened. Radiative
`Transition (Lorentcian Frequency Distrilzlution}
`Crain Cnecllicient and Stimulated. Emission Cross Section for
`
`Homogeneous Broadening
`Absorption and Gain on an InhomogerIetI.1sI}r Broatlened Radi.ati1.re
`Transition (Doppler Broadening with a Gaussian Distribution}
`Gain Coetflicient and Stimulated. Emission Cross Section for
`
`Doppler Brnaderting
`Statistical Weights and the Gain Equation
`Relationship of Gain Co-e:lfit:ient and Stimulated Emimion
`Cross Section tofihsorption Coefliccient and Absorption
`Cross Section
`
`12 Population Inversion I Non-Err} Condition [or a Ilmr.-r]
`13 Salutation lntemitgr ifitlffirienl Condition for a Laser}
`'.-‘.4 Ilntloprnent and Crowtll of a Laser Beam
`Growth ofliléeam for a Gain Medium with Horznogeneous
`Broadening
`Shape or Geometry offitmplifiring Medium
`Growth ofliléeam for Doppler Broadening
`1.5 Exponential Crovwlll Factor {Gin}
`'.r'.I‘i Threshold Reqtlirfllents for a Laser
`Laser with No Minors
`Laser with flne Minor
`Laser with Two Mirrors
`B‘.E.F'EE$'CES
`PROBLEMS
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`2l]
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`CIIITENTS
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`B LASER OSEILLATION ABOVE Tl-IIESHOLD
`{I'|'EE‘I"lE'H'
`8.] Iaaer Cain Saturation
`
`Rate Equations ofthe Laser l_£‘I|'Etl.5 That lnolude Stimulated
`Emission
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`Population Densities of Upper and LowerLaser Levels with
`Beam Present
`
`S|nal|—Signal Gain Coefficient
`Saotration ofthe Laser Gain above Threshold
`
`5.2 Laser BIE".l]l‘t Crnrwtll hcgtroml the S-alnralinn Ir|ter|fi't}'
`Change from Exponential Growth to Linear GI:owIh
`Steady-State Laser Intensity
`IL! Oplimmtion of Laser Output Power
`Optimum Output Minor Transmission
`Optimum Laser Output Intensity
`Estimating Optimum l..aserOutput Power
`FM Fnergy Exellartge Ilelween Upper Laser I..-wel Population and
`Laser Plmlsons
`
`Decay Time ofa Laser Beam within an Optical Ca1I.Iit_',r
`Basic LaserCat.Iit}r Rate Equations
`Steady-State Solutions below l..aserTl:treshold
`Stead3r—State Operation ahove Laser'[lnreshold
`85 Laser Onlpli Flnctualiulis
`Laser Spilcing
`Relaxation Oscillations
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`8.6 laser.-lntpliliers
`Basic Amplifier Uses
`Propagption ofa High-Power, Short—DuI:ation Optical Pulse through
`an Amplifier
`Saturation Energy Fluenoe
`Amplifying Long Laser Pulses
`Amplifying Short Laser Pulses
`Comparison ofEffieient Laser Antpliliers Based upon l-"undalznental
`Saturation limits
`
`Minor Array and Resonator (Reget1erative)Ampliliers
`IEFEIENCE
`Il:lIlIll.El.[S
`
`9 REOUIREMEIITS FOR OETAINIHE POPULATION INVERSIOHS
`{I'|'EI"I"lE'W
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`9.] lII're1's'|ons and Two-Ia.-rel Systems
`9.2 Relative Decay Hales —
`versus Collisional
`‘L3 Steady-Slate Imrersions in TI1ree- and Four-I_.ewI Syst-ens
`Tlu:ee-Level Laser with the Ittl.-EI'I1I.'£ll3lE'. level as the Upper Laser
`Level
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`Tltree-Level Laser with the UpperI_aser I..e1.rel as the Highest level
`Four-level Laser
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`9.41 Transient Population lmrertinns
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`ODH'I'HITS-
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`9.5 Processes Thal lnhilait orflcstrny Intersions
`Radi:1ionTrapping in Atoms and Inns
`Electron Collisional Thetmalization of the 1.aserLevels in Atoms
`and lons
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`Comparison of Radiation Trapping and I-Electron Collisional Mixing
`in a Gas Laser
`
`Absorption within the Gain Medium
`REFERENCES
`FIIDILEHIS
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`10 LASER PI.IlhI3ING REQUIREMENTS AND TECI-INIOUES
`D‘I'EK‘|'IE.'I|l'
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`10.1 F.J£'C‘11fl1il2I'I or P'1lIp'IIgTl1rcsIJoId Requirements
`10.2 Ptmlping P'alI|1tIa3.'s
`Excitation by Direct Pumping
`Excitation by Indirect Pumping (Pump and Transfer]
`Specific Pump-and—Tran31'er Processes
`10.3 Specific Extilalion Parameters Ago-t:'|alc~d with
`Dptital Ptmtping
`
`Pumping Requirements
`A Simplified Optical Pumpcing Approximation
`Tf3.ll3l"E.l'S-B Pumping
`End Pumping
`Diode Pumping of Solid—SIale Lasers
`Cltatacletization ofa 1.aserG-ain Medium with flplical Pumping
`{Slope EFficienc)r]
`10.4 Specific Extilalion Parameters Assn-t:'tale~d with
`I"arIi'J:le Ptmtping
`Electron Collisional Pumping
`Heavy Panicle Pumping
`A lulorefitocurate Description ofElectn:tn Excitation Rate to a
`Specific Energy Leltrel in a Gas Discharge
`Elect'.rical Pumping ofsemiconduclors
`REFERENCES
`FIIDILEMS
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`SECFIDH II. LASER RESONATORS
`11 LASER EAMTY MODES
`D‘I'E.I‘|"IE.'I|"
`11.1 Introduction
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`11.2 I.-ucngiudirtal Laser Carly Monks
`Fal:tr]r—Pernl Resonator
`Fal:tr3r—Pemt Cavity Modes
`Longintdinal Laserflavity Modes
`Longintdinal lt'IodJe Number
`Requirements {or the Development ocI'Long;itudina]
`Laser Modes
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`Z’-ll
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`3llS
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`CCIITEHTS
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`I 1.3 Tralsverse Laser Caviy Modes
`l-'-'resnel—Kirchhofl' Diflraction Integral Formula
`Developroent o1'Transverse Modes in aCavil}' vrirlr Plane-Parallel
`Mirrors
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`Transverse Modes Using Curved. Mirrctrs
`Transverse Mode Spatial Distributions
`Transverse Mode Frequencies
`Gaussian-Shaped Transverse Modes vrirlrin and beyond the
`Laser Cavity
`I Lil Properlies of Imer Modes
`Mode Characteristics
`Effect. of Modes on the Gain Medium Profile
`REFERENCES
`FRDIIEMS
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`12 STABLE LASER RESDIIATDRS Jul-ID GJLUSSIAN BEAMS
`fl‘|’I'.R"r"lE’rI'
`I1] Stable Crnvrd h'[i11'or
`Curved. Minor Cavities
`AHCD Matrices
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`Cavit_-,r Stability Criteria
`I12 Properlies ocf Gumian BE".l]II'l£
`Propagation of a Gaussian Bea.rn
`Crsrrssian Beam Pnaperties ofTvvo-Minor LaserCavir.ies
`Properties offlpecilic Tvtro-Mirror Lmer Cavities
`Mode Volume cufa Hern1iIe—IGar.1ssian Mode
`
`ocf Real Laser Beans
`IL!
`ILII Propagation offlarmsial ll‘-earns Usingflflflfl Matrices-
`Complex Heal Plaranrcler
`Complex Bea.nr Parameter Applied to a Trrvo-Mirrctr LaserCavit]r
`REFERENCES
`FIOILEMS
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`13 SI3EEl.r'4rL LASER GPHITIES AND CAVITY EFFECTS
`0‘|"E|l'I|'lEH'
`I3.l Ulflable Resonflors
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`13.2 Q-Svrilclling
`General Description
`Tlieorjr
`Methods c-fPrcId.uc:ing Q-Svritching within a 1.aserCavit3r
`LL! Ca'n—S'nIitc1Iing
`I341 Morlr.--Loclring
`General Description
`Theorjr
`Techniques for Producing Mode—Loc|:ing
`I35 Pulse 5IIorItningTecIII'qne-s
`Sell-Phase Modulation
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`Pulse Shortening or Lengthening Using Group Velocity Dispersion
`Pulse Coropression [Shomerring] with Gratings or Prisms
`Ultrashort-Pulse Laserand Arrzplifer Sjs-tent
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`-1-2|
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`-1-18
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`ODHTHITS
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`I16 Ring Lasers
`Monolithic Unidirecliottal Single-Mode l"Id:YAG Ring Laser
`T1nro—Mi|:1'or Ring Laser
`I1? Complex Beam Parameter Analysis Applied to Iiltlti-Mirror
`EM Cavilie-s
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`Three-Mirror Ring Laser Cavity
`TllIEB— or Four—lIlin'or FcI::used Cavity
`l..’o.ll Cavities for Producing Spectral Narrorvling ol’
`Lmer Dutpul
`Cavity with Additional Fabry—PE:tot Etaloo for Nat:Tow—Ftequency
`Selection
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`Tunable Cavity
`Bmadbcand Tunable cw Ring l..asers
`Tunable Cavity for U|tlanat'rmv-l-'-'requeocy Output
`Dl.5l.I'Il:|l.I[E:Cl Feedback {DFB} laser:
`Ilisuibutead Bragg Rzfleaction Lasers
`I19 Lmer Cavilie-5 Requiring Sliall-Diameter Cain llefions: —
`Aslignalic-ally Comlneoxatcd
`I3. 11] Waveguide Cavilie-s fior Gas 1351313
`REFERENCES
`HIDILIIMS
`
`SECFICIII 5. SPECIFIC LASER S"'I"':TI'EHS
`
`14 LASER SYSTEMS ||'Hl"H"OL"o"Il'lG I.'D'h'o'-DEIIISITY GAIN MEDIA
`DVEIITIEW
`14.1 Atomic Gas LISEIS
`lntroduclioo
`I-lel'nlI—Neon Lastr
`
`General Description
`laser Souclnrc
`Excitation Mechanism
`
`Applications
`Argon Ion Laser
`General Description
`Laser Souclnrc
`Excitation Mechanism
`
`Krypton [on Laser
`Applications
`I-lel'nlI—CaIimitIn1 laser
`
`General Description
`laser Souclnrc
`Excitation Mechanism
`
`Applications
`Copper Vapor Lat.-r
`General Description
`Laser Souclnrc
`Excitation Mechanism
`
`Applications
`
`468
`469
`4?!)
`
`4?ll
`
`4?!)
`4'.i"3
`
`4?B
`
`4TB
`
`4TB
`43!]
`43!]
`48]
`434
`
`434
`435
`-436
`433
`
`49]
`-49]
`49]
`49]
`492
`
`492
`493
`494
`
`497
`49'?
`49?
`493
`499
`
`SCI]
`50]
`50]
`
`50]
`502
`504
`
`505
`505
`505
`SOT
`50'?
`
`509
`
`
`
`
`
`
`
`

`
`CDIITENTS
`
`I-1.2 Molecular -Cas Lasers
`Introduction
`Carbon Dioxide Iiascr
`
`General Description
`Laser Structitrc
`Excitation Mochattisrn
`
`Applications
`E‘.I:t'.'l.I'IEI' Lasers
`
`Gcnsral Description
`laser Slt't.lt3l]tI'E'.
`Excitation I|tI'It=.:chat1isrn
`
`Applications
`Nitrogen Laser
`Gcntaral Description
`laser Structitrc and Excitation Mechanism
`
`Applications
`Far-Irtfrand Gas Lasers
`
`Gemaral Description
`Laser Structitrc
`Excitation Mechanism
`
`Applications
`CIIt:mit'al I.-Hers
`
`General Description
`Laser Structitrc
`Excitation I|tI'It=.:chat1isrn
`
`Applications
`InLl K-Ray Plasnu Lasers
`Introduction
`
`Purlzping Energy Requirements
`Excitation Itllrnchattism
`
`Optical Cam-itics
`J{—Ra3 Laser Transitions
`Applications
`I-LII Free-Electron liners
`Introduction
`Laser Structitrc
`
`Applications
`EEFEIENCES
`
`15 LASER SYSTEMS INVOLVING HIGH-DENSITY GAIIII MEDIA
`(WEIl1"lElI'
`
`15.] Organic Dye Lasers
`Introduction
`Laser Structitrc
`Excitation Mochattisrn
`
`Applications
`I52 Solid-State Lasers
`Introduction
`
`SH]
`SH]
`5] I
`5] I
`5] I
`515
`515
`Slti
`516
`51'?
`518
`52]]
`fill]
`510
`fill
`512
`512
`512
`513
`513
`514
`514
`52.4
`514
`514
`515
`515
`515
`515
`518
`532
`532
`532
`535
`535
`536
`53?
`53'?
`
`539
`539
`539
`539
`
`543
`
`545
`545
`
`
`
`
`
`
`
`

`
`54?
`54?
`
`SSIJ
`55!]
`55 1
`553
`554
`555
`555
`556
`556
`55?
`55?
`557
`55'?
`553
`553
`559
`559
`
`EDIIIEITS
`
`Ilubgr Laser
`General Description
`Laser Structure
`Excitation Mechanism
`
`.fltl;[JIit:atiI:|ns
`Neodynium TAG and Glam liners
`General Description
`Laser Structure
`Excitation |u'Ia::ltanisn1
`
`fitpplications
`Ncod3'nium:YI.F Lasers
`General Description
`Laser Structure
`Excitation lI'IecltaIIisn1
`
`fitpplications
`Neod3'nI'um:Yll.r'nm1 Vanadate I Nd:YVl)4} Lasers
`General Description
`Laser StI:1tctuI:e
`Excitation Mechanism
`
`Applicatiorm
`"k'llcrb1'mI:‘I'AG I..asers
`
`General Description
`Laser Stmctute
`Excitation Mechanism
`
`Applicatiorm
`Altxandrile Luer
`
`General Description
`Laser Stmctute
`Excitation Mechanism
`
`Applications
`Tilaniml Sqtplire Laser
`General Description
`Laser Structure
`Excitation |u'Ia::ltanisn1
`
`.fltl;[JIit:atiI:|ns
`Chronili LiSA.F anal IJCAF Ixaers
`
`General Description
`Laser Structure
`Excitation lI'IecltaIIisn1
`
`fitpplications
`P'Ibe1'Lasers
`
`General Description
`Laser Structure
`Excitation ltflencltanisnt
`
`Applicatiorm
`Color Dente1'I.'ae1's
`
`General Description
`Laser StI:1tctuI:e
`
`
`
`
`
`
`
`

`
`CDIITENTS
`
`Excitation Mechanism
`
`Applications
`15.! Sentionntinctor Diode Lasers
`Introduction
`
`Four Basic Types of Laser hI'lateria|s
`Laser Stmculre
`
`Freqtiency Control oflaaer Dutput
`Quantntn Cascade Lasers
`p—Dopetl Getinailium Lasers
`Excitation Mechanisrn
`
`Applications
`REFERENCES
`
`SECTION 6. FREGLIEHCY MUL'I'IPI.IEATIGH OF LASER BEAHS
`1G FREQUENCY MULTIPLICATIDH OF LASERS AND IEI"'|'HER
`HCIILIHEAR OPTICAL EFFECTS
`(WIIll'u"]IflI'
`
`lI‘3.l Wave Pmpnfilion in an Aniaolropii: E.'1'_vsia1
`I62 Pohriealion Response of h'[aleriaIa In Liglil
`IL! Second-Order NoI1I'lIenr'DpIit".|l P'rIooe-mes
`Second Harmonic Generation
`
`Burn and Difference Frequency Generation
`Dplical Pa:an1et|'ie Oscillation
`lfiol Third-Order Ntmlinear Optical Prncemes
`Thini Harmonic Generation
`
`[IEIlBl'ISil]|'—DBpBI'Id.BllI Refractive Index — Self-Focusing
`IE5 Nonlinear Iflplixral Maleriah
`lti.6 Phase Matching
`Description of Phase Malching
`Achieving Phase Matching
`Types of Phase Matching
`lI‘3.T Saturable .-Hlsorplinll
`IE3 Two-Photon Absorption
`lI‘3.'.I Slimtlaled Raman Scallt.-ring
`lI‘3.l'l]' Hannonic Gt-ner.I1inn in Cases
`REFERENCES
`
`Appendix
`Index
`
`5T4
`5'J"l.‘n
`5'J"l.‘n
`STE:
`5T9
`SEI
`5'E|'|
`592
`5'94
`5'94
`5'96
`5'97
`
`62 I
`615
`
`
`
`
`
`
`
`

`
`1 I
`
`ntroduction
`
`OUEEWEW A laser is a device Ihat amplifies light
`and pmdmres a highly diI1ectinnal_ high-intensity
`beam Ihatrnostoftenhosavetypure frequency or
` . ltcomesinsiees ranging from approx-
`intatelyoltetenlhtliediamelerofaltnrnanhairto
`Ihesieeofavetylasgebuilding;.inpourersrangir|g
`from I04‘ to lflm‘ ‘W, and in tuavelengtlis ranging
`irorntl1emicro'uravetotl|esoft—X-rayspectradmgiclrs
`wiflteolrespondingfroqpt-.|1cica from EU" to Ill" Hz.
`Lasers havepulseenezgieaas highas ll]‘l and pulse
`duiationsassholtmfi X IIl"5 s Theycaneasily
`iiill holes in the most durable of malerialsand-can
`
`oiexinenee!
`
`welddeiaclnedretiriasulililinthelnlrnaneye. They an:
`alcey eompnnent nfsmne nfour most mttlem com-
`munication systemsand a1e1he"“pbenograplI needle"
`oioureolnpoctdisc playels. They perform heat1Ie:rI-
`rnenstofhigh-atrength materials. mehas the pistons oi
`ourantornobile engines. and provide a special surgi-
`cal knife for manyI'.ypesoin1eIfical pn:I::edures_ They
`act as targetdesignstors for rnilitasytveapons andpro-
`vide for Ilse rapid cheek-out we ltave come to expect
`at the supermarket. Wltal a rernaEal:rlelangeofclral-
`aelcristics foradevice Ihatis in only its liflh decade
`
`INTRDDLICTIJN
`
`There is nothing magical about a laser. It can be thought ofasjust another type
`oi light source. Itcertainly has many unique properties that make it a special light
`source. but tllcae propeniescan be understood without toowledgeof sophticaieti
`rnathematical techniques oreomplca ideas. It isthe objective oithis teat toesplain
`theoperationoithelaserina simple, logical approach thatbuilds from one cotn-
`eepl In the ne:Ittasthe chapters evolve. The concepts, M they are developed, will
`be applied to all classes of laser rnflerials, so that the reader will develop a sense
`of the broad field of lasers while still acquiring the capability to study, design. or
`simply understand a specific type oflaser system in detail.
`
`DEFINITION OF THE LASER
`
`'I'he word laser is an acronym for Light Amplificilion by Stimulated Emiasi-on oi
`Radiation. The laser makes use of prooesses that increase or amplify light signals
`aflcrthose gnals have been genented by other means. These pI1o-ceases include
`(I) stimulated emission, a natunfl effect that was deduced by eonsiderations re-
`lating to tltennodynamic equilibrium, and {2} optical feedback {present in most
`
`
`
`
`
`
`
`

`
`
`
`in 1-1 Fmpilied
`sdtelnaiceftypicallamr
`
`Fully re1|e-sting
`rriror
`
`Optical resonator or cavity
`A
`
`Arnplltyiig msdlurn
`
`Parllall-.-1rmsnI1ting
`rriror
`
`liners) that is usually provided by nlirrnrs. Thus, in its simplest form, a [mercan-
`sists of a gain or amplifying medium {where stirnulated emimion oceans], and a
`set of minors to feed the Iiglitbaclr intolhe amplifier for continued growth ofthe
`developing bean, as seen in Egtre I-L
`
`5IhI'l.IZl1"f OF A LASER
`
`'l'|Ie simplicity ofa lasercm he understood by considering the light from acandle.
`Normally, a huming candle radiates light in all directions, flltll therefore illuJni-
`nales various objects equally if they are equidhtult from the candle. A lasertfies
`light that would nonrudly be emitted in all directions, such as from a candle, aid
`eoncenlraes that light into a single direction. Thus, iflhe light radialing in all di-
`rectiocmfrninacandle were trated into a singleli-eun nfthediilnelerofthe
`pupil ofyoureye tqnproxirruiely 3 mm}, and ifynu were slanding adistxmce of
`I m from the candle, then the light intensity would be l,EI]J,tIl1 times in laight as
`the light that you nnnndly see radiating from the candle! That is nlialljr the
`underlyingconcept ofthe operilinn ofalaser. Hcrwever, acandle is not the kind of
`medium that prodrces amplification, and thus there are no cantle lmets. It ties
`relatively special conditions within the laser medium foramplilicalinn to occur,
`but it istllat cqJal:Iilit3r oflaldng ligltt that would nor1IIall}r nalifle from asource in
`all directions — mid enncenlrfling that ligllt into alzneun traveling in a single direc-
`tion—ll:|al is involved in Initingalmer. These speciid conditiotui, and the media
`within which they are prmluced, will he descrilled in some detail in ll:Iis book.
`
`l.lNIt'.1l.E PROPEIITES CI: A LASER
`
`Tl1ebearnoflighlger|eriIedlJyat_-,rpi(:al lmercam havemanyprqyerliesfliatae
`unitple. ‘When eompaiing liner propelti to those ofnlber light sources. it can
`be readily recognized that the values of various paameters for laser light the:
`greaflyexcei.-4:lorareInucl:| mnnareslricti1rell1anthevalt|esfornul1ycomIruJn
`Iighlsources. We never use laseis for street illumination. orforillumination within
`our houses. We don't use them for seachliglits or flashlights or in headlights in
`
`
`
`
`
`
`
`

`
`IH1'IIDI'.|l.ICT|Dll
`
`our cue. Lasers generally have :1 narrower fI'B(].IEl:I:]|' distribution, or much higher
`in1Jensit}r, or :1 muclzl gleaierdegree ofeollimalion, or much shorter puhe tirtuion,
`lhanthu mraildrle from mole common lypesofliglrt sources. Tlrelefore, wedo use
`lhem in eonrpnct dhc players, in supeI1rul:‘keteheI:k—ou1 scazmers, in eunrejring in-
`stnrroenls, and in medical qzlplieafiorne 3 :1 arrgical knife or for welding detached
`retinas. We aha use fllem in comniuoicetiolzm systems and in lath" and roilitajr
`targeting q‘.-plicatiorrs, as well 3 men}! orther . A laser in: specialized Ifgfir
`.i‘DHfl.'£’ that should be used‘ a.n.f_I|.I when its unique pmpenie: are reqrrired.
`
`THE LASER SPECTRUM AII3 WAVELENGTPIS
`
`A portion oflhe e|e:et.I'on|ngr|elie nizlialion qrectnrm is drown in Figure I-2 for lhe
`region covered by currenfly existing lasers. Sucll lasers span lbe wan:-eIeng;fl1 nmge
`from the fariofriled part oflhe sp-e-I:tI1rm{J. = l,(I]1 urn} lo lhe eoft—X—|.'a}I region
`(11. : 3 om), dleaebyouveringarargeotfwnvelellgfllsotfahooelsixoldeas ofmag—
`nilude. There are several types of units fllat ale used lo define laser wavelenglirs.
`These range from mierometersorniicmns {taro} in the infrared to na1orneters{nm)
`aid angstroms {rat} in the visible, ultreu-'iole:l{UV ), vacuum ullnt-violet IIVUV], ex-
`treme ullnnriolet {EUV DIJCUV], and sofI—X-my (SICK) spectral regions.
`
`|'lI'.H'ELEIIG"I'H I.|llI'l'5
`
`I_rr.m = 1045 m:
`lA:l0'”m;
`Inm= Il}'9 rn.
`
`Coosetprelzrflgr, I mieroo{;.tm'j : l{},EIIlangstro|r|s{.r-it} : ],[I'.H'Jnenoroe‘IeI's {mo}.
`Forexanrple, green Iightbm eweveleoglhoffi x 10‘? m =l}.5 pun = 5,(I]1.:iL =
`SCI} run.
`
`KT
`
`I
`i
`-
`-. .
`..
`_ FIR La.-Lars
`
`'
`HF
`
`I
`'_'_'__
`
`9”“
`*9 '3'
`
`..
`in..
`
`..
`
`CO
`
`'
`
`"
`
`'
`
`Irgll-1-3‘N'a'IrE|Eng‘Ii'I
`range ul"va'inI.I5 hsers
`
`N:
`Hub)‘
`KrF
`He-Ne
`Nd:‘|'»|'-MEI
`He |'.‘-I
`
`s«:nt-x-Hen.-
`-.
`—
`Lasers
`
`co,
`
`Ha Ha
`
`Far Infrared
`
`Ifilrurtd
`
`_lZh;snm mu
`Ti:.B.IE03
`‘fisthlu
`
`nu:
`Ulren-Iolel
`
`SD?‘ Ill Ray:
`
`eupm mum
`
`3pm T,»-n
`-up
`
`I
`
`3|]-Dnm ‘lcH]nm snnm 1EInrn
`
`-——--- ENERGY
`
`-..
`
`
`
`
`
`
`
`

`
`INTRODUCTION
`
`VHIHELEIIGTH IIEGIDHS
`
`Far inflated: II] to LEIII _u'.m;
`middle infrared: I to 10 em;
`nearinfrared: 0.? to I pm;
`visible: 0.4- to I].T pun, or 4III] to 'i'{Il run;
`ultraviolet: 0.2 to {Lt-‘I fltll, or 21]} to 4-{ll run;
`vacuum ultraviolet: 11.] to 0.2 pm, or III] to ZEN] I'LI'l:I',
`extreme ultraviolet: IO to [CI] nm;
`soil X—ra}rs:
`1 nm to approximately 20-30 n|:n {some overlap with EUV].
`
`A BREF HISTORY OF THE LASER
`
`Charles Townes took advantage of the stimulated entission procem to construct a
`microwave amplifier, referredtoasallmrer. 'l'bisdevi:ce pruiucedacnherent bearn
`oi microwaves to be used for conununications. The firsl rnaser was produced in
`ammonia vapor with the inversion between two energy levelslhat produced gain at
`a wavelength of [.25 cm. The wavelengtlzs produced in the maserweie compara-
`ble to the dimensions of die device, so exuapilation to die optical regime — wbeae
`wavelengths were live orders ofrnagnitude si:na]ler— was not an ohviousestermion
`oi that work.
`
`In 1955, Townes and S-chawlow published a paperconcerning theiridem about
`extending tlte rnmer concept to optical frequencies. They developed the concept
`oian optical amplifier surrounded by an optical rnirror resonantcavity to allow for
`growth ofthe hearn. Townes and S-chawlow 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 ampliflerandaflashlampas the energy source.
`The helical flashlamp sulroutded a rod—shaped rub}! crystal, and the optical cavity
`was formed by mating the flattenul ends ofthe I'I.IlJl)|' ro.'.I. with a highly reflecting
`material. Anintenseledbeamwasobservedtoernergefrorntheendoftherod
`when the Ilashla.mp was fired!
`The firstgaslmerwasdevelopedin I96] b}'A.lavan,‘W. Bennett, and D. Har-
`riott of Bell Laboratories, using a mixture oi helium and neon gases. At the same
`laboratories, L. F.Johnson and K. Nassau demonstrated the first neodvmiurn laser,
`whichhassiricebeeomeoneofthernostreliahlelasersavailahle. This was followed
`
`in [962 by the first semiconductor laser, demonsuated by R. Hall at the General
`Elect.ric Research Laboratories. In 1963, C. K. N. Patel of Bel] laboratories dis-
`covered the infrared carhon dioxide laser, which is one of the most e:FIicient and
`powerful lasers available today. Later that sa.Ine year, E. Bell of Spectra Phvsies
`discovered the lirst ion laser, in rnercuqr vapnr. In l96r-‘I W. Bridges ofHugbes Re-
`search Lahoratori discovered the argon ion laser, and in I966 W. Silfvafl, G. R.
`Fowles, and B. D. Hopkire produced the fun blue helium—cadI:nium metal vapor
`
`
`
`
`
`
`
`

`
`INTIDDIICTIDN
`
`laser. During thatsame yea", P. P. S-orolzinand J.R..L£I1lLard otthe IBM Research
`Leboratoriesdevelopedllre firn liquid laser using an organicdyedissolved in aeol-
`rrent, thereby leading to the category oi broadly tumble lasers. Also-£1 that time,
`W.‘WaIlerandco—workers atTRGreporled the lilstcopperyaporlaser.
`The first vacuum ultraviolet laser was repnrted to occur in molecular hydro-
`genb-yR.Hodgsono1'IBMand'rndependentlyhyI?l‘..‘Way|rar1telal.ot'theI*la-rral
`Research Laboratories in I970. The fun oi the well-known rare-gas—halide ex-
`ccimer lasers wm observed in xenon fluoride by J. J. Ewing and C. Brau ol'the
`J't1rco—EveIe'lt Research Laboratory in I975. In that. same year, the fiist quar1t.rIm-
`well laser was made in a gallium arsenide semiconductor by J. van der Zie] and
`co—worlcers at Bell Iaboratories. In I976, I. M. I. Marley and co-workers 3. Stan-
`ford University demonstrated the lirsr l'ree—eIect.ron laserarnplifier operating in the
`infrared at. the DD; laser wavelength. In l'JiI'9, Walling and co—worleers 5!. Allied
`CIIemicalCor|:I1ration obtainai broadly tunable Iaseroutpulfromasolid.-statelaser
`material called aleirandlile, and in I985 the first sot't—X—ray laser was successfully
`demonstrated inabigbly ion'r;red.seliurn
`D. MatthewsarrdaI2I'genrIm-
`ber ol co—worlr.ers at. the Lawrence Livermore . In l9B6, P. lvloulton
`discovered the titanium sapphire laser. In ]99l, M. Hme and co-workers devel-
`oped the that blue—green diode laser in Znfle. In I99-'-I, F. Chpwo and cn—worI:ers
`developed the qrrantrlm cascade laser. In I996, S. Nalrarnura developed the lirsl
`blue diode laser in GaN—bmed materials.
`
`In 196], Fox and Li described the existence olonant transverse modes in
`a laser cavity. That. same yea", Boyd and (hrdon obtained solutions of the wave
`equation for confocal resonator modes. Unstable resonators were demonstrated
`in 1969 by Krupke and Sony ind were described theoretically by Siegrnan. Q-
`switching was first obtained by h'[cC.']ung and I-Iellwarth in 19452 and described
`later by ‘Wagner and Lengyel. The first mode-locking was obtained by I-Iargrn-Ire,
`Fork, and Pollack in I964. Since then, many special cavity anangements, Ieedback
`scherrres, and otherdevices have been developed to improve thecontrol, operuion,
`and reliability oflasers.
`
`OVERVIEW OF THE BDCIK
`
`Isaac Newton described Iigln as small bodies emitted from drining suhstserces.
`This ‘||'I.B"I\|' was no doubt influenced by the fact that. light appears to propagate in a
`line. Chriflian 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 difliaclion, reflection, and relraclion —cil1 be atlribuletl to-the expansion
`ol'prirniI'y wa-«rm and of secondary wavelets. The dual natrl'e of light is still ause—
`ful concept, whereby the choice of panicle or wave explanation depends upon the
`effect to be considered.
`
`film Dneoithis bcnkdealswilh thefrlndarrrental w:rrve'prr:Jperties-r:d'Iigh1,
`including lh'Ia:rwel]'s equations, the interaction oi electromagnetic r