This volume contains the results of research and development connected with the creation oftelescopes intended for the new regions of the spectrum mastered by astronomy: the x-ray, submillimeter (far infrared), and radio regions. The creation of x-ray, submillimeter, and radio telescopes and the receiver apparatus connected with them is a complicated and, in many respects, unusual problem. Therefore, the experience accumulated at the Institute of Physics can prove useful to specialists working in this field, This volume is intended for scientists, engineers, and builders occupied in research and development in the fields of x-ray, submillimeter, and radio astronomy as well as for students of advanced courses in these specialties, V CONTENTS A Reflecting X-Ray Telescope for an Orbital Astrophysical Station. * * * * * * * * * 1 I. L, Beigman. L. A. Vainshtein, Yu. P. Voinov, D. A. Goganov, N. I. Komyak, S. L. Mandel'shtam, I. P, Tindo, N, A, Shatskii, and A. I. Shurygin Mirror Systems for X-Ray Telescopes. * * * * * * * * * * * * * * * * * * * * * * * * * * * * 13 I. L. Beigman, L, A. Vainshtein, Yu. P. Voinov, and V. P, Shevel'ko Extra-Atmospheric studies in the Submillimeter Range Using On-Board Telescopes . . * . . * * * * * . . . * . . . * . * . . . * . . * . * * . . . * * . . . * . . * * . 35 A. E. Salomonovich and A. s.

This collection contains survey articles dealing with the following topics: The Mach principle and its role in the general theory of relativity, the modern conception of the vacuum, new methods in the theory of Lie group representations, the coherent state method and its applica tion to physical problems, and the Newman-Penrose method and its application to problems in general relativity theory. v CONTENTS On the Problem of Singularity in the De Sitter Model . . . . . . . . . . . . . . . . . . . . . . . . . . 1 v. K. Mal'tsev and M. A. Markov On the Integral Formulation of the Mach Principle in a Conformally Flat Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 v. K. Mal'tsev and M. A. Markov Canonical Transformations and the Theory of Representations of Lie Groups . 25 A. N. Leznov, I. A. Malkin, and V. I. Man'ko The Newman-Penrose Method in the Theory of General Relativity. 73 V. P. Frolov vii ON THE PROBLEM OF SINGULARITY IN THE DE SITTER MODEL V. K. Mal'tsev and M. A. Markov The de Sitter solution in no way corresponds to the case of a world without matter, but corresponds rather to a world in which all matter is concentrated on the surface r = IT /2 which could proba bly be proved by taking the limit from a volume distri bution of matter to a surface distribution 1]."

This anthology is devoted to the theoretical and experimental study of coherent phenomena in quantum optics. Considerable attention is devoted to the investigation of cooperative effects in multilevel molecular and atomic systems. The theoretical analysis is based on a single approach, using the theory of groups, which makes it possible to present the results in a compact and physically elegant form. The results of a detailed experimental and theoretical investigation of the photon echo, self-induced transparency, and nutation are presented. The theory of a coherent resonant mechanism for the interaction of laser radiation with multi atomic molecules which causes "prompt" dissociation is presented. A number of applied pos sibilities, in particular, the control of radiation by laser light and laser isotope separation, are analyzed.

This volume examines a timely problem in solid state physics, the condensation of ex citons in semiconductors. The papers in this volume describe a new approach to the study of exciton condensation based on microwave-frequency conductivity and the breakdown of an ex citon gas in a microwave field, an effect discovered by the authors. These methods have been used in extensive studies of germanium and have produced important new data about the con densation process. In addition to the experimental data, a theory is presented for the micro wave breakdown of excitons in the presence of electron-hole droplets. Also included are three articles devoted to the experimental aspects of low-temperature semiconductor research. This volume will interest scientists and engineers involved* with research in solid state physics. CONTENTS Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 A. A. Manenkov Microwave Studies of Exciton Condensation in Ge. * * * * * * * * * * * * * * * * * * * * * * * * * 3 G. N. Mikhailova Microwave Breakdown of Excitons and the Kinetics of Free Carriers and Excitons in Germanium in the Presence of Electron-Hole Drops. * * * * * * * * * * * * 37 A. A. Manenkov, V. A. Milyaev, G. N. Mikhailova, V. A. Sanina, and A. S.

This volume, which comprises a collection of papers by leading Soviet researchers, is devoted to topics in the luminescence of semiconductors. An experimental check is made on a series of predictions of the theory of ionization domains. A new low-voltage luminescence of zinc sulfide is described and investigated and is found to be due to a high-frequency electrical instability. A detailed study of the electrical properties of the instability and of the characteristics of the emission testifies to the pre-breakdown character of the electroluminescence and to the acousto electrical nature of the instability. The luminescence excitation spectra of AIN crystals excited in the region of the fundamental absorption contain lines belonging to excitons and their phonon replicas. The symmetry of the electronic and vibrational transitions corresponding to parts of these lines is interpreted. The results of a study of the scattering of light by electron - hole drops in germanium are cited. The results are discussed on the basis of a theory of exciton condensation in which allowance is made for the diffusion of excitons toward the surface of the drops and for the surface tens ion of the electron - hole liquid. This volume will be of interest to a wide range of scientific workers, particularly those engaged in the study of luminescence and physics of semiconductors. v CONTENTS The Theory of Ionization Domains. Generalization and Experimental Check . . 1 M. V. Fok, E. V. Devyatykh, and E. Yu. L'vova Domain Luminescence of Z inc Sulfide . . . . ."

This volume contains the results of many years of investigations of pulse gas-discharge lasers carried out at the Optical Laboratory of the Lebedev Physics Institute in Moscow. The two papers report mainly experimental results obtained in studies of pulse lasers utilizing translations in metals (Isaev and Petrash) and electronic transitions in diatomic molecules (Kaslin and Petrash). Population inversion mechanisms and the principal properties of the lasers are considered. v CONTENTS Investigation of Pulse Gas-Discharge Lasers Utilizing Atomic Transitions A. A. Isaev and G. G. Petrash Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 l. Efficiency in a Gas-Discharge Laser. * . * * * . . . . . * * * . . * * . * . . * . * . * . 1 2. Review of the Literature * * * * * * * . * * * * * * . . * * . . . * * * * . * * * * . * . . . * 4 Chapter I. Kinetics of Output Power Saturation in a Three-Level System. * * * * * * * * 6 1. Level Populations and Saturated Power in a Three-Level System. * * * * * * * * 7 2. Absence of Decay of Laser Levels. * * * * * * . * * * * . * . * . * * * * * * * * * * * * * 8 3. Decay of Laser Levels by Emission of Spontaneous Radiation. * * * * .

This volume reports investigations which form part of a major series of theoretical and experimental studies being carried out in the Laboratory of Low-Temperature Plasma Optics at the Lebedev Physics Institute in Moscow. The papers give the results of systematic investigations of the chemical composition and of the electrical and optical properties of dis charge plasmas, and also of populations of laser levels. Reliable and detailed information is given on the dissociation of carbon dioxide gas in discharges; the nature of the velocity dis tribution function, average energies, and densities of electrons; and populations and vibrational temperatures of molecules in cw CO and CO lasers. 2 The material in this volume is intended for specialists in quantum electronics and low temperature plasma diagnostics. v CONTENTS Investigations of Physicochemical Properties of CO Laser Plasma 2 V. N. Ochkin Introduction . . . . . . 1 Chapter I Dissociation of CO Molecules in a CO Laser Gas-Discharge Plasma. . . 3 2 2 1. Brief Review of Investigations of Dissociation of CO in 2 Electrical Discharges. . . . . . . . 3 2. Method for Determining Gas Composition. . . . 6 3. Dissociation of CO in a Continuous-Flow Laser System. . . . ."

This anthology includes articles on experimental studies of the interaction of high-power electromag netic waves with collisionless plasmas and with electrons. The nonlinear interaction of waves with plasmas has been investigated both under free space conditions and in waveguides. A study of secondary-emission dis charges was made in order to ascertain their possible effect on measurements in waveguides. The results presented here on the interaction of high-power waves with plasmas and electrons are of interest to a wide range of physicists and engineers concerned with various questions on the interaction of electromagnetic radiation with plasmas, including microwave heating of plasmas and laser fusion. v CONTENTS An Experimental Investigation of Nonlinear Dissipation of Electromagnetic Waves in Inhomogeneous Collisionless Plasmas - G. M. Batanov and V. A. SHin........................... 1 Collisionless Absorption of Electromagnetic Waves in Plasmas and "Slow" Nonlinear Phenomena - V. 1. Barinov, 1. R. Gekker, V. A. Ivanov, and D. M. Karfidov. . . . . . . . . . . . . . . . . 25 . . . . Nonlinear Effects in the Propagation of Electron Plasma Waves in an Inhomogeneous Plasma Layer - V. A. SHin .............................. " .... .......... .. ........... ......... 53 A Study of Secondary-Emission Microwave Discharges with Large Electron Transit Angles - L. V. Grishin, A. A. Dorofeyuk, 1. A. Kossyi, G. S. Luk'yanchikov, and M. M. Savchenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .............. . . . . . . . . . . . . . . . . . . . . . 63 . . . ."

This collection of papers describes investigations of luminescence centers in II-VI crystal phosphors, ruby, and molecular crystals. These investigations were carried out using spec troscopy in a wide range of wavelengths, electron paramagnetic resonance, and polarization methods. The relationship between the thermal and optical depths of electron traps is con sidered specifically. The articles in this collection should be of interest to all scientists investigating the luminescence of solids. v CONTENTS Investigation of the Spectral-Luminescence Properties of Ruby as Active Laser Medium V. B. Neustruev Introduction . 1 Chapter I. Spectral Distribution of Luminescence Quantum Efficiency and Absorption Spectra . . " . . 5 Chapter II. Phosphorescence of Ruby. Energy Band Scheme. . . . 12 Chapter III. Color Centers in Ruby. . . 16 Chapter IV."

Nonlinear Optics Of Semiconductor Lasers.