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Solid State Lasers New Developments and Applications NATO ASI Series Advanced Science Institutes Series A series presenting the results of activities sponsored by the NATO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences Plenum Publishing Corporation B Physics New York and London C Mathematical and Physical Sciences Kluwer Academic Publishers D Behavioral and Social Sciences Dordrecht, Boston, and London E Applied Sciences F Computer and Systems Sciences Springer-Verlag G Ecological Sciences Berlin, Heidelberg, New York, London, H Cell Biology Paris, Tokyo, Hong Kong, and Barcelona 1 Global Environmental Change Recent Volumes in this Series Volume 313—Dissociative Recombination: Theory, Experiment, and Applications edited by Bertrand R. Rowe, J. Brian A. Mitchell, and Andr6 Canosa Volume 314 —Ultrashort Processes in Condensed Matter edited by Walter E. Bron Volume 315 —Low-Dimensional Topology and Quantum Field Theory edited by Hugh Osborn Volume 316—Super-Intense Laser-Atom Physics edited by Bernard Piraux, Anne L'Huillier, and Kazimierz Rz$±ewski Volume 317—Solid State Lasers: New Developments and Applications edited by Massimo Inguscio and Richard Wallenstein Volume 318 —Relativistic and Electron Correlation Effects in Molecules and Solids edited by G. L. Malli Volume 319 —Statics and Dynamics of Alloy Phase Transformations edited by Patrice E. A. Turchi and Antonios Gonis Volume 320 —Singular Limits of Dispersive Waves edited by N. M. Ercolani, I. R. Gabitov, C. D. Levermore, and D. Serre Series B: Physics Solid State Lasers New Developments and Applications Edited by Massimo Inguscio Department of Physics and European Laboratory for Nonlinear Spectroscopy, (LENS) University of Florence Florence, Italy and Richard Wallenstein University of Kaiserslautern Kaiserslautern, Germany Springer Science+Business Media, LLC Proceedings of a NATO Advanced Study Institute on Solid State Lasers: New Developments and Applications, held August 31-September 11, 1992, at Elba Island, Tuscany, Italy NATO-PCO-DATA BASE The electronic index to the NATO ASI Series provides full bibliographical references (with keywords and/or abstracts) to more than 30,000 contributions from international scientists published in all sections of the NATO ASI Series. Access to the NATO-PCO-DATA BASE is possible in two ways: —via online FILE 128 (NATO-PCO-DATA BASE) hosted by ESRIN, Via Galileo Galilei, I-00044 Frascati, Italy —via CD-ROM "NATO Science and Technology Disk" with user-friendly retrieval software in English, French, and German (<DWTV GmbH and DATAWARE Technologies, Inc. 1989). The CD-ROM also contains the AGARD Aerospace Database. The CD-ROM can be ordered through any member of the Board of Publishers or through NATO-PCO, Overijse, Belgium. Library of Congress Catalog1ng-1n-PublIcatIon Data NATO Advanced Study Institute on Solid State Lasers New Developments and Applications (1992 Elba, Italy) Solid state lasers new developments and applications / edited by Massimo Ingusdo and Richard Wallensteln. p. cm. — (NATO ASI series. Series B, Physics . v. 317) "Published 1n cooperation with NATO Scientific Affairs Division." Includes bibliographical references and Index. ISBN 978-1-4613-6306-4 ISBN 978-1-4615-2998-9 (eBook) DOI 10.1007/978-1-4615-2998-9 1. Solid-state lasers—Congresses. 2. Laser spectroscopy- -Congresses. 3. Quantum electronics—Congresses. I. Ingusdo, M. II. Wallensteln, Richard. III. North Atlantic Treaty Organization. Scientific Affairs D1v1s1. IV. Title. V. Series. TA1705.N38 1994 621.36'61— dc20 93-38226 CIP Additional material to this book can be downloaded from http://extra.springer.com. ISBN 978-1-4613-6306-4 ©1993 Springer Science+Business Media New York Originally published by Plenum Press, New York in 1993 Softcover reprint of the hardcover 1st edition 1993 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher PREFACE This volume contains the lectures and seminars presented at the NATO Ad vanced Study Institute on "Solid State Lasers: New Developments and Appli cations" the fifteenth course of the Europhysics School of Quantum Electronics, held under the supervision of the Quantum Electronics Division of the European Physical Society. The Institute was held at Elba International Physics Center, Marciana Marina, Elba Island, Tuscany, Italy, August 31 - September 11, 1992. The Europhysics School of Quantum Electronics was started in 1970 with the aim of providing instruction for young researchers and advanced students al ready engaged in the area of quantum electronics or wishing to switch to this area from a different background. Presently the school is under the direction of Professors F.T. Arecchi and M. Inguscio, University of Florence, and Prof. H. Walther, University of Munich, and has its headquarters at the National Insti tute of Optics (INO), Florence, Italy. Each time the directors choose a subject of particular interest, alternating fundamental topics with technological ones, and ask colleagues specifically competent in a given area to take the scientific responsibility for that course. Past courses were devoted to the following topics: 1. 1971: Physical and Technical Measurements with Lasers 2. 1972: Nonlinear Optics and Short Pulses 3. 1973: Laser Frontiers: Short Wavelength and High Powers 4. 1974: Cooperative Phenomena in Multicomponent Systems 5. 1975: Molecular Spectroscopy and Photochemistry with Lasers 6. 1976: Coherent Optical Engineering 7. 1977: Coherence in Spectroscopy and Modern Physics 8. 1979: Lasers in Biology and Medicine 9. 1980: Physical Processes in Laser Material Interactions 10. 1981: Advances in Laser Spectroscopy 11. 1982: Laser Applications to Chemistry 13. 1987: Instabilities and Chaos in Quantum Optics 14. 1989: Applied Laser Spectroscopy The objective of the ASI on "Solid State Lasers: New Developme~ts ~d ~ppli cations" was to bring together young researchers and top level SCIentists In the fields where advanced research and interdisciplinary applications of solid state lasers are being made. A major aim was to illustrate the basic aspects of the new, advanced laser sources as well as the rapidly developing technical applications. It was shown how fascinating and useful can be the transfer of high technology techniques from highly specialized laboratories to a more general use. The scientific organization of the course was taken care of by F.T. Arecchi, University of Florence, R.I. Byer, Stanford University, M. Inguscio, Director of the ASI, University of Florence, R. Wallenstein, University of Kaiserslautern, and H. Walther, University of Munich and MPI for Quantum Optics. v Lectures started with the description of new concept resonators including spe cial designs for high brightness operation. Also, configurations for mode locked operation were discussed as well as monolithic designs and quantum confined resonators. Basic properties and new developments in solid state laser materials were covered also in relation to crystal growth problems and giving emphasis to materials for tunable operation and nonlinear generation. Essentially all solid state lasers were presented in a series of exhaustive lectures. The contributions to the present volume include diode pumped solid state lasers, high power diode lasers, rare earth ion lasers, Yb: Yag or YLF based lasers, color center lasers and fibre lasers. Extension of the spectral coverage by means of optical parametric generation and harmonic generation is also illustrated, while the contribution of solid state lasers to the production of X-ray radiation is discussed. Techniques for coherent improvement and frequency control are discussed in particular in conjunction with semiconductor diode lasers. Selected examples in atomic and molecular spectroscopy, including frequency metrology and environmental analysis, can also be found. There were 16 invited lecturers, 6 seminars speakers and 59 other participants at the Institute. They came from three main different research areas: solid state physics, optics and quantum electronics, atomic and molecular physics. A novelty was constituted by the official participation of researchers from Cen tral and East Europe countries, according to the new rules stated by NATO. Also in this case the participation was very active and a significant exchange of information was possible. The success of the NATO-ASI was also helped by the charming atmosphere of the small village in the Elba Island. We could also take advantage of the logistic support of the Elba International Physics Center and we would like to thank Mrs. Antonella Sapere secretary of the Center. We wish to express our appreciation to the NATO Scientific Affairs Division, whose financial support made the Institute possible. We also acknowledge the contribution of the Consiglio Nazionale delle Ricerche (CNR). The National Science Foundation contributed with two travel grants for USA participants. Additional funding has been provided by NATO national officer for the participation of students from Turkey and Portugal. We wish to thank Mrs. Maria B. Petrone of INO, who, as secretary of the Euro physics School of Quantum Electronics, significantly helped in the organization of this course. Together with the participants, we are grateful to Anna Chiara Arecchi for her competent and enthusiastic assistance during the course. We remember with great pleasure the Quartet (Renzo Pelli - Flute, Warwick Lister - Violin, Anne Lokken - Viola and Ursula Koenig - Violoncello) whose performance of music by Mozart and Haydn was particularly impressive. M.lnguscio R. Wallenstein vi CONTENTS Resonator Designs for High Brightness Solid-State Lasers 1 G. Cerullo, S. De Silvestri, V. Magni and O. Svelto Defining and Measuring Laser Beam Quality 13 A.E. Siegman Mode-Locked Solid State Lasers 29 A.I. Ferguson and G.P.A. Malcolm High Power Rod, Slab, and Tube Lasers 45 U. Wittrock Solid-State Laser Materials: Basic Properties and New Developments 67 G. Huber Quantum Confined Semiconductor Lasers 83 R. Cingolani Diode Pumped Solid State Lasers 99 R.L. Byer Generation of Visible Light with Diode Pumped Solid State Lasers 121 K.-J. Boller, J. Bartschke, R. Knappe and R. 'iV'allenstein High Power Diode Lasers 139 C. Hanke Efficient Narrowband Optical Parametric Oscillators of Beta Barium-Borate (BBO) and Lithium-Triborate (LBO) 157 A. Fix, R. Feldbausch, T. Schroder. R. Urschel and R. Wallenstein Travelling Wave Parametric Generation of Highly Coherent Femtosecond Pulses Tunable from 730 to 3000 nm 167 G.P. Banfi, R. Danielius, P. Di Trapani. F. Foggi, A. Piskarskas, R. Righini and I. Sa 'nta Frequency Conversion of PS-Pulses: Tunable Pulses from the UV to the Near Infrared 179 R. Beigang and A. Nebel vii Quasi-Three-Level Lasers 189 T.Y. Fan Er,Tm,Ho: YLF Lasers in Astigmatically Compensated Resonators 205 P. Minguzzi, A. Di Lieto, H.P. Jenssen and M. Tonelli Color Center Lasers: State of the Art and Recent Developments 221 R. Beigang and Z. Yoon Fibre Lasers 231 D.C. Hanna The Role of Solid State Lasers in Soft-X-Ray Projection Lithography 247 W.T. Silfvast, M.C. Richardson, H. Bender, A. Hanzo, V. Yanovsky, F. Jin and J. Thorpe Second Harmonic Generation and its Application to High Resolution Spectroscopy of Atomic Hydrogen 263 C. Zimmermann, A. Hemmerich and T.W. Hansch Diode Lasers and Metrology 279 R. Fox, G. Turk, N. Mackie, T. Zibrova, S. Waltman, M.P. Sassi, J. Marquardt, A.S. Zibrov, C. Weimer and L. Hollberg Semiconductor Diode Lasers in Atomic Spectroscopy 287 G.M. Tino, M. de Angelis, F. Marin and M. Inguscio Overtone Molecular Spectroscopy with Diode Lasers 303 K. Ernst and F. Pavone Optical Frequency Metrology with Solid State Lasers 313 T. Andreae, W. K()nig, R. Wynands and T.W. Hansch Frequency Stabilized TI:Sapphire Laser for High Resolution Spectroscopy of Atomic Hydrogen 331 M. Weitz, F. Schmidt-Kaler and T.W. Hansch Index 347 viii RESONATOR DESIGNS FOR HIGH BRIGHTNESS SOLID-STATE LASERS G. Cerullo, S. De Silvestri, V. Magni, 0. Svelto Centro di Elettronica Quantistica e Strumentazione Elettronica del CNR Dipartimento di Fisica del Politecnico Piazza L. da Vinci 32 -20133 Milano, Italy 1. INTRODUCTION The generation of diffraction limited beams of high power or energy represents a research field of great interest for many scientific and industrial applications. Laser materials of large volume are available and design procedures for optical resonators with large cross-sectional area fundamental modes, that can exploit the laser medium, are a demanding problem. Stable resonators operating on the fundamental TEMoo mode produce high quality diffraction limited beams; however, the transverse mode dimension and, as a consequence, the extracted energy from the gain medium are generally small. On the other hand, unstable resonators can sustain fundamental modes of wide cross section, but the output beam quality and divergence can be degraded by the spatial profile of the output beam. In this work we consider two resonator designs for the generation of diffraction limited beams of high power, which have been applied to Neodymium lasers. The first concerns dynamically stable resonators of low misalignment sensitivity for continuous wave (c. w.) TEMoo lasers with thermal lensing in the active medium. Two active media are considered, namely Nd:YAG and Nd:YLF. The second resonator design concerns unstable resonators with variable reflectivity output mirrors of super-gaussian reflectivity profile, which have been applied to pulsed Nd: YAG lasers of low and high average power. 2. STABLE RESONATORS FOR C.W. TEMoo MODE OPERATION Multimode laser beams with an average power up to the kilowatt can presently be generated with Nd: YAG lasers. On the contrary, the output power is reduced to few tens of watts when a stable resonator operating in the TEMoo mode is used, mainly because of the small overlapping volume of the TEMoo mode with the active material. To increase the output power with stable resonators, a large volume TEMoo mode is required. However, if appropriate design criteria are not applied, the resonators modes and output power become dramatically sensitive to small perturbations and to the mirror misalignment. The problem is further complicated by the lens effect produced in the laser Solid State Lasers: New Developments and Applications Edited by M. Inguscio and R. Wallenstein. Plenum Press. New York. 1993 rod by pumping. In fact for Nd:YAG the rod dioptric power can reach considerable values even at moderate lamp input power levels (e.g. about 4-5 m-I) and plays a fundamental role in determining the laser performances. In the section 2.1 we present simple guidelines for the design of resonators with an internal variable lens, that represents the pumped rod, in order to obtain large fundamental mode volume and minimum misalignment sensitivity. We also point out the main differences for Nd: YAG and Nd:YLF resonator design. In section 2.2 we present the experimental results obtained with those two active materials. 2.1. RESONATOR DESIGN FOR Nd:YAG AND Nd:YLF LASERS The dioptric power 1If of the thermal lens induced in the laser rod is proportional to the input pump powerI,2: (1) where a is the rod radius and k is a constant depending on the opto-mechanical properties of the laser rod and on the pumping efficiency. A resonator containing a variable lens presents, as function of the dioptric power 1If of the lens, two ranges of optical stability, called stability zones, of the same width t.(1/f). The spot size, w3' of the TEMoo mode (half width at l/e2 of the maximum of the gaussian intensity profile) on the rod reaches, inside each stability zone, a minimum where the resonator is said to be "dynamically stable", since it is insensitive, to the first order, to fluctuations of the variable lens. The value w30 of the spot size at this point is related to the width of the stability zone by the relationship3.4: wio = (2A/7r) / t.(l/f) (2) The spot size w30 can be assumed to be representative of the spot size inside the whole stability zone since the spot size varies slowly with the rod dioptric power, except near the stability limit, where it diverges. Equation (2) shows that the fundamental mode volume inside the laser rod ( cxwio) is inversely proportional to the dioptric power range for which the resonator remains stable. The resonator sensitivity against mirror misalignmentS in one of the stability zones, called zone II, is much higher than in the other and diverges near one of the stability limits; it is therefore crucial to design the resonator so that it works in the other zone, called zone 1. The stability zone of low misalignment sensitivity is characterized by the fact that, at one of its limits, the intracavity lens images the end mirrors on each other. Combining Eqs. (1) and (2) one obtains the range of input power ~Pin for which the resonator is stable6: (3) The quantity (a/W30)2 is the ratio between the cross sections of the rod and of the TEMoo mode. For an optimized resonator the rod should be the limiting aperture. Since for good TEMoo operation the ratio a/W30 must be in the range between 1.2 and 2, a/w30 is approximately a constant and independent of the rod size7,8. Therefore, from Eq. (3) the input power range for which the resonator is stable depends only on the parameter k, that is related to the properties of the laser medium and to the pumping efficiency. Since the pump cavity is usually well optimized it follows that t.P. can be assumed as a figure of merit of the solid state material. Assuming a/W30 = 1.5lfito 1.8 for Nd:YAG one obtains 2
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