This monograph undertakes to present systematically the methods for solving inverse problems of lidar sensing of the atmosphere, with emphasis on lidar techniques that are based on the use of light scattering by aerosols. The theory of multi-frequency lidar sensing, as a new method for studying the microphysical and optical characteristics of aerosol formations, is also pre sented in detail. The possibilities of this theory are illustrated by the experimental results on microstructure analysis of tropospheric and low stratospheric aerosols obtained with ground-based two- and three-frequency lidars. The lidar facilities used in these experimental studies were construc ted at the Institute of Atmospheric Optics S8 USSR Academy of Sciences. Some aspects of remote control of dispersed air pollution using lidar systems are also considered. A rigorous theory for inverting the data of polarization lidar measure ments is discussed, along with its application to remote measurement of the complex index of refraction of aerosol substances and the microstructure pa rameters of background aerosols using double-ended lidar schemes. Solutions to such important problems as the separation of contributions due to Rayleigh molecular and Mie-aerosol light scattering into the total backscatter are ob tained by using this theory. Lidar polarization measurements are shown to be useful in this case. The efficiency of the methods suggested here for inter preting the lidar polarization measurements is illustrated by experimental results on the investigation of the microphysical parameters of natural aero sols and artificial smokes using polarization nephelometers.

Most of the texts available on lasers deal with laser engineering and laser applications, only a few of them treating theoretical aspects of the laser at an advanced level. Introduction to Laser Physics provides an introduction to the essential physics of quantum electronics and lasers. Fundamental topics in modern optics, the applicability of various theoretical approaches, and the physical meaning of laser-related phenomena are carefully described. Experimental results and properties of practical lasers are interwoven, thereby allowing an explicit demonstration of the rate equation approach and the semiclassical treatment. The basic concepts of nonlinear optical devices and laser spectroscopy are intro- duced. The second edition includes additional information on optical resonators, minor improvements of the text and several new problems, completed with solutions.

There have been two major review articles on the iodine laser in the last ll seven years, liThe Photochemical Iodine Laser by K. Hohla and K. Kompa (Handbook of Chemical Lasers, edited by R. Gross and J. Bott, Wi 1 ey, New York,1976) and a SANDIA report (No. 78-1071, 1978) entitled liThe Atomic Iodine Laserll. Since then, a large body of new material has been published, and practical experience has been gained with large iodine laser systems in Garchi ng (ASTERIX II I) and in the USSR. These 1 asers have now become very reliable tools, especially in fusion-oriented plasma experiments, which represent their main field of application. They can deliver powers in excess of many terawatts per beam and are thus also suited for use in other areas such as X-ray lasers, incoherent X-ray sources, compression of matter and its behaviour at very high densities. The physics of the iodine laser is now rather well understood, and its technology has reached a standard adequate for the construction of large scale systems in the multi-hundred kJ range. In view of this new situation, we thought it useful to document the present state of the art ina book. Its contents and the literature cited therein have been chosen to cover those areas which are of main concern in the design and operation of pulsed high-power iodine lasers.

It was a greatest pleasure for me to learn that Springer-Verlag wished to produce a second edition of my book. In this connection, Dr. H. Lotsch asked me to send hirn a list of misprints, mistakes, and inaccuracies that had been noticed in the first edition and to make corresponding corrections without disturbing the layout or the typo graphy too much. I accepted this opportunity with alacrity and, moreover, found some free places in the text where I was able to insert some concise, up-to-date information about new lasing compounds and stimulated emission channels. It was also possible to increase the number of reference citations. The reader of the second edition hence has access to more complete data on insulating laser crystals. However, sections on laser-crystal physics have not been updated, because a satisfactory de scription of the progress made in the last ten years in this field would have required the sections to be extended enormously or even a new book to be written. Moscow, July 1989 ALEXANDER A. KAMINSKII Preface to the First Edition The greatest reward for an author is the feeling of satisfaction he gets when it becomes c1ear to hirn that readers find his work useful. After my book appeared in the USSR in 1975 I received many letters from fellow physicists inc1uding colleagues from Western European countries and the USA.

The Eighth International Conference on Laser Spectroscopy (EICOLS '87) was held at the Sunwing Hotel in A.re, Sweden, June 22-26; 1987. Fol lowing the traditions ef its predecessors at Vail, Megeve, Jackson Lake, Rottach-Egern, Jasper Park, Interlaken and Maui the intent of EICOLS '87 was to provide a forum for active scientists to meet in an informal at mosphere to discuss recent developments in laser spectroscopy. The scenic and remote location of the conference venue greatly stimulated a lively and relaxed exchange of information and ideas. The conference was attended by 227 scientists from 20 countries includ ing Australia, Austria, Canada, the People's Republic of China, Denmark, Finland, France, the Federal Repulic of Germany, Israel, Italy, Japan, The Netherlands, New Zealand, Norway, Poland, the Soviet Union, Sweden, Switzerland, the United Kingdom and the United States. The scientific program included 14 topical sessions with 50 invited talks, ranging in length from 20 to 40 minutes. About 70 additional in vited contributions were presented in two evening poster sessions. A third evening session included 4 oral and 18 poster post-deadline presentations.

The invention ofthe laser 25years ago resulted in powerfullight sources which led to the observation of unexpected and striking phenomena. New fields of science such as holography and nonlinear optics developed constituting the basis of this volume. The classical principle of linear superposition of light wavesdoes not hold anymore. Two laser beams crossing in a suitable material may produce a set of new beams with different directions and frequencies. The interaction of light waves can be understood by considering the optical grating structures which develop in the overlap region. The optical properties of matter become spatially modulated in the interference region of two light waves. Permanent holographic gratings have been produced in this way by photographic processes for many years. In contrast, dynamic or transient gratings disappear after the inducing light source, usually a laser, has been switched off. The grating amplitude is controlled by the light intensity. Dynamic gratings have been induced in a large number ofsolids, liquids, and gases, and are detected by diffraction, 'forced light scattering' of a third probing beam, or by self-diffraction of the light waves inducing the grating. The combined interference and diffraction effect corresponds to four-wave mixing (FWM) in the language of nonlinear optics. The process is called degenerate ifthe frequenciesofthe three incident wavesand the scattered wave are equal. Degenerate four-wave mixing (DFWM) is a simple method to achieve phase conjugation, i.e. to generate a wave which propagates time reversed with respect to an incident wave.