Tunable lasers handbook f duarte

H A N D B O O K

t

I
'TICS AND PHOTONICS




Tunable

Lasers

H A N D B O O K


OPTICS AND PHOTONICS
(formerly Quantum Electronics)
SERIES EDITORS

PAUL E LIAO
Bell Communications Research, Inc.
Red Bank, New Jersey

PAUL L. KELLEY
Lincoln Laboratory
Massachusetts Institute of Technology
Lexington, Massachusetts

IVAN P. KAMINOW

AT&T Bell Laboratories

Holmdel, New Jersey

A complete list of titles in this series appears at the end of this volume


Tunable

Lasers
A N D B O
Edited by

F. J. Duarte
Eastman Kodak Company
Rochesrer, New York

ACADEMIC PRESS
San Diego New York Boston
London

Sydney Tokyo Toronto


This book is printed on acid-free paper.

@

Copyright 0 1995 by ACADEMIC PRESS, INC.
All Rights Reserved.

No part of this publication may be reproduced or transmitted in any form or by any
means, electronic or mechanical, including photocopy, recording, or any information
storage and retrieval system, without permission in writing from the publisher.

Academic Press, Inc.
A Division of Harcourt Brace & Company
525 B Street, Suite 1900, San Diego, California 92101-4495
United Kingdom Edition published by
Academic Press Limited
24-28 Oval Road, London NW1 7DX
Library of Congress Cataloging-in-Publication Data
Duarte, F. J. (Frank J.)
Tunable lasers handbook / F. J. Duarte.
cm. - (Optics and photonics series)
p.
Includes index.
ISBN 0-12-222695-X
1. Tunable lasers. I. Title. 11. Series.
TA1706.D83 1995
621.36'6-dc20
PRINTED IN THE UNITED STATES OF AMERICA
95 96 9 7 9 8 99 0 0 E B 9 8 7 6 5

95-8165
CIP
4

3 2 1

Contents

Contributors xi
Preface xiii

1. Introduction 1
2. Tunable Laser Complementarity 4
3. GoalofThisBook 5
References 6

and Intracavity Dispersion
F. J. Duarte
1. Introduction 9
2. Dispersive Oscillator Configurations

10


vi

Contents

3. Physical Dimensions 15
4. Generalized Interference Equation 16
5. Dispersion Linewidth Equation 17
6. Beam Divergence 19
7. Intracavity Dispersion 19
8. Intracavity Multiple-Prism Dispersion and Pulse
Compression 23
9. Transmission Efficiency of Multiple-Prism

Arrays 24
10. Wavelength Tuning 26
Appendix: Dispersion of Multiple-Prism Arrays
and 4 x 4 Transfer Matrices 29
References 3 1

D. G. Harris
1. Introduction 33
2. Excimer Active Media 35
3. Tuning of Discharge and Electron Beam Pumped
Excimer Lasers 41
4. Discharge Excimer Lasers 53
References 59

Charles Freed

1. Introduction

63

2. Vibrational Energy-Level Structive of the CO,

Molecule 65
3. Rotational Energy-Level Substructure of the CO,
Molecule 69
4. Processes Governing the Excitation of Regular Band
Laser Transitions in CO, 7 1
5. Additional Characteristics of Regular Band CO,
Lasers Transitions 74
6. Lineshape Functions and Broadening Due to Gas

Pressure and Doppler Shift in CO, Gas 76
7. Spectral Purity and Short-Term Stability 79


Contents

vi

8. Long-Term Line-Center Stabilization of CO,
Lasers 82
9. Absolute Frequencies of Regular Band Lasing
Transitions in Nine CO, Isotopic Species 95
10. Pressure Shifts in Line-Center-Stabilized CO,
Lasers 137
11. Small-Signal Gain and Saturation Intensity of
Regular Band Lasing Transitions in Sealed-off
CO, Isotope Lasers 144
12. Laser Design 149
13. Spanning the Frequency Range between Line-Center
Stabilized CO, Laser Transitions 154
14. Spectroscopic Use of CO, Lasers outside Their
Fundamental 8.9- to 12.4-pm Wavelength Range 159
References 161

1.
2.
3.
4.

Introduction 167

Laser-Pumped Pulsed Dye Lasers 172
Flashlamp-Pumped Dye Lasers 179
cw Laser-Pumped Dye Lasers 184
5. Femtosecond-Pulsed Dye Lasers 191
6. Solid-state Dye Lasers 195
Appendix of Laser Dyes 200
References 215

Transition Metal Solid-state Lasers
Norman P. Barnes

1.
2.
3.
4.
5.
6.
7.
8.
9.
18.

Introduction 219
Transition Metal and Lanthanide Series Lasers 225
Physics of Transition Metal Lasers 232
Cr:A1,0, 246
Cr:BeA1,04 251
Ti:Al,O, 258
Cr:LiCaA1F6and Cr:LiSrAlF, 263
Cr:GSGG, Cr:YSAG, and Cr:GSAG 270

Co:MgF,, Ni:MgF,, and VMgF, 275
Wavelength Control Methods 281
References 288


viii

Contents

Norman P. Barnes
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

Introduction 293
Parametric Interactions 297
Parametric Oscillation 301
Spectral Bandwidth and Acceptance Angles
Birefringence Effects 3 14
Average Power Limitations 3 17
Nonlinear Crystals 321
Phase-Matching Calculations 328
Performance 334

Tuning 343
References 345

306

Tunable External-Cavity
Semiconductor Lasers
Paul Zorabedian
1.
2.
3.
4.

5.
6.
7.
8.
9.
10.
11.
12.

13.
14.
15.
16.
17.
18.

Introduction 349

Semiconductor Optical Gain Media 352
Classes of External-Cavity Lasers 368
First-Order Properties 370
Feedback Model 375
External-Cavity Design 377
Cavity Components 383
Survey of External-Cavity Laser Designs 398
Mode Selectivity of Grating Cavities 407
Phase-Continuous Tuning 409
Characterization Methods for External-Cavity
Lasers 412
Measurement of Facet and External-Cavity
Reflectances 4 12
Multimode Suppression 417
Multiple-Wavelength Operation 420
Wavelength Stabilization 42 1
Advanced Modeling Topics 422
Construction and Packaging 427
Applications 430
References 435


Contents

Stephen Vincent Benson

1.
2.
3.
4.

5.

Introduction 443
Methods of Wavelength Tuning 450
Broadly Tunable Optical Cavities 456
Wiggler Considerations 459
Tunable Laser Facilities and Their
Characteristics 460
6. Summary 468
References 468

Index 471

iX



Contributors

Numbers in parentheses indicate the pages on which the authors' contributions begin

Norman P. Barnes (219,293), NASA Langley Research Center, Hampton, Virginia 23681
Stephen Vincent Benson (443), Accelerator Division, Continuous Electron
Beam Accelerator Facility, Newport News, Virginia 23606
E J. Duarte (1,9, 167), Eastman Kodak Company, Rochester, New York 14650
Charles Freed (63), Lincoln Laboratory and the Department of Electrical
Engineering and Computer Science, Massachusetts Institute of Technology,
Lexington, Massachusetts 02173
D. G. Harris (33), Rockwell International, Canoga Park, California 91309
R. C. Sze (33), Los Alamos National Laboratory, Los Alamos, New Mexico

87545
Paul Zoralbedian (349), Photonic Technology Department, Hewlett-Packard
Laboratories, Palo Alto, California 94303

xi



Preface

Light and color are concepts that have always invoked thoughts of joy and wonder. Perhaps the essence of light is well captured in the realm of poetry where
light has been identified as a “changing entity of which we can never be satiated” (Gabriela Mistral, 1889-1957).
This book is about changing light; it is about light sources that emit the
colors of the rainbow and beyond. Indeed, the central theme of this book is
changing light of high spectral purity or, as a physicist would say, tunable
coherent radiation.
Tunable lasers ar unique physical systems that enjoy an abundance of applications ranging from physics to medicine. Given this utilitarian aspect, the sense
of wonder in tunable lasers extends beyond beauty.
Tunable Lasers Handbook provides a broad and integrated coverage of the
field, including dispersive tunable laser oscillators, tunable excimer lasers, tunable CO, lasers, dye lasers, tunable solid-state lasers, optical parametric oscillators, tunable semiconductor lasers, and free electron lasers. In this regard, the set
of coherent sources considered here spans the electromagnetic spectrum from
the near ultraviolet to the far infrared. Further features are the inclusion of both
discretely and broadly tunable lasers, pulsed and continuous wave lasers, and
gain media in the gaseous, liquid, and solid state.

xiii


xiv

Preface

Although the basic mission of this work is to offer an expeditious survey of
the physics, technology, and performance of tunable lasers, some authors have
ventured beyond the format of a handbook and have provided comprehensive
reviews.
This project was initiated in 1990. Completion in late 1994 has allowed the
inclusion of several recent developments in the areas of solid-state dye lasers,
optical parametric oscillators. and external cavity tunable semiconductor lasers.
The editor is particularly grateful to all contributing authors for their hard work
and faith in the vision of this project.

E J. Duarte
Rochester; NY
January 1995


Eastman Kodak Company

Rochester, New York

1. INTRODUCTION
Tunable sources of coherent radiation are suitable for a wide range of applications in science, technology, and industry. For instance, the first broadly tunable laser source, the dye laser, is used for a plethora of applications in many
diverse fields [ 11 including physics [ 2 4 ] , spectroscopy [5,6],isotope separation
[6-81, photochemistry [9], material diagnostics [9], remote sensing [9-11], and
medicine [12]. In addition to issues of physics, it is this utilitarian aspect of tunable lasers that motivates much of the interest in the field.
In recent years, new sources of tunable coherent radiation have become
available that have either extended spectral coverage or yielded appealing emission characteristics. Notable among these sources are optical parametric oscillators and tunable semiconductor lasers.
This field has several natural subdivisions. For instance, although most
sources of tunable coherent radiation are lasers, some sources such as the optical

parametric oscillator (OPO) do not involve population inversion. An additional
classification can be established between broadly tunable sources of coherent
radiation, including broadly tunable lasers, and discretely tunable lasers, and/or
line-tunable lasers. A subsequent form of classification can be the physical state
of the difFerent gain media such as gaseous, liquid, and solid state. Further
Tunable Lasers Handbook
Copyright 0 1995 by Academic Press, Inc. All rights of reproduction I any form reserved
n


2

F. J. Duarte

avenues of differentiation can include the required method of excitation and the
mode of emission, that is, pulsed or continuous wave (cw). Moreover, sources of
tunable coherent radiation can be further differentiated by the spectral region of
emission and energetic and/or power characteristics. Also, in the case of pulsed
emission, pulse duration, and pulse repetition frequency (prf) are important.
The spectral coverage available from pulsed broadly tunable sources of
coherent radiation is listed in Table 1. The spectral coverage available from cw
broadly tunable lasers is given in Table 2 and emission wavelengths available

T B E 1 Wavelength Coverage Available from Pulsed Broadly Tunable Sources
AL
of Coherent Radiation
Source

Wavelength range

Dye lasers

320-1 200 nmo [ 131

Ti3+:A1,03 laser
Cr3+:BeAl2O, laser

660-986 nm [ 141
701-818 nm [I51

OPO
BBO
Free-electron lasers (FELs)

0.41-2.7 pm [I61
2 urn-1 mmb [I71

UWavelength range covered with the use of various dyes.
Kombined wavelength range from several free-electron lasers.

T B E 2 Wavelength Coverage Available from cw Broadly Tunable Lasers
AL
Laser source

Wavelength range

Dye lasers
Ti3+:AI2O, laser
Semiconductor lasersc
InGaAsPDnP

InGaAsPDnP
GaAlAs
GaAlAs

320-1000 rima [18]
710-870 nmh [19]

~

55 nm at 1500 nm [20]
1255-1335 nm [21]
815-825 nm [22]
20 nm at 780 nm [23]

0 Wavelength range covered with the use of various dyes.
bWavelength range of single-longitudinal-mode emission. Tuning range limited by coatings of
mirrors [19]. Commercial designs offer extended tuning ranges beyond 1000 nm.
c Wavelength tuning achieved using external cavity designs.


1 Introduction

3

from discretely tunable lasers are listed in Table 3 of Chapter 5. The information
provided in these tables indicates that broadly tunable sources of coherent radiation span the electromagnetic spectrum from -300 nm to -1 mm. Excimer lasers
offer limited tunability in regions further into the ultraviolet around 193 and 248
nrn. The tuning ranges quoted for ArF and KrF lasers are -17,000 GHz and
-10,500 GHz [24], respectively. An exception among excimer lasers is the XeF
laser with its C+A transition, which has demonstrated broadly tunable emission

in the 466- to 512-nm range [25]. In Table 3 of Chapter 5 bandwidth and tuning
range information is included for a variety of discretely tunable lasers including
excimer, N,, HgBr, and Cu lasers. Wavelength information on line-tunable cw
lasers such as Ar+ and the Kr+lasers is included in Table 11 of Chapter 5. Energetic and power characteristics of some tunable sources of coherent radiation are
listed in Table 3 of this chapter. Although the title of this book refers specifically
to tunable [users,sources that do not involve population inversion in their generation of coherent radiation are included. This approach is justified because the
issue under consideration is the generation of tunable coherent radiation, which
is precisely what OPOs perform.
In the area of ultrashort-pulse generation, dye lasers have demonstrated
17 fs using intracavity pulse compression [36] and 6 fs using further extra

TABLE 3 Energy and Power Characteristics from Broadly Tunable Sources of
Coherent Radiation
Source

Pulse regime

cw regime

Energy0

Ti?+:AI,O, laser
Cr3+:BeAI2O4
laser
OPOS
BBO

Powera

400 J h [26]

6.5 Jb,e [29]

Dye lasers

Power.
2.5 kW at 13.2 ! d I z c [27]
5.5 W at 6.5 kHz( [30]
220 W at 110 H z b [31]

43 Wd [28]
43 Wdf[32]

>lo0 Jh [33]
>lo0 mJ [16]

LrnO,
FELS

6.5 Ws [34]

10 mW [35]

- GW levels in short pulses [I71

UThese values may represent the best published performance in this category.
hUnder flashlamp excitation.
Under copper-vapor-laser (CVL) excitation.
dUnder A ?laser excitation.
I
eUses laser dye transfer in the excitation.

fliquid-nitrogen cooled.
wUnder Hg-lamp excitation.


4

F. J. Duarte

cavity compression [37]. Utilizing intracavity negative dispersion techniques,
Ti3+:Al,03 lasers have yielded 11 fs [381. Also, 62 fs have been reported in
OPOs using extracavity compression [39]. Emission from FELs is intrinsically in the short-pulse regime with pulses as short as 250 fs [17].

2. T N B E LASER C M L M N A I Y
UAL
O P E E T RT
From the data given previously it could be stated that tunable sources of
coherent radiation span the electromagnetic spectrum continuously from the near
ultraviolet to the far infrared. However, this claim of broad coverage is sustained
from a global and integrated perspective of the field. Further, a perspective of
complementarity is encouraged by nature, given that different sources of tunable
coherent radiation offer different optimized modes of operation and emission.
In this context, under ideal conditions, the application itself should determine the use of a particular laser [40,41]. This perspective should ensure the
continuation of the utilitarian function traditional of the early tunable lasers that
ensured their success and pervasiveness.
To determine an appropriate laser for a given application, the logic of selection should identify the simplest and most efficient means to yield the required
energy, or average power, in a specified spectral region. In practice, the issue
may be complicated by considerations of cost and availability. In this regard,
selection of a particular pulsed laser should include consideration of the following parameters:

1. Spectral region

2. Pulse energy
3. Average power (or prf)
4. Cost (capital and operational)
5. Environment.
More subtle issues that are also a function of design include the following:

6. Emission linewidth
7. Wavelength and linewidth stability
8. Pulse length (femtoseconds, nanoseconds, or microseconds)
9. Physical and optical ruggedness
10. Amplified spontaneous emission (ASE) level.
A basic illustration of complementarity is the use of different types of lasers
to provide tunable coherent radiation at different spectral regions. For instance.
FELs can be recommended for applications in need of far-infrared emission,
whereas dye lasers are suitable for applications requiring high average powers in
the visible.


1 Introduction

5

A more specific example of the complementarity approach can be given i
n
reference to isotope separation. In this regard, the necessary spectroscopic information including isotopic shifts, absorption linewidths, and hyperfine structure
can be studied using narrow-linewidth tunable cw lasers. On the other hand, for
successful large-scale laser isotope separation high-average-power pulsed tunable lasers are necessary [6,27]. A further example is the detection and treatment
of surface defects in optical surfaces being used in the transmission mode for
imaging applications. The detection and assessment of the surface defects is
accomplished using interferometry that applies tunable narrow-linewidth cw

lasers. Surface treatment requires the use of pulsed lasers operating in the high
prf regime.
Recently, complementarity in tunable lasers has been taken a step further
with the integration of systems that utilize complementary technologies to
achieve a given performance. An example is the use of a semiconductor-laser
oscillator and a dye-laser amplifier [42]. Also, the event of high-performance
solid-state dye-laser oscillators [43] has brought the opportunity to integrate
these oscillators into OPO systems [44].

3. GOAL O THIS BOOK
F
The goal of this book is to provide an expeditious guide to tunable sources
of coherent radiation and their performance. Issues of physics and technology
are also considered when judged appropriate. In this book, this judgment has
been made by each individual contributor. Although the basic function of a
handbook is to tabulate relevant physical and performance data, many works
under that classification go beyond this basic format. In this book, several chapters go beyond the classical concept of a handbook and provide a detailed discussion of the data presented.
From a practical perspective, the intended function of this book is to offer
scientists and engineers the means to gain an appreciation for the elements and
performance of tunable lasers and ultimately to assist the reader to determine the
merit of a particular laser relative to a given application.

3.1 Book Organization
The book is divided into nine chapters including this introduction. A chapter
on narrow-linewidth oscillators is introduced prior to the main collection of
chapters given the broad applicability of the subject matter. The main body of
the book is basically organized into two groups of chapters categorized as discretely tunable lasers and broadly tunable lasers. Discretely tunable lasers are
considered first because that also satisfies the more technocratic division of the

6

F. J. Duarte

subject matter in terms of physical state, that is, gas, liquid, and solid-state lasers
consecutively. Here, note that because dye lasers have been demonstrated to lase
in the three states of matter, their positioning between gas and solid state is quite
appropriate. Free-electron lasers are listed at the end of the broadly tunable
coherent sources given their uniqueness as physical systems.
Chapter 2 treats narrow-linewidth oscillators and intracavity dispersion.
The subject matter in this chapter is applicable to both discretely and broadly
tunable lasers in the gaseous, liquid, or solid state. Chapter 3 addresses tunable
excimer lasers including ArF, KrF, XeC1, and XeF. Chapter 4 is dedicated to
tunable CO, lasers oscillating in the cw regime. These two chapters deal with
discretely tunable lasers in the gaseous phase.
Broadly tunable sources and lasers are considered in Chapters 5 to 9. Chapter 5 deals with dye lasers and Chapter 6 with transition metal solid-state lasers.
The latter chapter includes material on Ti3+:A1,03 and Cr3+:BeAl,04 lasers.
Chapter 7 considers the principles of operation and a variety of crystals used in
optical parametric oscillators. The subject of tunable semiconductor lasers is
treated in Chapter 8 with emphasis on external cavity and wavelength tuning
techniques. Chapter 9 provides an up-to-date survey of free-electron lasers.
For historical information and basic references on the various types of tunable lasers, the reader should refer to the literature cited in the chapters. The
reader should also be aware that the degree of emphasis on a particular laser
class follows the judgment of each contributing author. In this regard, for example, high-pressure pulsed CO, lasers are only marginally considered and the
reader should refer to the cited literature for further details. A further topic that is
related to the subject of interest, but not a central objective of this volume, is frequency shifting via nonlinear optics techniques such as Raman shifting.

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1 Introduction
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