The chapters of this volume represent the invited papers delivered at the 3rd International Conference on Multiphoton Processes (ICOMP III) held in Iraklion, Crete, Greece, September 5-11, 1984. The invited papers at a conference like ICOMP cannot possibly cover the whole field which has grown to immense proportions in recent years, overlapping with such diverse areas as atomic and molecular spectroscopy, plasma physics, nonlinear optics, quantum optics, etc. We believe these contributions represent that part of the research activity which has been attracting the most interest in the past year or so, as well as reviews of some of the more established topics. Even within this scope, and given the confines imposed by the fi nite duration of a conference, important and timely topics are inevitably left out. But then, there will be ICOMP IV. The collection of articles in this volume, combined with extensive ref erences to related work given by the authors, should provide an introduc tion to the major problems of the field and its state of the art. The chapters have been arranged according to thematic proximity, beginning with atoms, and continuing on with molecules and surfaces. This classi fication, however, would not cover all the subject matter even within the limited scope of the conference and of this volume."

The Tenth International Conference on General Relativity and Gravitation (GR10) was held from July 3 to July 8, 1983, in Padova, Italy. These Conferences take place every three years, under the auspices of the International Society on General Relativity and Gravitation, with the purpose of assessing the current research in the field, critically discussing the prog ress made and disclosing the points of paramount im portance which deserve further investigations. The Conference was attended by about 750 scientists active in the various subfields in which the current research on gravitation and general relativity is ar ticulated, and more than 450 communications were sub mitted. In order to fully exploit this great occur rence of experience and creative capacity, and to pro mote individual contributions to the collective know ledge, the Conference was given a structure of work shops on the most active topics and of general sessions in which the Conference was addressed by invited speakers on general reviews or recent major advance ments of the field. The individual communications were collected in a two-volume publication made available to the participants upon their arrival and widely distributed to Scientific Institutions and Research Centres."

A NATO Advanced Research Workshop on Strongly Coupled Plasma Physics was held on the Santa Cruz Campus of the University of California, from August 4 through August 9, 1986. It was attended by 80 participants from 13 countries, 45 of whom were invited speakers. The present volume contains the texts of the invited talks and many of the contributed papers. The relative length of each text is roughly proportional to the length of the workshop presentation. The aim of the workshop was to bring together leading researchers from a number of related disciplines in which strong Coulomb interactions play a dominant role. Compared to the 1977 meeting in Orleans-la-Source, France and the 1982 meeting in Les-Houches, France, it is apparent that the field of strongly coupled plasmas has expanded greatly and has become a very significant field of physics with a wide range of applications. This workshop had a far greater participation of experimental researchers than did the previous two, and some confrontations of real experiments with theoretical calculations occurred. In the two earlier meetings the theoretical presentations were dominated by numerical simulations of static and dynamic properties of various strongly coupled plasmas. The dearth of experiments in the 1970's is now replaced by some very good experimental efforts.

The present volume contains contributions presented at the NATO Advanced Study Institute on Molecular Ions held on the island of Kos, Greece, from September 30 to October 10, 1980. The meeting was attended by some 60 participants from 15 different countries. It was the first meeting devoted exclusively to the topic of molecular ions. Its vitality derived from bringing together experts and students from a wide variety of disciplines, whose studies bear upon the structure of molecular ions. The aim of the meeting was to assemble these scientists, representing many countries in Europe and North America, to discuss the advances and capabilities of the various experimental and theoretical approaches and to point out un solved problems and directions for future research. The format, in volving lecturers and students, served as a tutorial. Molecular ions play an important role in very diverse fields of nature such as reactions in the ionosphere, the processes of forma tion of molecules in dense interstellar clouds, and the magnetohydro dynamics of plasmas used for energy generation. Our understanding of the properties of molecular ions, their electronic and geometric structures, has been developing from a variety of sources, as far removed as tickling ions with radiofre quency radiation and smashing them apart at relativistic energies. Various laser techniques are described, and the queen of structural determination, spectroscopy, is well represented. On the instrumen tal side, older techniques have been perfected and new methods have evolved."

H. KLEINPOPPEN AND J. F. WILLIAMS It has only very recently become possible to study angular correlations and coherence effects in different areas of atomic collision processes: These investigations have provided us with an analysis of experimental data in terms of scattering amplitudes and their phases, of target parameters such as orientation, alignment, and state multipoles, and also of coherence parameters (e. g., the degree of coherence of excita tion). In this way the analysis of electron-photon, ion-photon, atom-photon, or electron-ion coincidences from electron-atom, ion-atom, or atom-atom collisional excitation has led to a breakthrough such that the above quantities represent most crucial and sensitive tests for theories of atomic collision processes. Similarly, the powerful (e, 2e) experiments (electron-electron coincidences from impact ionization of atoms) have attracted much attention where improved experimental studies and detailed theoretical description provide a wealth of information on either the col lisional ionization process or the atomic structure of the target atom. Interference effects, many-electron correlations, and energy and angular momen tum exchange between electrons in a Coulomb field playa decisive role in the under standing of postcollision interactions. New results on coherence effects and orienta tion and alignment in collisional processes of ions with surfaces and crystal lattices show links to relevant interference phenomena in atomic collisions. In small-angle elastic electron-atom scattering the effect of angular coherence can be studied in a crossed beam experiment."

The energy of a molecule can be studied with the help of quantum theory, a satisfactory approach because it involves only basic and clearly identified physical concepts. In an entirely different approach, the molecular energy can be broken down into individual contributions reflecting chemical bonds plus a host of subsidiary "effects," like y-gauche, skew pentane, ring-strain, etc., giving an overall picture in terms of topological characteristics. The latter approach can be successful, particularly if a sufficient number of particular topological situations have been parametrized (which is an empir ical way of "understanding" chemistry), but also contains the seed for difficulties. Indeed, the danger exists of unduly ascribing a physical meaning to corrective terms whose function is primarily to account in an empirical fashion for discrepancies between "expected" and observed results. The link between this type of empirical approach and the knowledge that the ground state energy is uniquely determined by the electron density is lost somewhere along the road, although some of the "steric effects" are here and there vaguely traced back to electronic effects. The approach presented in this monograph goes back to the fundamen tals in that it is exclusively based on interactions involving nuclear and electronic charges. Confining the study to molecules in their equilibrium geometry, the problem of molecular energies is reduced to its electrostatic aspects, explicitly involving local electron populations."

This volume presents the contributions of participants in the Symposium on Swarm Studies and Inelastic Electron-Molecule Collisions, held on July 19-23, 1985, in Tahoe City, California. This was a joint meeting of the Fourth International Swarm Seminar and the Electron-Molecule Collisions Symposium which have been traditionally separate satellite symposia to the International Conference on the Physics of Electronic and Atomic Collisions (ICPEAC). In the early stages of planning for these two satellite symposia to the XIVth ICPEAC, a group of us recognized the significant scientific merit and advantages of having a joint symposium. This idea was particularly appealing due to a large mutual interest in important advances (theoretical, experimental, and modeling) in both fields, and because it provides a forum to bring together a single-collision point of view with a multiple-collision one. For example, studies of multiple-term solutions to Boltzmann's equation and their application to swarm systems are intrinsically coupled to the availability of both integral and differential cross-sections for electron-molecule collisions. In tum, experimental and theoretical studies of these electron-molecule scattering cross-sections are becoming quite sophisticated, accurate, and comprehensive. Furthermore, in swarm studies, computational and experimental methods have advanced to the point where detailed and meaningful comparison with, and use of, single-collision beam data is now possible. More over, recent experimental advances in the study of single-collision electron at tachment phenomena have provided a significant overlap with swarm data and extension to subthermal energies."

The measurement of spin-polarization observables in reactions of nuclei and particles is of great utility and advantage when the effects of single-spin sub-states are to be investigated. Indeed, the unpolarized differential cross-section encompasses the averaging over the spin states of the particles, and thus loses details of the interaction process. This introductory text combines, in a single volume, course-based lecture notes on spin physics and on polarized-ion sources with the aim of providing a concise yet self-contained starting point for newcomers to the field, as well as for lecturers in search of suitable material for their courses and seminars.

A significant part of the book is devoted to introducing the formal theory-a description of polarization and of nuclear reactions with polarized particles. The remainder of the text describes the physical basis of methods and devices necessary to perform experiments with polarized particles and to measure polarization and polarization effects in nuclear reactions. The book concludes with a brief review of modern applications in medicine and fusion energy research. For reasons of conciseness and of the pedagogical aims of this volume, examples are mainly taken from low-energy installations such as tandem Van de Graaff laboratories, although the emphasis of present research is shifting to medium- and high-energy nuclear physics. Consequently, this volume is restricted to describing non-relativistic processes and focuses on the energy range from astrophysical energies (a few keV) to tens of MeV. It is further restricted to polarimetry of hadronic particles."

The 35th Annual Denver Conference on Applications of X-Ray Analysis was held August 4-8, 1986, on the campus of the University of Denver. Since the previous year's conference had emphasized x-ray diffraction, this year the Plenary Session spotlighted x-ray fluorescence, with the title "Trends in XRF: A World Perspective," featuring renowned speakers from three major areas. XRF IN NORTH AMERICA, by Prof. D. E. Leydon, from Colorado State University, dealt specifically with developments in the fields of instrumentation, data treatment and applications in that part of the world. Prof. H. Ebel, from the Technical University of Vienna, discussed XRF IN EUROPE, concentrating on subjects including total reflection, improved fundamental parameters, quantitation without standards and imaging techniques. Tomoya Arai, of the Rigaku Industrial Corporation in Japan, in considering XRF IN THE FAR EAST, described the scientific activity in XRF and the applications thereof, primarily in Japan and China. These plenary lectures were interspersed with short discussions of PERSONAL OBSERVATIONS on the subject by the co-chairmen of the SeSSion, Ron Jenkins and myself. The intent of this session was to bring the audience up-to-date on the status of the field in various parts of the world, and to give some feeling concerning where it is likely to go in the immediate future. Hopefully, the publication of the written versions of those presentations in this volume will make the authors' thoughts available to many who could not be present at the conference.

The last decade has seen a rapid development and growing importance in the application of nuclear physics methods to material sciences. It is a general desire to understand modern material problems on a microscopic scale, which, due to their inherent microscopic nature, made nuclear techniques highly suitable tools for basic and applied research in this field. The Advanced Study Institute on "Nuclear Physics Applications on Ma terials Science" brought together scientists active in different but closely re lated fields to review and discuss selected topics of bulk properties of metals, semiconductors and insulators as well as properties of surfaces, interfaces and thin films. Most of the excellent lectures and oral presentations of the School are collected in part I of the present volume, while extended abstracts of scientific work presented as posters are added in part II. The pleasant site of the ASI at Viana do Castelo and the northern province of Portugal, Alto Minho, provided the stimulating atmosphere for an in spiring School. Many people contributed to the scientific and social success of the institute. Thanks are especially due to the members of the local organizing committee, N. Ayres de Campos, M. Fernanda da Silva, A. Pedroso de Lima and my co-director J. Carvalho Soares. His permanent involvement in preparing and realization of the ASI was essential for this memorable School.

Recent experimental and theoretical progress has elucidated the tunable crossover, in ultracold Fermi gases, from BCS-type superconductors to BEC-type superfluids.

"The BCS-BEC Crossover and the Unitary Fermi Gas" is a collaborative effort by leading international experts to provide an up-to-date introduction and a comprehensive overview of current research in this fast-moving field.

It is now understood that the unitary regime that lies right in the middle of the crossover has remarkable universal properties, arising from scale invariance, and has connections with fields as diverse as nuclear physics and string theory.

This volume will serve as a first point of reference for active researchers in the field, and will benefit the many non-specialists and graduate students who require a self-contained, approachable exposition of the subject matter.

"

Computation is essential to our modern understanding of nuclear systems. Although simple analytical models might guide our intuition, the complex ity of the nuclear many-body problem and the ever-increasing precision of experimental results require large-scale numerical studies for a quantitative understanding. Despite their importance, many nuclear physics computations remain something of a black art. A practicing nuclear physicist might be familiar with one or another type of computation, but there is no way to systemati cally acquire broad experience. Although computational methods and results are often presented in the literature, it is often difficult to obtain the working codes. More often than not, particular numerical expertise resides in one or a few individuals, who must be contacted informally to generate results; this option becomes unavailable when these individuals leave the field. And while the teaching of modern nuclear physics can benefit enormously from realistic computer simulations, there has been no source for much of the important material. The present volume, the second of two, is an experiment aimed at address ing some of these problems. We have asked recognized experts in various aspects of computational nuclear physics to codify their expertise in indi vidual chapters. Each chapter takes the form of a brief description of the relevant physics (with appropriate references to the literature), followed by a discussion of the numerical methods used and their embodiment in a FOR TRAN code. The chapters also contain sample input and test runs, as well as suggestions for further exploration."

This textbook is for a course in advanced solid-state theory. It is aimed at graduate students in their third or fourth year of study who wish to learn the advanced techniques of solid-state theoretical physics. The method of Green's functions is introduced at the beginning and used throughout. Indeed, it could be considered a book on practical applications of Green's functions, although I prefer to call it a book on physics. The method of Green's functions has been used by many theorists to derive equations which, when solved, provide an accurate numerical description of many processes in solids and quantum fluids. In this book I attempt to summarize many of these theories in order to show how Green's functions are used to solve real problems. My goal, in writing each section, is to describe calculations which can be compared with experiments and to provide these comparisons whenever available. The student is expected to have a background in quantum mechanics at the level acquired from a graduate course using the textbook by either L. I. Schiff, A. S. Davydov, or I. Landau and E. M. Lifshiftz. Similarly, a prior course in solid-state physics is expected, since the reader is assumed to know concepts such as Brillouin zones and energy band theory. Each chapter has problems which are an important part of the lesson; the problems often provide physical insights which are not in the text. Sometimes the answers to the problems are provided, but usually not.

The field of reactive intermediates has been blossoming at a rapid rate in recent years and its impact on chemistry, both "pure" and "applied," as well as on biology, astronomy, and other areas of science, is enormous. Several books have been published which cover the area; one, edited by McManus, * surveys the subject in general at the senior undergraduate or beginning graduate level. In addition, a number of monographs have appeared which deal with individual topics such as carbenes, nitrenes, free radicals, carbanions, carbenium ions, and so on, in great depth. Our objective is somewhat different. We hope that these Advances in . . . type of volumes will appear at irregular intervals of a year to 18 months each. We intend to publish up-to-date reviews in relatively new areas of the chemistry of reactive intermediates. These will be written by world authorities in the field, each one of whom will give the reader a current in-depth review of all aspects of the chemistry of each of these species. It is our plan that the subjects to be reviewed will cover not only organic chemistry but also inorganic, physical, bio-, industrial, and atmospheric chemistry. The volumes themselves, we hope, will end up being reasonably interdisciplinary, though this need not and probably will not be the case for the individual reviews.

The appreciable evolution of the nearly teenaged branch of atomic and molecular physics called beam foil spectroscopy is clearly depicted in the present volumes, which are devoted to publication of presentations at the Fourth International Conference on Beam Foil Spectroscopy and Heavy Ion Atomic Physics Symposium. The transition from childhood to adolescence parallels human experience in that diffusion of interests and interactions beyond the confines of the original family has most certainly occurred. The pre-occupation with techniques and their develop ment has been largely replaced by interest in the physics of the widest possible array of atomic and molecular physics experiments, in which spectroscopic study (visible, UV, XUV, X-ray, electron) of collisional interactions of fast beams is the unifying theme. The description "accelerator-based atomic physics" is perhaps more representative of the subject today than is the original, beam-foil spectroscopy," since so many experiments have nothing to do with foils, and furthermore, employ spectroscopy mainly as an incidental tool. What, then distinguishes beam-foil spectro scopy from overlapping fields of atomic collisions physics? In an era where the boundaries are becoming ever more diffuse, there can be no clear definition. A good functional definition was recently conceived by Peter Erman, under the salubrious stimulus of a large Tennessee bourbon: it is the tribal experience of the community of scientists who have banded together to develop the discipline over the past dozen years, as shared at the triennial conferences devoted to it."

In this Supplement we have collected the invited and contributed talks pre sented at the XVIII European Conference on Few-Body Problems in Physics, organised by the Jozef Stefan Institute and the University of Ljubljana, Slove nia. The Conference, sponsored by the European Physical Society, took place at the lakeside resort of Bled from 8 to 14 September, 2002. This meeting was a part of the series of European Few-Body Conferences, previously held in Evora/Portugal (2000), Autrans/France (1998), Peniscola/Spain (1995), ... Our aim was to emphasise, to a larger extent than at previous Conferences, the interdisciplinarity of research fields of the Few-Body community. To pro mote a richer exchange of ideas, we therefore strived to avoid parallel sessions as much as possible. On the other hand, to promote the participation of young scientists who we feel will eventually shape the future of Few-Body Physics, we wished to give almost all attendees the opportunity to speak."

The International Conference on "Nuclear Structure Study with Neutrons" or ganized in Budapest between 31st July and 5th August. 1972. was the successor of a meeting held seven years ago in Antwerp. The close links between the two conferences were revealed not in name alone but. more importantly. in the choice of subjects discussed. As in Antwerp. the lectures and contributions to the Budapest Conference could be grouped under the following five main headings: nuclear spectroscopy; the optical model; the statistical model and intermediate structures; the mechanism of neutron capture and non-statistical effects; and, finally. miscellaneous special topics. The invited papers on the one hand summarizing recent developments and current thinking in one of the above main topics. and the other surveying the most important results of the contributed papers submitted to the Conference. were presented on the plenary sessions. Most of the contributed papers were read in full on three parallel sessions. This volume contains the complete text of all the lectures delivered in the plenary sessions and abstracts of the contributed papers. The invited talks were presented at the Conference in a rather random order because of technical reasons, it seemed. however, more sensible to change their order according to their subjects and to print them grouped under the above main headings. Further more we divided the Proceedings into two main parts, the first containing only the lectures of summarizing character. the second including the abstracts of the contributions together with the surveying talks."

H. J. BEYER AND H. KLEINPOPPEN We are pleased to present Part D of Progress in Atomic Spectroscopy to the scientific community active in this field of research. When we invited authors to contribute articles to Part C to be dedicated to Wilhelm Hanle, we received a sufficiently enthusiastic response that we could embark on two further volumes and thus approach the initial goal (set when Parts A and B were in the planning stage) of an almost comprehensive survey of the current state of atomic spectroscopy. As mentioned in the introduction to Parts A and B, new experimental methods have enriched and advanced the field of atomic spectroscopy to such a degree that it serves not only as a source of atomic structure data but also as a test ground for fundamental atomic theories based upon the framework of quantum mechanics and quantum electrodynamics. However, modern laser and photon correlation techniques have also been applied successfully to probe beyond the "traditional" quantum mechanical and quantum electrodynamical theories into nuclear structure theories, electro weak theories, and the growing field of local realistic theories versus quan tum theories. It is obvious from the contents of this volume and by no means surprising that applications of laser radiation again played a decisive role in the development of new and high-precision spectroscopic techniques."

The members of the organising Committee and their colleagues have, for many years been investigating the evol ution of the fas'cinating surface features which develop during sputtering erosion of solids. Such experimental, theoretical and computational studies have also been carried out in many international laboratories and, as well as much cow onality and agreement, substantial disagreements were unresolved. In view of the increasing importance of such processes in technological applications such as microlitho graphic etching for the patterning of solid state devices and in fusion technology it was felt opportune to hold a meeting in this area. Furthermore the use of energetic atomic and ion fluxes is also becoming of increasing importance in assisting or modifying the growth of thin films in a number of important industrial processes and it was therefore rational to combine the, study of both erosional and growth processes in a single meeting. These proceedings include 16 invited review and 15 oral or poster presented contributions to the NATO Advanced Study Institute on the "Erosion and Growth of Solids Stimulated by Atom and Ion Beams." The review contributions span the range from the fundamental concepts of ballistic sputtering, and how this influences surface morphology evolution, through processes involving entrapment of incident species to mechanisms involved in'the use of chemically reactive ion species. Further reviews outline the influence of energetic irradiation upon surface growth by atomic deposition whilst others discuss technologkal applications of both areas of growth and erosion."

The European Community's Indirect Action Research Programme on the Safety of Thermal Water Reactors had as main obj ectives to execute useful fundamental research, complementary and confirmatory to on-going work in national programmes, and to improve collaboration and exchange of inform ation between laboratories in the Member States. The Seminar was aimed to report on work performed during the last five years and to identify useful further research areas with a tentative assessment of the state of the art for future work in certain issues of LWR-safety. The results obtained in 33 research projects executed in different national laboratories of the European Community were presented, evaluated and discussed, together with a number of invited papers on topics related to the research programme. Topics covered mainly within 3 distinct research areas or sub-programmes: Research Area A: The loss of coolant accident (LOCA) and the func tioning and performance of the emergency core cooling system (ECCS). Fundamental work on thermalhydraulics and heat transfer during refill and reflood of an uncovered core after a LOCA. Research Area B: The protection of nuclear power plants against external gas cloud explosions. Study of the impact on plant structure and systems of external explosions of dense combustible gas clouds due to accidental releases of hydro carbons in the vicinity of the plant. Research Area C: The release and distribution of radioactive fission products in the atmosphere following a reactor accident.

P. de Bernardis, S. Masi , G. Moreno Dipartimento di Fisica, Universita' "La Sapienza" 00184 Roma Italy ABSTRACT. Anisotropy measurement techniques and results are reviewed, with special attention given to experimental problems. The cosmological relevance of the dipole anisotropy, the only anisotropy truly detected in the Cosmic Background Radiation, is discussed. 1. INTRODUCTION Anisotropy of the Cosmic Background Radiation at 2.7 K (CBR hereafter) is a cosmological topic with a wide range of applications. In order to define anisotropy let us consider fig. 1 a, where the celestial sphere is shown with two beams A and B, with beamwidth 0 and angular separation e. We define the anisotropy of CBR at angular scale e in terms of the difference i'2,1 between the CBR flux I(ex,u) measured in the two beams. At small angular scales (e ) a "stochastic" approach is preferred, and the anisotropy is defined as .cJ I = GBP (1) I e where the brackets indicate averages over the whole celestial sphere. At large angular scales e>l a deterministic approach is preferred, and the CBR flux I(ex, S) is expressed as a sum of spherical harmonics (2) I (ex, S) = I ~ aIm Y (ex, S) lm I,m The alm coefficients give the dipole, quadrupole and higher order components of the anisotropy. 257 P. Galeotti and D. N. Schramm (eds.), Gauge Theory and the Early Universe, 257-282.

Like a river, the progress of science has a tendency to run tast or slow. Once the water meets a dam, it may stop for a while, but eventually it will flow over the top and run fast again. In scientific research, a breakthrough to overcome a simile>r barrier is often made by a small number of scientists, or perhaps by a single person of special creativity, extraordinary talent and unusual perseverance. Through such individuals science can proceed in great strides. No one can deny that Professor Kazuo Takayanagi is one of these special individuals who have played a leading role in the field of atomic and molecular physics, as well as space physics. This book is dedicated to Professor Takayanagi on the occasion of his retirement from the Institute of Space and Astronautical Science. Professor Takayanagi was born in 1926 and grew up in Tomakomai in Hokkaido, the northern island of Japan. In his boyhood, he was interested in natural sciences, particularly astronomy. On 5th February, 1943, when he was attending secondary school, a solar eclipse was seen in his town. He organized a group of students from his school to observe the eclipse. He still remembers the scene: it grew so dark during the eclipse that two stars, Vega and Arcturus, could be seen. After graduation from the University of Tokyo in 1948, he entered the graduate school there.

Radiography with neutrons can yield important information not obtainable by more traditional methods. In contrast to X-rays as the major tool of visual non-destructive testing, neutrons can be attenuated by light materials like water, hydrocarbons, boron, penetrate through heavy materials like steel, lead, uranium, distinguish between different isotopes of certain elements, supply high quality radiographs of highly radioactive components. These advantages have led to multiple applications of neutron radiography since 1955, both for non-nuclear and nuclear problems of quality assurance. The required neutron beams originate from radioisotopic sources, accelerator targets, or research reactors. Energy "tailoring" which strongly influences the interaction with certain materials adds to the versatility of the method. Since about 1970 norms and standards have been introduced and reviewed both in Europe (Birmingham, September 1973) and the United States (Gaithersburg, February 1975). The first world conference on neutron radiography will take place in December 1981, in San Diego, U.S.A. . In Europe the interested laboratories inside the European Community have entered into systematic collaboration through the Neutron Radiography Working Group (NRWGl. since May 1979. This Handbook has been compiled as one of the common tasks undertaken by the Group. Its principal authors are J.C. Domanus (Ris0 National Laboratory). and R.S. Matfield (Joint Research Centre, Ispra) Major contributions have been received from R. Liesenborgs (SCK/CEN Mol) R. Barbalat (CEN Saclayl.

This book represents a compendium of the twenty most useful far-infrared (or submillimeter) lasers. In the case of each laser described here, we have been fortunate to have the author who is the pioneer and acknowledged authority describe the principles of operation and to prepare the list of emission lines. Until these lasers were developed during the past decade, the submillimeter range of the spectrum has been almost barren due to lack of sources of radiation. The lasers described here remain the only practical, powerful source of radiation between the wavelengths of one millimeter and ten micrometers. Many hundreds of emission lines have been listed here, some providing hundreds of kilowatts of peak power in pulsed operation, others providing many tens of milliwatts of continuous power. The hundreds of wavelengths of the emission lines are so closely spaced in the wavelength range between one millimeter and one-tenth millimeter that this source of radiation can be considered to be step-tunable. Of course, labora tory scientists still depend upon the black body source (mercury vapor lamp) and the Fourier transform spectrometer to provide con tinuous spectra, but for this we must deal with true energy starva tion at the sub-microwatt level. This critical review can be expected to serve as a handbook for decades in the future because it contains descriptions of fundamen tal principles and listings of fundamental physical data."