Handbook of Laser Wavelengths

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Weber, M. J. “Frontmatter” Handbook of Laser Wavelengths. Ed. Marvin J. Weber Boca Raton: CRC Press LLC, 1999

PERIODIC TABLE OF THE ELEMENTS 1 Group IA

1 H

2

New Notation Previous IUPAC Form CAS Version

IIA

13 IIIB IIIA

14 IVB IVA

15 VB VA

3 Li 6.941 2-1

9.012182 2-2 +1 12 +2

4 Be

+2

5 B

Key to Chart Atomic Number Symbol 1995 Atomic Weight

Mg

22.989770 24.3050 2-8-1 2-8-2 +1 20 +2 19

3 IIIA IIIB

4 IVA IVB

87.62 -18-8-2 +1

56 Ba

+2

21 Sc

+3

5 VA VB

22 Ti

+2 +3 +4

6 VIA VIB

+2 +4

50 Sn

Oxidation States

118.710 -18-18-4

7 VIIA VIIB

8

10.811 2-3

Electron Configuration

9 VIIIA VIII

10

11 IB IB

+3

12 IIB IIB

13 Al

6 C

+2 +4 -4

12.0107 2-4 +3

14 Si

7 N 14.00674 2-5

+2 +4 -4

15 P

26.981538 28.0855 30.973761 2-8-3 2-8-4 2-8-5 +2 31 +3 32 +2 33 +4

+2 24 +2 25 +2 26 +2 27 +2 28 +2 29 +1 30 +3 +3 +3 +3 +3 +3 K Ca Co Ni Cu +2 Zn Ga Ge As +4 Cr +6 Mn +4 Fe +5 +7 39.0983 40.078 44.955910 47.867 50.9415 51.9961 55.845 63.546 65.39 69.723 72.61 74.92160 58.933200 58.6934 -8-8-1 -8-8-2 -8-9-2 -8-10-2 -8-11-2 -8-13-1 -8-13-2 -8-16-2 -8-18-1 -8-18-2 -8-18-3 -8-18-4 -8-18-5 -8-13-2 -8-15-2 +1 38 +2 39 +3 40 +4 41 +3 42 +6 43 +4 44 +3 45 +3 46 +2 47 +1 48 +2 49 +3 50 +2 51 37 +6 +3 54.938049 Rb Sr Y Zr Nb +5 Mo Tc Rh Pd Ag Cd In Sn +4 Sb +7 Ru 85.4678 -18-8-1

18 VIIIA

2 He

+1

55 Cs

17 VIIB VIIA

+1 -1

1.00794 1

11 Na

16 VIB VIA

23 V

88.90585 91.224 92.90638 95.94 (98) 101.07 102.90550 106.42 107.8682 112.411 114.818 118.710 121.760 -18-9-2 -18-10-2 -18-12-1 -18-13-1 -18-13-2 -18-15-1 -18-16-1 -18-18-0 -18-18-1 -18-18-2 -18-18-3 -18-18 -4 -18-18-5 +3 +4 +5 +6 +4 +3 +3 +2 +1 +1 +1 +2 57* 72 73 74 75 76 77 78 79 +3 80 81 82 +4 83 +6 +4 +4 +4 +3 La Hf Ta W Re Ir Pt Au Hg +2 Tl Pb Bi +7 Os

132.90545 137.327 138.9055 178.49 180.9479 -18-8-1 -18-8-2 -18-9-2 -32-10-2 -32-11-2 +1 88 +2 89** +3 104 +4 105 87

183.84 -32-12-2

186.207 -32-13-2

190.23 -32-14-2

192.217 -32-15-2

195.078 -32-17-1

196.96655 200.59 -32-18-1 -32-18-2

107 Bh

108 Hs

109 Mt

110 Uun

111 Uuu

(264) -32-13-2

(269) -32-14-2

(268) -32-15-2

(271) -32-16-2

(272)

Fr

Ra

Ac

Rf

Db

106 Sg

(223) -18-8-1

(226) -18-8-2

(227) -18-9-2

(261) -32-10-2

(262) -32-11-2

(266) -32-12-2

* Lanthanides

58 Ce

+3 +4

140.116 -19-9-2

** Actinides

90 Th

+4

232.0381 -18-10-2

59 Pr

+3

60 Nd

+3

140.90765 144.24 -21-8-2 -22-8-2 +5 92 +3 91 +4 +4 Pa U +5 +6 231.03588 238.0289 -20-9-2 -21-9-2

61 Pm

+3

(145) -23-8-2

93 Np (237) -22-9-2

62 Sm

+2 +3

150.36 -24-8-2 +3 +4 +5 +6

94 Pu (244) -24-8-2

63 Eu

+2 +3

151.964 -25-8-2 +3 +4 +5 +6

95 Am (243) -25-8-2

64 Gd

+3

157 .25 -25-9-2 +3 +4 +5 +6

96 Cm (247) -25-9-2

+3

65 Tb

204.3833 -32-18-3

207.2 -32-18-4

4.002602 2 +1 8 -2 9 -1 10 0 +2 F Ne +3 O +4 +5 -1 18.9984032 20.1797 -2 15.9994 2-7 2-8 -3 2-6 +3 16 +4 17 +1 18 0 +5 +6 +5 -3 S -2 Cl +7 Ar -1 32.066 35.4527 39.948 2-8-6 2-8-7 2-8-8 +3 34 +4 35 +1 36 0 +5 +6 +5 -3 Se -2 Br -1 Kr 78.96 -8-18-6 +3 +5 -3

79.904 -8-18-7

208.98038 -32-18-5

+4 +6 -2

83.80 -8-18-8

+1 54 0 +5 +7 Xe -1 127.60 126.90447 131.29 -18-18-6 -18-18-7 -18-18-8 +3 84 +2 85 0 86 +5 +4

52 Te

K

K-L

K-L-M

-L-M-N

53 I

Po

At

Rn

(209) -32-18-6

(210) -32-18-7

(222) -32-18-8

-M-N-O

-N-O-P

112 Uub -O-P-Q

+3

66 Dy

+3

67 Ho

+3

68 Er

+3

69 Tm

+3

70 Yb

158.92534 162.50 164.93032 167.26 168.93421 173.04 -27-8-2 -28-8-2 -29-8-2 -30-8-2 -31-8-2 -32-8-2 +3 +3 +3 +3 +2 102 97 98 99 100 101 +4 +3

Bk

Cf

Es

Fm

Md

No

(247) -27-8-2

(251) -28-8-2

(252) -29-8-2

(257) -30-8-2

(258) -31-8-2

(259) -32-8-2

+2 +3

71 Lu

+3

174.967 -32-9-2 +2 +3

103 Lr

-N-O-P +3

(262) -32-9-2

The new IUPAC format numbers the groups from 1 to 18. The previous IUPAC numbering system and the system used by Chemical Abstracts Service (CAS) are also shown. For radioactive elements that do not occur in nature, the mass number of the most stable isotope is given in parentheses. References 1. G. J. Leigh, Editor, Nomenclature of Inorganic Chemistry, Blackwell Scientific Publications, Oxford, 1990. 2. Chemical and Engineering News, 63(5), 27, 1985. 3. Atomic Weights of the Elements, 1995, Pure & Appl. Chem., 68, 2339, 1996.

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Shell 0

-O-P-Q

Handbook of Laser Wavelengths Marvin J. Weber Ph.D. Lawence Berkeley National Laboratory University of California Berkeley, California

 1999 by CRC PRESS LLC

© CRC Press 1999 LLC

Foreword It is really amazing how many laser transitions and how many laser wavelengths have been discovered. They cover nearly every class of material, from free electrons through gases, liquids, and solids. It is perhaps even more amazing that the comprehensive listing in this book could be compiled through the collaboration of leading experts in each of the fields. Forty years ago, when Charles Townes and I were first trying to discover how lasers might be made, it seemed very difficult. We had always been taught that the world was pretty close to being in equilibrium, even though masers had shown that you could sometimes get away from it. As Ali Javan pointed out then, when discussing possible gas lasers, there are many processes tending to restore equilibrium. Moreover, since nobody had ever made a laser, we thought it might be very difficult. There might be some hidden problem that we had over-looked. But that turned out to be wrong and some kinds of lasers are quite easy to make once you know how. When thinking of possible laser materials, I for one had plenty of blind spots and poorly based prejudices. For instance, I knew that the optical gain, for a given excess of excited atoms, would be inversely proportional to the spectral linewidth. Thus I felt that narrow lines were essential, overlooking the fact that some broad bands in things like organic dyes have large oscillator strengths and so make up for their large width. Also, for a time I couldn't see why anyone would want to use a laser to pump another, thereby compounding their inefficiencies. Fortunately, lasers attracted the interest and stimulated the imagination of large numbers of very clever people. Some of them had specialized knowledge of things like crystal growing, very hot plasmas, or semiconductor luminescence. From their work have come the very many types of lasers listed in this book. Some of the discoveries resulted from careful study and planning, while others were serendipitous. Many lasers have been discovered but never put to any practical use. In some cases, gases are too corrosive or too easily adsorbed on the walls. In others, crystalline materials are too difficult to grow in useful sizes, or are too hygroscopic. Sometimes, there just isn’t any obvious need for that kind of laser. Perhaps someone browsing in this book will find something for a new use, or will think of ways to overcome the apparent difficulties. Perhaps also in the future, or even now, someone will recognize other blind spots and will see new approaches to yield still more types of useful lasers. Arthur L. Schawlow Stanford University

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Preface Although we are well into the fourth decade since the advent of the laser, the number and type of lasers and their wavelength coverage continue to expand. One seeking a photon source is now confronted with an enormous number of possible lasers and laser wavelengths. In addition, various techniques of frequency conversion—harmonic generation, optical parametric oscillation, sum- and difference-frequency mixing, and Raman shifting—can be used to enlarge the spectral coverage. This volume seeks to provide a comprehensive compilation of the wavelengths of lasers in all media in a readily accessible form for scientists and engineers searching for laser sources for specific applications. The compilation also indicates the state of knowledge and develop-ment in the field, provides a rapid means of obtaining reference data, is a pathway to the literature, contains data useful for comparison with predictions and/or to develop models of processes, and may reveal fundamental inconsistencies or conflicts in the data. It serves both an archival function and as an indicator of newly emerging trends. The Handbook of Laser Wavelengths is derived from data evaluated and compiled by the contributors of Volumes I and II and Supplement 1 of the CRC Handbook Series of Laser Science and Technology. In most cases it was possible to update these tabulations to include more recent additions and new categories of lasers. For semiconductor lasers where in some instances the lasing wavelength may not be a fundamental property but the result of material engineering and the operating configuration, an effort was made to be representative rather than exhaustive in the coverage of the literature. The number of gas laser transitions is huge; they constitute nearly 80% of the over 15,000 laser wavelengths in this volume. Laser transitions in gases are well covered through the late 1980s in the above volumes. An electronic database of gas lasers prepared from the tables in Volume II and Supplement 1 by John Broad and Stephen Krog (Joint Institute of Laboratory Astrophysics) was used for this volume, but does not cover all recent developments. In Section 1, a brief description of various types of lasers is given. Lasers are divided by medium—solid, liquid, and gas—each one of which is further subdivided, as appropriate, into distinctive types. Thus there are sections on crystalline paramagnetic ion lasers, glass lasers, color center lasers, semiconductor lasers, polymer lasers, liquid and solid-state dye lasers, rare earth liquid lasers, and neutral atom, ion, and molecular gas lasers. A separate section on "other" lasers covers lasers having special operating conditions or nature. These include extreme ultraviolet and soft x-ray lasers, free electron lasers, nuclear-pumped lasers, lasers in nature, and lasing without inversion. Brief descriptions of each type of laser are given followed by tables listing reported lasing wavelength, lasing element or medium, host, other experimental conditions, and primary literature citations. All lasers are listed in order of increasing wavelength. The realm of tunable lasers has expanded and includes liquid and solid-state dye lasers, lanthanide and transition-metal crystalline lasers, color center lasers, and semiconductor and polymer lasers. Tuning ranges, when reported, are given for these broadband lasers. For most types of lasers, lasing—light amplification by stimulated

 1999 by CRC PRESS LLC

emission of radiation—includes, for completeness, not only operation in a resonant cavity but also single-pass gain or amplified spontaneous emission (ASE). The wavelengths of lasing transitions are of primary concern. No detailed descriptions of laser structure, operation, or performance are provided. These properties are covered in Volumes I and II and Supplement 1 of the CRC Handbook Series of Laser Science and Technology. Although laser performance data are not tabulated, a special section on commercially available lasers is included to provide a perspective on the current stateof-the-art and performance boundaries (although these are expected to change due to advances in technology). Further background information about lasers in general and about specific types of lasers in particular can be obtained from the books and articles listed under Further Reading in each section. To cope with the continuing and bewildering proliferation of acronyms, abbreviations, and initialisms that range from the clever and informative to the amusing or annoying, two appendices are included—one for types and structures of lasers and amplifiers and one for solid-state laser materials. A third appendix provides a list of fundamental physical constants of interest to laser scientists and engineers. Because lasers now cover such a large wavelength range and because researchers in different fields are frequently accustomed to using different units, there is also a "Rosetta stone for spectroscopists" on the inside back cover. I wish to acknowledge the valuable help and expertise of the Advisory Board for this volume who reviewed the material, made suggestions about the contents, and in several cases contributed material (the Board, however, is not responsible for the accuracy nor thoroughness of the tabulations). We are all indebted to the contributors to Volumes I and II and Supplement 1 of the CRC Handbook Series of Laser Science and Technology who compiled the data from which most of this volume was derived. Others who have provided helpful comments, suggestions, and data include Eric Bründermann, Federico Capasso, Henry Freund, Claire Gmachl, Victor Granatstein, Eugene Haller, Stephen Harris, John Harreld, Thomas Hasenberg, Alan Heeger, Heonsu Jeon, George Miley, Michael Mumma, Dale Partin, Maria Petra, Jin-Joo Song, and Riccardo Zucca. Finally I appreciate the help of the CRC Press staff during the preparation of this volume—Tim Pletscher, Acquiring Editor for Engineering, Felicia Shapiro, Suzanne Lassandro, Gerry Axelrod—and especially Mimi Williams for her careful and excellent editing of the manuscript. Marvin John Weber Danville, California

 1999 by CRC PRESS LLC

The Author Marvin John Weber received his education at the University of California, Berkeley, and was awarded the A.B., M.A., and Ph.D. degrees in physics. After graduation, Dr. Weber continued as a postdoctoral Research Associate and then joined the Research Division of the Raytheon Company where he was a Principal Scientist working in the areas of spectroscopy and quantum electronics. As Manager of Solid State Lasers, his group developed many new laser materials including rare-earth-doped yttrium orthoaluminate. While at Raytheon, he also discovered luminescence in bismuth germanate, a scintillator crystal widely used for the detection of high energy particles and radiation. During 1966 to 1967, Dr. Weber was a Visiting Research Associate with Professor Arthur Schawlow's group in the Department of Physics, Stanford University. In 1973, Dr. Weber joined the Laser Program at the Lawrence Livermore National Laboratory. As Head of Basic Materials Research and Assistant Program Leader, he was responsible for the physics and characterization of optical materials for high-power laser systems used in inertial confinement fusion research. From 1983 to 1985, he accepted a transfer assignment with the Office of Basic Energy Sciences of the U.S. Department of Energy in Washington, DC where he was involved with planning for advanced synchrotron radiation facilities and for atomistic computer simulations of materials. Dr. Weber returned to the Chemistry and Materials Science Department at LLNL in 1986 and served as Associate Division Leader for condensed matter research and as spokesperson for the University of California/National Laboratories research facilities at the Stanford Synchrotron Radiation Laboratory. He retired from LLNL in 1993 but continues as a Participating Guest in the Physics and Space Technology Department. He presently does consulting and is a physicist in the Center for Functional Imaging at the Lawrence Berkeley National Laboratory. Dr. Weber is Editor-in-Chief of the multi-volume CRC Handbook Series of Laser Science and Technology. He has also served as Regional Editor for the Journal of NonCrystalline Solids, as Associate Editor for the Journal of Luminescence and the Journal of Optical Materials, and as a member of the International Editorial Advisory Boards of the Russian journals Fizika i Khimiya Stekla (Glass Physics and Chemistry) and Kvantovaya Elektronika (Quantum Electronics). Among several honors he has received are an Industrial Research IR-100 Award for research and development of fluorophosphate laser glass, the George W. Morey Award of the American Ceramics Society for his basic studies of fluorescence, stimulated emission and the atomic structure of glass, and the International Conference on Luminescence Prize for his research on the dynamic processes affecting luminescence efficiency and the application of this knowledge to laser and scintillator materials. Dr. Weber is a Fellow of the American Physical Society, the Optical Society of America, and the American Ceramics Society and has been a member of the Materials Research Society and the American Association for Crystal Growth.

 1999 by CRC PRESS LLC

Advisory Board John T. Broad, Ph.D. Informed Access Systems, Inc. Boulder, Colorado (formerly of JILA)

David J. E. Knight, Ph.D. DK Research Twickenham, Middlesex , England (formerly of National Physical Laboratory)

Connie Chang-Hasnain, Ph.D. William F. Krupke, Ph.D. Electrical Engineering/Computer Sciences Laser Program University of California Lawrence Livermore National Berkeley, California Laboratory Livermore, California William B. Colson, Ph.D. Physics Department Naval Postgraduate School Monterey, California

Brian J. MacGowan, Ph.D. Laser Program Lawrence Livermore National Laboratory Livermore, California

Christopher C. Davis, Ph.D. Electrical Engineering Department University of Maryland College Park, Maryland

Stephen Payne, Ph.D. Laser Program Lawrence Livermore National Laboratory Livermore, California

Bruce Dunn, Ph.D. Materials Science and Engineering University of California Los Angeles, California

Clifford R. Pollock, Ph.D. School of Electrical Engineering Cornell University Ithaca, New York

J. Gary Eden, Ph.D. Electrical and Computer Engineering University of Illinois Urbana, Illinois

Anthony E. Siegman, Ph.D. Department of Electrical Engineering Stanford University Stanford, California

Alexander A. Kaminskii, Ph.D. Institute of Crystallography Russian Academy of Sciences Moscow, Russia

Richard N. Steppel, Ph.D. Exciton, Inc. Dayton, Ohio

Anne C. Tropper, Ph.D. Optoelectronic Research Centre University of Southhampton Highfield, Southhampton, England

 1999 by CRC PRESS LLC

Contents of previous volumes on lasers from the CRC HANDBOOK OF LASER SCIENCE AND TECHNOLOGY VOLUME I: LASERS AND MASERS FOREWORD — Charles H. Townes SECTION 1: INTRODUCTION 1.1 Types and Comparisons of Laser Sources — William F. Krupke SECTION 2: SOLID STATE LASERS 2.1 Crystalline Lasers 2.1.1 Paramagnetic Ion Lasers — Peter F. Moulton 2.1.2 Stoichiometric Lasers — Stephen R. Chinn 2.1.3 Color Center Lasers — Linn F. Mollenauer 2.2 Semiconductor Lasers — Henry Kressel and Michael Ettenberg 2.3 Glass Lasers — Stanley E. Stokowski 2.4 Fiber Raman Lasers — Roger H. Stolen and Chinlon Lin 2.5 Table of Wavelengths of Solid State Lasers SECTION 3: LIQUID LASERS 3.1 Organic Dye Lasers — Richard Steppel 3.2 Inorganic Liquid Lasers 3.2.1 Rare Earth Chelate Lasers — Harold Samelson 3.2.2 Aprotic Liquid Lasers — Harold Samelson SECTION 4: OTHER LASERS 4.1 Free Electron Lasers 4.1.I Infrared and Visible Lasers — Donald Prosnitz 4.1.2 Millimeter and Submillimeter Lasers — Victor L. Granatstein, Robert K. Parker, and Phillip A. Sprangle 4.2 X-Ray Lasers — Raymond C. Elton SECTION 5: MASERS 5.1 Masers — Adrian E. Popa 5.2 Maser Action in Nature — James M. Moran SECTION 6: LASER SAFETY 6.1 Optical Radiation Hazards — David H. Sliney 6.2 Electrical Hazards from Laser Power Supplies — James K. Franks 6.3 Hazards from Associated Agents — Robin DeVore

 1999 by CRC PRESS LLC

VOLUME II: GAS LASERS SECTION 1: NEUTRAL GAS LASERS — Christopher C. Davis SECTION 2: IONIZED GAS LASERS — William B. Bridges SECTION 3: MOLECULAR GAS LASERS 3.1 Electronic Transition Lasers — Charles K. Rhodes and Robert S. Davis 3.2 Vibrational Transition Lasers — Tao-Yaun Chang 3.3 Far Infrared Lasers — Paul D. Coleman and David J. E. Knight SECTION 4: TABLE OF LASER WAVELENGTHS — Marvin J. Weber

SUPPLEMENT 1: LASERS SECTION 1: SOLID STATE LASERS 1.1 Crystalline Paramagnetic Ion Lasers — John A. Caird and Stephen A. Payne 1.2 Color Center Lasers — Linn F. Mollenauer 1.3 Semiconductor Lasers — Michael Ettenberg and Henryk Temkin 1.4 Glass Lasers — Douglas W. Hall and Marvin J. Weber 1.5 Solid State Dye Lasers — Marvin J. Weber 1.6 Fiber Raman Lasers — Roger H. Stolen and Chinlon Lin 1.7 Table of Wavelengths of Solid State Lasers — Farolene Camacho SECTION 2: LIQUID LASERS 2.1 Organic Dye Lasers — Richard N. Steppel 2.2 Liquid Inorganic Lasers — Harold Samelson SECTION 3: GAS LASERS 3.1 Neutral Gas Lasers — Julius Goldhar 3.2 Ionized Gas Lasers — Alan B. Petersen 3.3.1 Electronic Transition Lasers — J. Gary Eden 3.3.2 Vibrational Transition Lasers — Tao-Yuan Chang 3.3.3 Far-Infrared CW Gas Lasers — David J. E. Knight 3.4 Table of Wavelengths of Gas Lasers — Farolene Camacho SECTION 4: OTHER LASERS 4.1 Free-Electron Lasers — William B. Colson and Donald Prosnitz 4.2 Photoionization-Pumped Short Wavelength Lasers — David King 4.3 X-Ray Lasers — Dennis L. Matthews 4.4 Table of Wavelengths of X-Ray Lasers 4.5 Gamma-Ray Lasers — Carl B. Collins SECTION 5: MASERS 5.1 Masers — Adrian E. Popa 5.2 Maser Action in Nature — James M. Moran

 1999 by CRC PRESS LLC

HANDBOOK OF LASER WAVELENGTHS TABLE OF CONTENTS FOREWORD PREFACE SECTION 1: INTRODUCTION SECTION 2: SOLID STATE LASERS 2.1 Crystalline Paramagnetic Ion Lasers 2.2 Glass Lasers 2.3 Solid State Dye Lasers 2.4 Color Center Lasers 2.5 Semiconductor Lasers 2.6 Polymer Lasers SECTION 3: LIQUID LASERS 3.1 Organic Dye Lasers 3.2 Rare Earth Liquid Lasers SECTION 4: GAS LASERS 4.1 Neutral Atom, Ionized, and Molecular Gas Lasers 4.2 Optically Pumped Far Infrared and Millimeter Wave Lasers 4.3 References SECTION 5: OTHER LASERS 5.1 Extreme Ultraviolet and Soft X-Ray Lasers 5.2 Free Electron Lasers 5.3 Nuclear Pumped Lasers 5.4 Natural Lasers 5.5 Inversionless Lasers SECTION 6: COMMERCIAL LASERS 6.1 Solid State Lasers 6.2 Semiconductor Lasers 6.3 Dye Lasers 6.4 Gas Lasers APPENDICES Appendix 1 Appendix 2 Appendix 3

Abbreviations, Acronyms, Initialisms, and Common Names for Types and Structures of Lasers and Amplifiers Abbreviations, Acronyms, Initialisms, and Mineralogical or Common Names for Solid State Laser Materials Fundamental Constants

 1999 by CRC PRESS LLC

Weber, M. J. “Introduction” Handbook of Laser Wavelengths. Ed. Marvin J. Weber Boca Raton: CRC Press LLC, 1999

 1999 by CRC PRESS LLC

Section 1: Introduction

 1999 by CRC PRESS LLC

Section 1 INTRODUCTION The laser has become an invaluable tool for mankind. The ubiquitous presence of lasers in our lives is evident from their use in such diverse applications as science and engineering, communications, medicine, manufacturing and materials processing, art and entertainment, data processing, environmental sensing, defense, energy, astronomy, and metrology. It is difficult to imagine state-of-the-art physics, chemistry, biology, and medicine research with-out the use of radiation from various laser systems. Laser action occurs in all states of matter—solids, liquids, gases, and plasmas. In this volume lasers are categorized based on the active medium. The spectral output ranges of solid, liquid, and gas lasers are shown in Figure 1.1 and extend from the soft x-ray and extreme ultraviolet regions to millimeter wavelengths, thus overlapping masers. In addition to lasers operating at one or more discrete wavelengths, some are tunable over broad wavelength bands. Using various frequency conversion techniques—harmonic generation, parametric oscillation, sum- and difference-frequency mixing, and Raman shifting—the wavelength of a given laser can be extended to longer and shorter wavelengths. Frequently a laser is used as an excitation source for a second medium that generates new laser wavelengths. The medium in essence acts as a wavelength shifter. Within each category of lasing medium there may be differences in the nature of the active lasing ion or center, the composition of the medium, and the excitation and operating techniques. For some lasers, the periodic table has been extensively explored and exploited; for others—solid-state lasers in particular—the compositional regime of hosts continues to expand. In the case of semiconductor lasers the ability to grow special structures one atomic layer at a time by liquid phase epitaxy, molecular beam epitaxy, and metalorganic chemical vapor deposition has led to numerous new structures and operating configurations, such as quantum wells and superlattices, and to a proliferation of new lasing wavelengths. Ultraviolet Soft x-ray

X-ray

Visible

Vacuum ultraviolet

Infrared

Millimetermicrowave

Far infrared

Gas lasers:

Masers

3.9 nm

Liquid lasers: 0.33 µm

1.8 µm

Solid-state lasers: 0.17 µm

0.001

0.01

0.1

360 µm

1.0

10

100

1000

Wavelength ( µm)

Figure 1.1

Reported ranges of output wavelengths for various laser media.

As will be evident from the brief descriptions below of the different types of lasers covered in this volume, the vitality of the field of lasers is stunning. Furthermore, recent announcements such as those of a single-atom

 1999 by CRC PRESS LLC

laser, 1 lasing without inversion,2 and the use of Bose-Einstein condensates for an atom laser 3 continue to extend our understanding of atomic coherence and interference effects in laser physics and quantum optics.

Solid State Lasers This group includes lasers based on paramagnetic ions, organic dye molecules, and color centers in crystalline or amorphous hosts. Semiconductor lasers are also included in this section because they are a solid state device, although the nature of the active center—recombination of electrons and holes—is different from the dopants or defect centers used in other lasers in this category. The recently emerging field of conjugated polymer lasers is also covered in this section. Solid-state excimer lasers, for which the number of reported cases of lasing is insufficient to warrant a tabulation, are noted at the end of this section. Reported ranges of output wavelengths for various types of solid-state lasers are shown in Figure 1.2. The differences in the ranges of spectral coverage arise in part from the dependence on host properties, in particular the range of transparency and the rate of nonradiative decay due to multiphonon processes. 0.17 µm

7.2 µm

Paramagnetic ions ( 0.38 µm

4.0 µm

Paramagnetic ions ( 0.38 µm

crystal )

glass )

0.87 µm

Organic dyes 0.36 µm

5.0 µm

Color centers 0.33 µm

0.1

360 µm

Semiconductors

1.0

10

100

Wavelength (µm) Figure 1.2

Reported ranges of output wavelengths for various types of solid state lasers.

Crystalline Paramagnetic Ion Lasers The elements that have been reported to exhibit laser action as paramagnetic ions (incompletely filled electron shells) in crystalline hosts are indicated in the periodic table of the elements in Figure 1.3. These are mainly transition metal and lanthanide group ions. Also included are several elements (in italics) for which only gain has been reported (see Table 2.1.3). Typical concentrations of the lasing ion are ≤1%, however for some hosts and ions concentrations up to 100%, so-called stoichiometric lasers, are possible.

 1999 by CRC PRESS LLC

Figure 1.3 Periodic table of the elements showing the elements (shaded) that have been reported to exhibit laser action as paramagnetic ions in crystalline hosts. Gain has been reported for elements shown in italics.

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Nd3 + Ce3+ Ce3+ Tm 3 + Nd3+ Nd3 + Tm 3 + Pr 3+,Tm3+ Er 3 + Tm 3 + Pr 3 + Tm 3 + Pr3 + Pr 3+ ,Tb 3+ Ho3+,Er3 + Er 3+ Sm 3 + Pr 3 + Eu 3 + Er 3 + Pr 3 + Pr 3 + Sm 3+,Tm3+ Er3+ Pr3+,Sm2+,Er3 + Pr3+ Nd 3 + Ho3+ Tm 3 + Er 3 + Pr3 + Pr 3 + Nd 3+,Pm3 + Ho 3 + Er 3 + Ho3+

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Wavelength ( µm)

Figure 1.4a Approximate wavelengths of crystalline lanthanide-ion lasers; exact wavelengths are dependent on the host and temperature and the specific Stark levels involved (see Table 2.1.4).

 1999 by CRC PRESS LLC

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Yb3+ Pr 3 + Pr 3 + Nd 3 + Pm3+ Ho3+ Er 3 + Dy3 + Er 3 + Nd 3 + Ho 3+ Tm3 + Ho3+ Er 3 + Tm3+ Pr 3 + Er 3 + Er3+ Er3+ Ho3+ Nd 3 + Tm3+ Er3 + Ho3+ Ho3+,Tm3 + Dy3+ Er 3 + Ho 3+ Dy3+ Er3 + Pr3 + Ho3+ Dy 3 + Er 3 + Nd3+ Pr3+ Pr 3 +

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Wavelength (µm)

Figure 1 . 4 b Approximate wavelengths of crystalline lanthanide-ion lasers; exact wavelengths are dependent on the host and temperature and the specific Stark levels involved (see Table 2.1.4).

The general operating wavelengths of crystalline lanthanide-ion lasers are given in Figure 1.4 and range from 0.17 µm for the 5d→4f transition of Nd3+ to 7.2 µm for the 4f→4f transition transition between J states of Pr3+. Whereas f→f transitions of the lanthanide ions have narrow linewidths and discrete wavelengths, d→f transitions of these ions and transitions of many iron group ions have broad emission and gain bandwidths and hence provide a degree of tunability. The tuning ranges of several paramagnetic laser ions in different hosts are shown in Figure 1.5; the ranges for explicit host crystals are included in Table 2.1.4. As evident from Figure 1.5, tunable lasers are based almost exclusively on iron transition group elements. Whereas narrow emission lines of Cr3+ in Al2O 3 (ruby) were used for the first demonstration of laser action, broadband emissions of divalent, trivalent, and tetravalent chromium now provide tunable laser radiation throughout much of the 0.7 to 2.5 µm region.  1999 by CRC PRESS LLC

Ce 3+ (LiYF4 ) Sm2 + (SrF2 ) 3 Ti + (Al 2 O 3 ) 3 Cr +(BeAl 2O , LiSrAlF6 )

V 2+ (MgF2) Cr4 + (Mg2 SiO 4) Ni

2+

(MgF2 , MgO) 2 Co + (MgF2 )

0.5

1.0

1.5

2.0

2.5

Wavelength (µm)

Figure 1.5 Reported wavelength ranges of representative tunable crystalline lasers operating at room temperature (see Table 2.1.4 for details).

Over 300 ordered and disordered crystals have been used as hosts for laser ions.4 These include oxide, halide, and, recently, chalcogenide compounds. That so many different crystals of sufficient size and quality necessary to demonstrate laser action have been prepared is testimony to the crystal growers' art and capabilities. Codopant ions are sometimes added to the hosts to improve optical pumping efficiency. These sensitizer ions are included in Table 2.1.4. The field of solid state lasers is large and still amazingly vital. These lasers have been operated pulsed, Qswitched, mode-locked, or cw. Picosecond pulses can be obtained from broadband lasers using various modelocking techniques; femtosecond pulses can be obtained using saturable absorbers. The population inversion necessary for laser action in solid-state lasers has been achieved by optical pumping with flashlamps, cw arc lamps, the sun, or other lasers (electron beam pumping has also been reported). Recent advances in diode laser pumping now provide all solid-state devices that are rugged, compact, and have long lifetimes. As a result, diode-pumped solid-state lasers combined with nonlinear crystals are replacing gas and liquid dye lasers in a number of applications. Upconversion, a concept promoted initially in the late sixties for phosphor displays and demonstrated for solid state lasing in 1971,5 has witnessed a rebirth of interest with the resurgence of diode pumping and has made possible many new lasing transitions and excitation schemes.4 With one or more pulsed lasers as the pumping source, one can establish a population inversion between almost any pair of energy levels of interest and, provided excited state absorption is not dominant, lasing should be achievable, although the result may be neither efficient nor practical. In the case of the thirteen trivalent lanthanide ions, there are 1639 free-ion J states and 192,177 possible transitions between them, yet to date less than 70 have been used, thus one may anticipate the demonstration of many additional lasing transitions and hosts.

 1999 by CRC PRESS LLC

Glass Lasers The past two decades have also witnessed increased activity in glass lasers, both in the form of bulk materials and of fiber and planar waveguides. The former include large neodymium-doped glasses for amplifiers used in lasers for inertial confinement fusion research. Fibers, with their long interaction region, and heavy metal fluoride glasses, with their low vibrational frequencies and hence reduced probabilities for decay by nonradiative processes, have made possible many new lasing transitions and operation at longer wavelengths. These include erbium- and praseodymium-doped fibers for telecommunications and erbium- and thulium-doped lasers for medical applications. Upconversion techniques have also been actively exploited for glass lasers. The wavelengths of glass lasers are shown in Figure 1.6. The wavelength range is less than that of crystals at both the long and short wavelength extrema. The lasing wavelength could be extended to shorter wavelengths using glassy hosts with larger energy gaps such as beryl-lium fluoride and silica. Extension further into the infrared is limited by the vibrational frequencies associated with the glass network formers and nonradiative decay processes. Unlike crystals, which have a unique composition and structure, changes in glass network formers (e. g., silicate, phosphate, borate) and network modifier ions (e. g., alkali, alkaline earths) affect the stimulated emission cross sections, rates of radiative and nonradiative transitions, crystalline field splittings, and inhomogeneous broadening.6 Although trivially small compositional changes might technically constitute a new host material, those listed in Table 2.2.3 are generally characterized by either different compositions or different operating properties. Commercial glasses are identified by their company's designation. The glass type is generally known but the detailed compositions are usually proprietary. Because of site-to-site variations in the local fields in glass, there is a distribution of energy levels and transition frequencies which appear as inhomogeneous broadening and provide tunability. In the small signal regime, laser action can be obtained by tuning across the inhomogeneous linewidth, whereas in the large signal or saturated gain regime spectral hole burning may occur. Examples of reported tuning ranges of lanthanide-ion glass lasers are shown in Figure 1.7.

Solid State Dye Lasers Lasing media based on fluorescing organic dyes may be in the form of solids, liquids, or gases. Although the liquid state is the most familiar and commonly used form, numerous dye-doped solid materials have been reported to lase or exhibit gain in a spectral range extending from the near ultraviolet (376 nm) to the near infrared (865 nm). As shown in Table 2.3.1, a wide diversity of host materials have been utilized. These include various plastics and polymers, organic single crystals, and organic and inorganic glasses. Solid state dye lasers also include—in a somewhat more exotic vein—edible lasers7 and lasing in animal tissue.8 Although the first reports of solid state dye lasers date back to the 1960s, photo-degradation of the dye has been a serious limitation to the utilization of these lasers. Recently there has been a revival of interest in these lasers, principally because materials exhibiting useful lifetimes and tunable laser action have been identified. A solid state dye laser is now offered commercially (see Table 6.1.1).

 1999 by CRC PRESS LLC

0.1

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Nd 3 + Nd3+ Tm3+ Tm 3 + Pr 3 + Pr 3 + Tb3+ Er 3+ , Ho3+ Pr 3 + Pr 3 + Sm 3 + Pr 3 + Pr 3 + Ho 3 + Tm3+ Er 3+ Pr 3 + Pr 3 + Pm 3 + Nd 3 + Er 3 + Yb3 + Nd 3 + Pr 3 + Pm 3 + Ho 3+ Pr 3 + Nd3+ Ho3+ Tm3+ Tm 3 + Er 3 + Er 3 + Er 3 + Tm 3 + Ho 3 + Tm3+ Er 3 + Ho 3 + Ho 3 + Er 3 + Ho3+

0.1

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Wavelength (µm)

Figure 1 . 6 Approximate wavelengths of lanthanide-ion glass lasers; exact wavelengths are dependent on the glass composition and temperature and the specific Stark levels involved (see Table 2.2.3).

Color Center Lasers Color center lasers have been reported that operate in the wavelength range from approximately 0.4 to 5 µm. The optically active centers in these lasers are various types of point defects (i. e., color centers) in alkali halide and oxide crystals. The color centers are  1999 by CRC PRESS LLC

0.5

1.0 3+

Ho

Tm

1.5

2.0

2.5

3.0

fluorozirconate 3+

fluorozirconate Pr 3+

Er

3+

fluorozirconate

fluorozirconate

Nd 3+ silica Pr

3+

silica 3+

Yb Nd

silica

3+

silica Nd3+ fluorozirconate Tm

Er

3+

3+

fluorozirconate

silica

Tm 3+ silica (Al) Tm

3+

fluorozirconate Ho3+ silicate Tm 3+ fluorozirconate Er

3+

fluorozirconate

Ho3+ fluorozirconate

0.5

1.0

1.5

2.0

2.5

3.0

Wavelength (µm) Figure 1.7

Reported tuning ranges of lanthanide-ion glass lasers (see Table 2.2.3).

generally produced by ionizing radiation or are thermally induced. Additional ions may be present to stabilize the defect center and are included in the description of the active center in Table 2.4.1. Other lasers in this category are based on vibrational transitions of molecular defects, such as CN-. Color center lasers are usually excited by optical pumping with broadband or laser radiation. Lasing involves allowed transitions between electronic energy levels, hence the gain can be high. Due to their large homogeneous emission bandwidths, color center lasers have varying degrees of tunable. The tuning ranges of some of the longer-lifetime color center lasers are shown in Figure 1.8. The output of color center lasers may be cw or pulsed. As in the case of paramagnetic ion lasers, picosecond pulses can be obtained using various mode-locking techniques and femtoseconds pulses using saturable absorbers. The operative lifetimes of the color centers in these lasers depend on the temperature and can vary from hours to months. Many color center lasers require operation at low temperatures.

 1999 by CRC PRESS LLC

RbCl:Li + F (II) A

KCl:I F A(II) KCL:Na FB (II) + KCl:Li (F ) A

+ KCl:Na (F )

2 AH

KCl

N

2

+ NaF F2 1.0

2.0

3.0

4.0

Wavelength (µm)

Figure 1.8

Reported tuning ranges of representative color center lasers (see Table 2.4.1).

Semiconductor Lasers Laser action in semiconductor diode lasers, in contrast to other solid state lasers, is associated with radiative recombination of electrons and holes at the junction of a n-type material (excess electrons) and a p-type material (excess holes). Excess charge is injected into the active region via an external electric field applied across a simple p-n junction (homo-junction) or in a heterostructure consisting of several layers of semiconductor materials that have different band gap energies but are lattice matched. Heterostructure enables highly efficient radiative recombination of electrons and holes by confining them into the smaller band gap material sandwiched between higher band gap materials. This has been the most important step in achieving cw operation of diode lasers at room temperature. Excitation of semiconductor lasers has also been achieved by optical pumping and electron beam pumping. The ability to grow special structures one atomic layer at a time by liquid phase epitaxy (LPE), molecular bean epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) has led to an explosive growth of activity and numerous new laser structures and configurations. When dimensions become