Solid-State Laser Engineering

618 Pages·1988·18.892 MB·English

by  Dr. Walter Koechner (auth.)

Springer Series in Optical Sciences Volume 1
Springer Series in Optical Sciences
Editorial Board: D .L. MacAdam A.L. Schawlow K. Shimada A. E. Siegman T. Tamir
Managing Editor: H. K. V. Latsch
42 Principles of Phase Conjugation 51 1\mable Solid State Lasers for Remote Sensing
By B. Ya. Zel'dovich, N.F. Pilipetsky, Editors: R. L. Byer, E. K. Gustafson,
and V. V. Shkunov and R. Trebino
43 X-Ray Microscopy
52 Tunable Solid-State Lasers II
Editors: G. Schmahl and D. Rudolph
Editors: A.B. Budgor, L. Esterowitz,
44 Introduction to Laser Physics and L. G. DeShazer
By K. Shimoda 2nd Edition
53 The C02 Laser By W.J. Witteman
45 Scanning Electron Microscopy
Physics of Image Formation and Microanalysis 54 Lasers, Spectroscopy and New Ideas
By L. Reimer A Tribute to Arthur L. Schawlow
Editors: W. M. Yen and M.D. Levenson
46 Holography and Deformation Analysis
By W. Schumann. J.-P. Ziircher, and D. Cuche
55 Laser Spectroscopy VIII
47 Tunable Solid State Lasers Editors: W. Persson and S. Svanberg
Editors: P. Hammerling, A.B. Budgor,
and A. Pinto 56 X-Ray Microscopy II
Editors: D. Sayre, M. Howells, J. Kirz, and
48 Integrated Optics H. Rarback
Editors: H. P. Nolting and R. Ulrich
57 Single-Mode Fibers Fundamentals
49 Laser Spectroscopy VII
By E.-G. Neumann
Editors: T. W. Hansch and Y. R. Sherr
50 Laser-Induced Dynamic Gratings 58 Photoacoustic and Photothermal Phenomena
By H.J. Eichler, P. Giinter, and D. W. Pohl Editors: P. Hess and J. Pelzl
Volumes 1-41 are listed on the back inside cover
Walter Koechner
Solid-State
Laser Engineering
Second Completely Revised and Updated Edition
With 371 Figures
Springer-Verlag Berlin Heidelberg GmbH
Dr. WALTER KOECHNER
Fibertek, Inc., 510-A Herndon Parkway,
Herndorn, VA 22070, USA
Editorial Board Professor Korcm SHIMODA, Ph. D.
Faculty of Science and Technology
Keio University, 3-14-1 Hiyoshi, Kohoku-ku
Yokohama 223, Japan
DAVID L. MACADAM, Ph. D. Professor ANTHONY E. SIEGMAN, Ph. D.
68 Hammond Street Electrical Engineering
Rochester, NY 14615, USA E. L. Ginzton Laboratory, Stanford University
Stanford, CA 94305, USA
ARTHUR L. ScHAwLow, Ph. D. THEODOR TAMIR, Ph. D.
Department of Physics, Stanford University Polytechnic University
Stanford, CA 94305, USA 333 Jay Street, Brooklyn, NY 11201, USA
Managing Editor: Dr. HELMUT K. V. LaTSCH
Springer-Verlag, Tiergartenstrasse 17, D-6900 Heidelberg, Fed. Rep. of Germany
ISBN 978-3-662-15145-7 ISBN 978-3-662-15143-3 (eBook)
DOI 10.1007/978-3-662-15143-3
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©Springer-Verlag Berlin Heidelberg 1976 and 1988
Originally published by Springer-Verlag Berlin Heidelberg New York in 1988
Softcover reprint of the hardcover 2nd edition 1988
The use of registered names. trademarks, etc. in this publication does not imply, even in the absence
of a specific statement, that such names are exempt from the relevant protective laws and regulations
and therefore free for general use.
2154/3150-543210-Printed on acid-free paper
Preface to the Second Edition
This monograph, written from an industrial vantage point, provides a detailed
discussion of solid-state lasers, their characteristics, design and construction,
and practical problems. The title Solid-State Laser Engineering is chosen so as
to convey the emphasis which is placed on engineering and practical consider
ations.
The author has tried to enhance the description of the engineering aspects
of laser construction and operation by including numerical and technical data,
tables, and curves.
The book is mainly intended for the practicing scientist or engineer who
is interested in the design or use of solid-state lasers, but it is hoped that
the comprehensive treatment of the subject makes the work useful also to
students of laser physics who want to supplement their theoretical knowledge
with the engineering aspects of lasers. Although not written in the form of a
college textbook, the book might be used in an advanced college course on laser
technology.
The aim was to present the subject as clearly as possible. Phenomeno
logical descriptions using models were preferred to an abstract mathematical
presentation, even though many simplifications had then to be accepted. Re
sults are given in most cases without proof since the author tried to stress the
application of the results rather than the derivation of the formulas. An exten
sive list of references is cited for each chapter to permit the interested reader
to learn more about some particular subject.
This new edition has been updated and revised to include important new
developments, concepts and technologies which have emerged during the last
ten years.
Through a combination of new discoveries, successful implementation of
well-known ideas, and new applications, research, development and engineer
ing of solid-state lasers has greatly intensified during the last decade. Rather
dramatic possibilities have appeared on the horizon which could bring about a
revolutionary change in solid-state laser technology. We are just on the verge
of seeing these technologies emerge into the commercial and military market
place.
The most exciting prospect is that of solid-state laser materials pumped
by laser-diode arrays and including high-efficiency converters. Efficient, com
pact, frequency agile solid-state lasers with average power levels of up to a few
v
hundred watts and covering most of the visible, near- and mid-infrared regime
could become a reality.
The major new developments in solid-state laser engineering which are
described in this new edition are briefly summarized here.
Wavelength tunability: With the discovery of the alexandrite laser, followed
by a number of other tunable lasers such as Ti : sapphire, great progress has
been made, providing a tunable output from solid-state lasers for atmospheric
and spectroscopic studies and for certain military applications.
Improved efficiency: Co-doped laser crystals, such as Cr: Nd: GSGG, which
are highly efficient absorbers of fl.ashlamp radiation have significantly improved
overall system efficiency of flashlamp-pumped lasers. The introduction of Nd:
phosphate glasses which have twice the gain of silicate glasses has helped to im
prove the efficiency of these lasers. The most dramatic impact on efficiency has
come from laser-diode arrays employed as pump sources for solid-state lasers.
Laser-diode pumping always looked attractive but was not practical due to
such technological barriers as low efficiency, low power and short lifetime. The
significant progress made in diode-laser technology, coupled with the emerg
ing technology of linear and planar diode arrays, has removed these former
technological barriers. Diode pumping is now being widely investigated and is
considered by many researchers to be potentially practical even for high-power
lasers.
Increased average power: Old concepts, such as the slab-laser design, have
been revisited and engineering improvements have resulted in systems pro
ducing high average power with good beam quality. In particular, slab lasers
pumped with laser-diode arrays look potentially very attractive.
Improved beam quality: The use of unstable resonators for solid-state lasers
has increased the power extraction at low order modes. Also, optical phase con
jugation employed to correct thermal distortions introduced by laser amplifiers
has been shown to improve beam quality in high average power systems.
Frequency agility: Improved nonlinear materials such as KTP, BBO and
several organic crystals as well as scaling of KDP to very large apertures have
made harmonic processes more attractive as a means of extending the wave
length coverage of solid-state lasers. Also, stimulated Raman scattering is now
being frequently used to shift the wavelength from a laser into a spectral region
not covered by any other system.
Highly coherent systems: Excellent frequency stability and single axial
mode operation of diode-pumped unidirectional ring lasers make it possible
to design coherent Doppler systems in the near-infrared wavelength regime.
Laser Superstructures: The last 10 years have seen the emergence of Nd:
glass laser systems employed for inertial-confinement fusion research with beam
diameters of close to 1 m and unprecedented power and energy levels.
Although this edition has been expanded and updated, the organisation
of the material has not changed compared to the first edition. The topics cov
ered include the optical amplification process, properties of laser materials,
laser oscillators and amplifiers, resonators, pump systems and heat removal,
Q-switches and mode-lockers, nonlinear devices and optical damage.
VI
Omitted from this second edition is the chapter on lasers designed for
specific applications, since many publications are available which deal with the
various uses of lasers in research, industry, medicine and the military.
This book would not have been possible without the many contributions
to the field of laser engineering that have appeared in the open literature and
which have been used here as the basic source material. I apologize to any of my
colleagues whose work has not been acknowledged or adequately represented
in this book.
My special thanks are due to the editor, Dr. H. Lotsch, for his support
and assistance in preparing the new edition for printing.
Neither edition of this book could have been written without the encour
agement, patience and support of my wife Renate.
Herndon, VA Walter Koechner
January 1988
VII
From the Preface to the First Edition
The first decade of solid-state laser technology has seen the development of an
enormous number of lasing materials and a large variety of interesting design
concepts. However, in recent years the technology has matured to a point where
solid-state lasers have reached a plateau in their development.
To a major extent, the growth in importance of solid-state lasers for in
dustrial and military applications and as a general research tool is due to the
improvement in reliability and maintainability of these systems. The practical
advances of these devices had several major consequences: A wealth of appli
cations for solid-state lasers has emerged in materials processing, holography,
rangefinding, target illumination and designation, satellite and lunar ranging,
thermonuclear fusion, plasma experiments, and in general for scientific work
requiring high power densities. Emphasis has shifted from research and innova
tion to cost reduction and system improvement. As a result, a standardization
of the system designs has occurred. [. .. ]
The author is indebted to Dr. M. Stitch and D. Smart who have carefully
read the manuscript and suggested many corrections. A special note of grati
tude for typing the manuscript on a tight schedule goes to Renate Koechner
and Margaret Lochart. Thanks are due to the editor, Dr. H. Lotsch, for his
assistance in preparing the work for printing.
The book is dedicated to my wife Renate, whose encouragement and un
derstanding were a decisive factor in its timely completion. Without her en
couragement and patience the final goal would not have been achieved.
Santa Monica, CA, 1976 Walter Koechner
VIII
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Optical Amplification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Interaction of Radiation with Matter . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Blackbody Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 Boltzmann Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.3 Einstein Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.4 Phase Coherence of Stimulated Emission . . . . . . . . . . . . . . 7
1.3 Absorption and Optical Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.1 Atomic Lineshapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.2 Absorption by Stimulated Transitions . . . . . . . . . . . . . . . . . 13
1.3.3 Population Inversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.4 Creation of a Population Inversion . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4.1 The Three-Level System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4.2 The Four-Level System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.4.3 The Metastable Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.5 Laser Rate Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2. Properties of Solid-State Laser Materials . . . . . . . . . . . . . . . . . . 28
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.1.1 Host Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.1.2 Active Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.2 Ruby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.3 Nd: Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
2.3.1 Nd:YAG . ............... ...................... ....... 48
2.3.2 Nd: Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.3.3 Nd: Cr: GSGG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.3.4 Nd: YLF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.4 _Er: Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.4.1 Er:YAG ............... ............................... 63
2.4.2 Er: Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.5 Tunable Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
2.5.1 Alexandrite Laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.5.2 Ti : Sapphire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
IX