Table of contents

Topics associated with the fabrication and applications of holographic optical elements are reviewed. The existing optical elements do not always satisfy the requirements of coherent optics. The properties and applications of holographic zone plates, which act as hologram lenses, are considered. These hologram lenses can be used in holographic multiple imaging systems. Holographic diffraction gratings and some systems in which they are employed are described. Holographic elements used without additional optical parts, i.e., systems demonstrating most clearly the advantages of holographic elements, are discussed. Complex holographic systems performing functions outside the bounds of classical optics are considered.

An investigation was made of a neodymium-glass laser with an emission line < 5·10^–3 cm^–1 wide, operating under nonspiking free-oscillation conditions producing pulses of ~700 μsec duration. At threefold excess of the pumping over the threshold the output energy was ~30 J. The radiation emitted by this laser was used to control the radiation of a second neodymium-glass laser, which was Q-switched. The Q switching was performed by a rotating prism. When the second laser was injected with narrow-line radiation from the first laser, it produced giant pulses of 30 nsec duration and 0.4 J energy in the form of a line 7·10^–3 cm^–1 wide. In the absence of such injection the natural width of the emission line of the Q-switched laser was ~14 cm^–1.

A theory of the electromagnetic field is developed for elastically deformable media. This theory can describe changes in the mechanical, electrical, and magnetic parameters of a medium under the action of ponderomotive forces. A simultaneous analysis of the field equations in a medium and of the equations of motion of the medium makes it possible to introduce thermodynamic functions relating these parameters to each other. Expressions are obtained for the law of conservation of energy, thermal and electron equilibrium, equilibrium density, and density of the ponderomotive forces. Two examples of media consisting of isotropically or anisotropically polarizable molecules in a strong electromagnetic field are discussed in detail.

Design calculations are given for the thermal conditions in a YAG:Nd active element under continuous-wave (cw) conditions. It is shown that an allowance is necessary for the temperature dependences of the properties of the crystal at high pumping levels. Krypton arc lamps and vortex-stabilized discharges are compared from the point of view of the pumping efficiency. The results are given of an investigation of the dependence of the characteristics of the output radiation on the pumping power.

A metal film, exploded by the application of an electric current pulse, was used as a Q switch of a pulsed laser. The energy, time, and space characteristics of a laser with such a switch were investigated.

The results are given of numerical calculations of oscillation modes in unstable resonators. It is shown that slight smoothing of the mirror edges leads to a considerable improvement of the selective properties of a resonator. It is shown that, contrary to the predictions of the theory of unstable resonators with sharp-edged mirrors, oscillation in the lowest transverse mode described by the geometrical approximation is possible in real resonators with large equivalent Fresnel numbers.

The problem of stability of steady-state laser emission is considered for the case in which the resonator contains a medium whose refractive index is a function of the radiation intensity. It is shown that the instability threshold decreases as the diffraction losses increase. This threshold is derived for the cases when a nonlinear instantaneous-response dielectric or the active substance itself acts as the nonlinear medium.

It is shown that the laser action in a resonator with plane-parallel mirrors is of single-mode nature if the pumping level is high. Stable transverse oscillation modes are characterized by waves which are generated near one edge of the resonator and travel at right angles to the laser axis.

A theoretical investigation is made of a ring laser subjected to a longitudinal magnetic field in the case when the anisotropy of the resonator is purely circular in nature. Four-wave emission is considered. Two separate cases are discussed: 1) two pairs of identically polarized circular waves traveling in opposite directions; 2) two orthogonal pairs of circular waves. A nonlinear interaction between the traveling waves and the stability of both cases are considered.

A theory of the development of mode locking in a ring laser is given. Equations are obtained for the relationship between, the forward and reverse waves in the course of bleaching of a nonlinear filter. The equations are compared with the time characteristics of the forward and reverse waves in a ring laser determined experimentally with an image-converter camera. It is shown that the time characteristics of the forward and reverse waves are strongly correlated when the concentration of the bleachable absorber is high, but this correlation becomes weaker with decreasing concentration of the absorber.

A shock-tube investigation was made of a gasdynamic CO₂–H₂O–N₂ laser. The gas mixture escaped through a slit. A probing beam, produced by a separate electricdischarge CO₂ laser, was used to study the gasdynamic laser. The parameters of the gaseous mixture, heated by a reflected shock wave, were T₅ = 1300–2250°K and p₅=5–88 atm. The main task was to establish whether population inversion could be achieved in the case of high water content in the active mixture of the gasdynamic laser when the [H₂O] concentration was comparable with the [CO₂] concentration. Gain was observed right up to [H₂O]/ [CO₂] = 1 for a mixture with [N₂]/[CO₂]=4 at T₅=2250°K and p₅=22 atm. In this case the maximum gain was observed at a distance of 25 mm from the slit and it amounted to 0.4·10^–2 cm^–1.

An experimental investigation was made of the stability of the oscillation frequency of a mercury vapor laser emitting at λ = 1.53 μ. The stability was determined by measuring the difference between the frequencies of two independently stabilized lasers. A method was found for improving the reproducibility of the frequency of a stabilized mercury laser.

A theoretical analysis is given of the conditions for the reconstruction of plane images with the aid of a semiconductor laser. The requirements which have to be met in recording of holograms of transparencies with a gas laser are derived. The conditions are obtained for the case when the number of resolvable elements in the reconstructed image is governed by the diffraction limit.

The efficiency of liquid crystals as light switches is considered. An array consisting of a glass disk with'embedded electrodes, a liquid crystal, and a transparent electrode can be used to record holograms at a rate of 50 cycles per second without loss of high contrast in the image. Liquid crystals with a memory can be used in the preparation of data before input into an optical computer and for output from an electronic computer.

An investigation was made of the frequency characteristics of the switching on and off of the dynamic scattering of light in nematic liquid crystals in alternating electric fields. A study was made of the influence of an alternating electric field and of short field pulses on the duration of dynamic scattering. A complete image-recording cycle was less than 1.2 msec and it ended with complete relaxation of a liquid crystal to the transparent state.

Coherence can be investigated using not the process of recording, but the reconstruction of a hologram, which acts as a diffraction shearing interferometer. One such hologram can be used in studies of the coherence of different (including thermal) light sources. The coherence of a mercury lamp operating at very high pressures was investigated in this way.

A theoretical and experimental analysis is made of the signal/noise ratio of the scattering in optical matched filters. An allowance is made for the scattering noise of a signal transparency and a spatial filter. Analytic expressions are derived and used to determine the optimal dimensions of filter functions correspondingto maximum degree of multiplexing. An equation is given for estimating the information capacity of a filter. The results can be used to formulate the requirements which the scattering characteristics of the photographic materials must satisfy in order to achieve the desired information capacity of an optical filter.

A discussion is given of a vaporization of a metal by the action of a high-power electron beam formed as a result of pulsed vacuum breakdown. The optical parameters of such a beam (10⁸ W/cm² for electrons of 100–200 keV energy) make it possible to supply an energy sufficient for the sublimation of each atom. When an energy of 450 J is supplied from a storage capacitor to a vacuum diode, it is possible to attain a metal vapor concentration of at least 10¹⁷ cm^–3 in a volume of 20 cm³.

It is shown that the collective interaction of an ordered beam of particles with matter can give rise to coherent resonance effects (excitation, stimulated emission, ionization, etc.) if one of the eigenfrequencies of the beam, associated with its periodic structure, is equal to the frequency of a quantum transition in matter. The energy transferred to matter by one particle in the beam may be much less than the energy of this quantum transition.

A theoretical analysis is made of the possibility of stimulated emission of photons of energy differing considerably from the energy of a quantum transition. This analysis is performed for the specific case of a beam of population-inverted particles interacting with a low spatial harmonic of an electromagnetic field near the surface of a diffraction grating.

The geometrical-optics approach is used in an analysis of the influence of the inhomogeneity of population inversion, which appears under spiking conditions, on the transverse structure of the radiation field of a laser. It is shown that under certain conditions the inversion inhomogeneity at right angles to the resonator axis has little influence on the properties of the output radiation. The results are given of an experimental investigation of the transverse structure of the radiation emitted by a neodymium-glass laser under conditions corresponding to different degrees of influence of the inversion inhomogeneity.

An investigation was made of radiative recombination and of stimulated emission from Pb_1–xSn_xSe crystals (x=0.04, 0.05, and 0.07) grown by the Bridgman method and from Pb_1–xSn_xTe crystals (x=0.17 and 0.18) grown from the vapor phase. The emission wavelength at 90°K was in the 8–11 μ range. The pulse output power was 1–10 mW. The temperature dependences were investigated. The maximum working temperature was below 140°K.

An electron-beam-pumped cadmium sulfide laser was developed in the form of a sealed unit cooled with liquid nitrogen. The electron energy was up to 60 keV, the density of the electron-beam current up to 10 A/cm², and the laser radiation output up to 40 W. The duration of the output pulses could be varied from 10^–6 to 10^–10 sec by modulation and scanning the crystal with the electron beam. The pulse repetition frequency of the electron beam was up to 200 Hz and the scanning frequency of the beam was up to 1 GHz.

A description is given of a voice communication system which utilizes an uncooled GaAs injection laser. Stable communication is provided by the system over distances up to 6 km for atmospheric signal attenuation up to 2.5 dB/km. The principal characteristics of the epitaxial laser are given for temperatures from –40 to +40°C and pulse repetition frequencies up to 10 kHz. The peak output power of the laser is 5 W. No deterioration in the operating characteristics has been found after 100 h. The total weight of the system, including a stand and a power supply unit, is 15 kg.

An experimental investigation was made of the influence of heat treatment of p–n junctions on the characteristics of epitaxial and diffused GaAs laser diodes. The laser threshold decreased after heat treatment because of increase of the gain factor and the reduction by a factor of 5–10 of the threshold current density. The output power increased because the internal quantum efficiency became greater. The internal optical losses increased severalfold, indicating some deterioration of the waveguide properties.

It is shown that an effective method for selecting long-life injection lasers can be based on the initial rate of rise of the threshold current. This gives better results than the selection in accordance with the initial parameters. The aging mechanism is assumed to consist of the formation of new nonradiative recombination centers in the process of recombination of excess carriers.

The statistics of the failure of injection lasers was investigated experimentally in the pulsed mode at 300°K and it was compared with the Weibull distribution. A satisfactory agreement was obtained for a form parameter of 2. The influence of the repetition frequency on the average service life was investigated.

The results are given of an experimental investigation of the catastrophic and slow degradation of heterojunction lasers. It is shown that the catastrophic failure occurs when the average density of the optical energy flux is (2–4)·10⁶ W/cm² and the local density is 10⁷ W/cm². Depending on this density, the service life of heterojunction lasers can range from several minutes to 100 h or longer: The catastrophic failure can be regarded as the extreme case of the slow degradation under the action of radiation. Heterojunction lasers emitting pulses of ≥ 10 W power, 100 nsec duration, and 6 kHz repetition frequency can work for more than 100 h without suffering a large fall in the output power.

The construction is described and the principal characteristics are given of a sealed electron-beam-pumped GaAs laser with a "radiating mirror" resonator. The electron beam is deflected electrostatically. The pulsed output of the laser is 2 W, it emits at a wavelength of ~0.84 μ, and the diameter of the light spot on the target is 150–200 μ.

A thin metal film was used in the resonator for the selection of CO₂ laser rotational lines of wavelengths 9.6 and 10.6 μ. It is shown how this can be carried out in practice. A tentative explanation is given of some features of the typical emission spectra obtained when the resonator length is varied by λ/2.