Tunable lasers handbook phần 1 ppt

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 Zora

H A N D B O O K

'TICS AND PHOTONICS

t

I

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

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

1 Tunable lasers I Title 11 Series

cm - (Optics and photonics series)

TA1706.D83 1995

CIP PRINTED IN THE UNITED STATES OF AMERICA

95 96 9 7 9 8 99 0 0 E B 9 8 7 6 5 4 3 2 1

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

9 Transmission Efficiency of Multiple-Prism Compression 23

Arrays 24 Appendix: Dispersion of Multiple-Prism Arrays and 4 x 4 Transfer Matrices

2 Excimer Active Media 35

3 Tuning of Discharge and Electron Beam Pumped

4 Discharge Excimer Lasers 53 Excimer Lasers 41

Con tents 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

1 1 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

14 Spectroscopic Use of CO, Lasers outside Their

Stabilized CO, Laser Transitions 154

Fundamental 8.9- to 12.4-pm Wavelength Range References 16 1

159

1 Introduction 167

2 Laser-Pumped Pulsed Dye Lasers

3 Flashlamp-Pumped Dye Lasers 179

4 cw Laser-Pumped Dye Lasers

5 Femtosecond-Pulsed Dye Lasers 191

6 Solid-state Dye Lasers 195

2 Transition Metal and Lanthanide Series Lasers 225

3 Physics of Transition Metal Lasers

4 Cr:A1,0, 246

5 Cr:BeA1,04 251

6 Ti:Al,O, 258

7 Cr:LiCaA1F6 and Cr:LiSrAlF, 263

8 Cr:GSGG, Cr:YSAG, and Cr:GSAG 270

9 Co:MgF,, Ni:MgF,, and VMgF,

18 Wavelength Control Methods 281

232

275 References 288

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

Feedback Model 375 External-Cavity Design 377 Cavity Components 383 Survey of External-Cavity Laser Designs Mode Selectivity of Grating Cavities 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

398

407

Contents iX

Stephen Vincent Benson

1 Introduction 443

2 Methods of Wavelength Tuning

3 Broadly Tunable Optical Cavities

Contributors

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

Charles Freed (63), Lincoln Laboratory and the Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Lexington, Massachusetts 02173

ginia 23681

Beam Accelerator Facility, Newport News, Virginia 23606

D G Harris (33), Rockwell International, Canoga Park, California 91309

87545

Laboratories, Palo Alto, California 94303

xi

Preface

Light and color are concepts that have always invoked thoughts of joy and won- der 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 sati- ated” (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 appli- cations 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, tun- able CO, lasers, dye lasers, tunable solid-state lasers, optical parametric oscilla- tors, 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 appli- cations in science, technology, and industry For instance, the first broadly tun- able 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 tun- able 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 emis- sion characteristics Notable among these sources are optical parametric oscilla- tors 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

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

TABLE 1 Wavelength Coverage Available from Pulsed Broadly Tunable Sources

of Coherent Radiation

Source Wavelength range

OPO

Free-electron lasers (FELs) 2 urn-1 mmb [I71

UWavelength range covered with the use of various dyes

Kombined wavelength range from several free-electron lasers

TABLE 2 Wavelength Coverage Available from cw Broadly Tunable Lasers

Laser source Wavelength range

0 Wavelength range covered with the use of various dyes

bWavelength range of single-longitudinal-mode emission Tuning range limited by coatings of Wavelength tuning achieved using external cavity designs

mirrors [19] Commercial designs offer extended tuning ranges beyond 1000 nm

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 radia- tion 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 Ener- getic 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 gener- ation 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

Coherent Radiation

Energy and Power Characteristics from Broadly Tunable Sources of

Source Pulse regime cw regime

Energy0 Power Powera

Dye lasers 400 J h [26] 2.5 kW at 13.2 ! d I z c [27] 43 Wd [28]

Ti?+:AI,O, laser 6.5 Jb,e [29] 5.5 W at 6.5 kHz( [30] 43 Wdf[32]

Cr3+:BeAI2O4 laser >lo0 Jh [33] 6.5 Ws [34]

- GW levels in short pulses [I71

UThese values may represent the best published performance in this category

hUnder flashlamp excitation

dUnder AI? laser excitation

eUses laser dye transfer in the excitation

fliquid-nitrogen cooled

wUnder Hg-lamp excitation

Under copper-vapor-laser (CVL) 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 intrinsi- cally in the short-pulse regime with pulses as short as 250 fs [17]

2 TUNABLE LASER COMPLEMENTARITY

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 deter- mine 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 selec- tion 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 follow- ing 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 in

reference to isotope separation In this regard, the necessary spectroscopic infor- mation 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 tun- able 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 OF THIS BOOK

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 chap- ters go beyond the classical concept of a handbook and provide a detailed dis- cussion 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 dis- cretely tunable lasers and broadly tunable lasers Discretely tunable lasers are considered first because that also satisfies the more technocratic division of the

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 Chap- ter 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 tun- able 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 exam- ple, 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 fre- quency shifting via nonlinear optics techniques such as Raman shifting

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