Table of contents

An investigation was made of the energy parameters of a SF₆–H₂ radiation-chemical laser operating at pressures up to 10 atm. The active mixture was initiated by an electron beam formed in a field-emission coaxial diode. The maximum energy of the laser radiation obtained from a SF₆:H₂ = 70:1 mixture at a pressure of 2.7 atm was 0.79 J, which corresponded to a specific energy output of 21 mJ/cm³. The efficiency of conversion of the electron beam energy into laser radiation was 5%.

The reported results were obtained as part of an investigation of lead-tin chalcogenide lasers with spatial confinement. Stimulated emission was obtained from double heterostructures in which the active PbSnTe layer was grown by liquid epitaxy and the heterojunction was formed by vapor epitaxy of PbTe.

The Hill method is used in an analysis of the Schrodinger equation for a quatum system subjected to a time-periodic nonmonochromatic field. An algebraic equation is obtained and its degree in respect of exp(iET), where E is the quasienergy and T is the period of the external field, is equal to the number of levels. The coefficients of this equation are expanded in powers of the intensity parameter into a series with a factorial convergence even when one of the field frequencies is in exact resonance with one of the transitions. The Fourier components of the density matrix are expressed in terms of quasienergy considered as a function of the parameters of the problem and this gives approximate expressions outside the perturbation theory framework. Various results are obtained for a two-level system and, in particular, a formula is derived for the description of the natural lifetime of a quasienergy state.

It is shown that the gain of the Stokes radiation in stimulated Raman scattering by polaritons can be increased by reflection from the side surfaces in a layer of a nonlinear crystal whose thickness is close to the pump beam diameter but is much greater than the transverse shift of the Stokes waves parallel to the crystal length. The steady-state energy characteristics are considered (for strong and weak polariton damping) in a system with feedback in respect of one of the waves excited in the layer. It is shown that when the resonator Q factor is sufficiently high, the major part of the pump radiation energy is converted into the resonant Stokes wave.

The optical strength of BaF₂, NaCl, and CaF₂ crystals as well as of KI and KU quartz glasses was measured at the wavelength of 1.06 μ. The investigated crystals and KI glass were found to have high concentrations of absorbing inclusions in the bulk. A study was made of the dependence of the surface optical strength on the size of the illuminated spot in the range of relatively large spots (up to 1 cm in diameter). The surface strength of BaF₂, NaCl, and CaF₂ crystals was considerably less than the strength of quartz glasses and of K-8 glass. The surface damage was explained by a probabilistic model of local damage at absorbing inclusions.

An experimental study was made of the spontaneous parametric noise limiting the maximum sensitivity of near-infrared detectors with a preliminary frequency up-conversion. The angular distribution, polarization, and spectral characteristics of this parametric noise were found to be identical with the corresponding characteristics of the converted radiation, and the noise power was a near-quadratic function of the pump power.

Efficient stimulated emission from a new organic dye 2-phenyl-5(4-difluoromethylsulphonylphenyl)oxazole was obtained in the violet range when this dye was excited with nitrogen laser radiation (λ=337.1 nm).

An experimental investigation was made of the influence of buffer gases on the threshold excitation power and duration of stimulated emission from a POPOP vapor laser. The high threshold power was attributed to the absorption by excited singlet molecules in the stimulated wavelength range. An estimate was obtained of the singlet-singlet absorption cross section and the rate of accumulation of triplet molecules.

The application of inhomogeneous longitudinal ac magnetic fields to the active medium of an iodine photodissociation laser made it possible to control effectively the duration of the output pulses.

Single-frequency stimulated emission was obtained from a selective resonator of a nitrogen laser. Injection of an external single-frequency signal into a laser operating in the superradiance regime destroyed the stochastic structure of the spectrum and resulted in the emission at the external-signal frequency.

An investigation was made of the characteristics of the pulse copper-vapor laser operated under self-heating conditions. Various gas-discharge tubes were used and the discharge conditions were varied over a wide range. An output power of 6–16 W and efficiency of 0.4–1% were obtained for small-bore tubes.

An analysis was made of the dynamics of population inversion and photon field density in an amplifying medium enclosed in a totally reflecting cavity and characterized by fast inversion switching. A dimensionless parameter D representing the stability of this medium is introduced. It is shown that the self-excitation delay in the D≫1 case results in retention of the initial stored energy density for a finite time governed by the specific gain, whereas in the D < 1 case the influence of self-excitation can be ignored.

A correlation was found between the threshold of internal damage to NaCl, KC1, and KRS-6 crystals by CO₂ laser pulses and the transmission of these crystals near the short-wavelength edge of the transparency region. This correlation could be used as a method for nondestructive determination of the optical strength of materials suitable for high-power infrared lasers.

An investigation was made of a pulse CO₂ laser with a nonself-sustaining discharge. When an unstable resonator was used, the energy per pulse was 7.5 kJ. Calculations were made of the dependences of the energy characteristics on the resonator coupling coefficient. The theoretical calculations were in good agreement with the experimental results.

An optical waveguide was prepared by the diffusion of Ti in LiNbO₃. Optical surface waves were diffracted by acoustic surface waves of 110 MHz frequency. Acoustic waves of ~100 mW power were used to pump to 95% of light from the zeroth maximum to the first (85%) and second (10%) maxima.

An analysis is made of the relative contributions of radiative and nonradiative dipole-dipole energy transfer from donors to acceptors during laser action in binary solutions of polyatomic molecules excited by nanosecond and picosecond pump pulses. A study is reported of systems with overlapping donor luminescence and acceptor absorption spectra, where both donor and acceptor are capable of stimulated emission. Spectral-polarization methods are used to show that the radiative energy transfer mechanism predominates in the investigated systems.

A determination was made of the temperatures in the focal region of a lens just before laser damage to homogeneous regions in the interior and on the surface of K-8 glass. The softening temperature was also determined. A preliminary heating of the surface to ~600°C reduced considerably the number of defects formed by the mechanical treatment of the surface. The threshold damage temperatures of the surface and interior of the glass corresponded to the onset of formation of bubbles of the gas dissolved in the glass.

It is shown that distortions appear in a signal propagated in a dielectric waveguide with a quadratic-law variation of the refractive index. These distortions are avoided if the refractive index varies in accordance with the hyperbolic cosine law.

Fundamentals of the theory of the optical parametric oscillators (OPO's) are reviewed and formulas are presented for the calculation of the main OPO parameters (Secs. 1–6). Experimental results obtained in the development and investigation of various types of OPO and their applications are discussed (Sec. 7). Methods for extending the tuning ranges of OPO's (Sec. 8) and the possibility of realization of four-photon oscillators (Sec. 9) are considered. The review concludes with a comparison of various types of tunable laser (Sec. 10).

Double ionization chambers were used in a study of 10–70 eV radiation emitted from a plasma focus in an erosion-type magnetoplasma compressor. The maxima corresponded to the recombination of electrons terminating at the ground state of singly, doubly, triply, and multiply charged ions. The plasma focus emitted 45% of its total energy in the 12–70 eV range and could therefore be used as an efficient source of far ultraviolet radiation in establishing a population inversion in a medium by photoionization of the inner-shell electrons.

An investigation was made of the temperature and concentration dependences of the lifetime and probability of nonradiative relaxation of the excited metastable state ⁴F_3/2 of Nd³⁺ in a La_1–xNd_xP₅O₁₄ crystal. This crystal exhibited an anomalously weak concentration quenching of the Nd³⁺ luminescence, which made it possible to use high activator concentrations and made NdP₅O₁₄, a promising crystal for the fabrication of miniature lasers of the type required in integrated optics and optical communication systems. The experimental results obtained are in good agreement with recent non-Soviet work on spectroscopic and luminescence properties of this crystal. An interpretation is given of two experimental observations not accounted for earlier: the concentration quenching of the luminescence is independent of temperature and the constant of nonradiative decay of the excited metastable state of Nd³⁺ is a linear function of the concentration. It is concluded that the concentration quenching of the luminescence begins under energy supermigration conditions and the supermigration mechanism should occur also in other systems with high Nd³⁺ concentrations. Conditions are formulated for a weak concentration quenching of the luminescence from the ⁴F_3/2 metastable state of Nd³⁺.

Measurements were made of the mechanical pressure exerted on solid targets due to optical breakdown of gases near their surfaces. A study was made of the dependence of the impulse on the geometric parameters of the breakdown plasma, dimensions of the illuminated spot and target, target shape, pressure and type of gas. The results were interpreted on the basis of the theory of point explosions.

A calculation is reported of the sensitivity of the intensity of λ = 0.63μ, radiation, emitted from a helium-neon laser excited by a dc discharge, to discharge current fluctuations. The influence of simultaneous emission of λ = 3.39μ. radiation (due to a coupled transition) on this sensitivity if found for a wide range of discharge currents and current-fluctuation frequencies. It is shown that fluctuations of the intensity of the λ = 0.63μ radiation, resulting from the corresponding fluctuations of the discharge current, can be reduced considerably not only at low (0–1 kHz) fluctuation frequencies but also at a "resonance'' frequency which amounts to a few tens of kilohertz. The results of these calculations are confirmed by experimental results obtained in the frequency range 0–100 kHz.

An investigation was made of the dependence of the surface optical strength of K-8 glass on the dimensions of the illuminated spot whose area was varied from 2 to 120 mm². A neodymium laser system emitting pulses of 200 J energy and 10^–7 sec duration was used. For a fixed pulse duration the optical strength of the surface was not a single-valued function of the threshold power (energy) density but was characterized by a damage probability which depended on the radiation intensity and the size of the illuminated spot. The optical strength of parts of the surface illuminated with a series of light pulses of subthreshold intensity was higher than the strength of other parts. The experimental results were accounted for by a probabilistic mechanism of the damage due to the presence of absorbing inclusions distributed at random on the glass surface.

A picosecond rhodamine 6GDN dye laser was constructed. It was excited longitudinally by a train of pulses of the second harmonic of the neodymium laser radiation and the pulses emitted by both lasers were fully synchronized. The divergence of the dye laser radiation was minimized by matching the optical lengths of the resonators. The dye laser was tuned, within the range 550–602 nm, by a diffraction grating with 1200 lines/mm. The efficiency of conversion of the second harmonic into the dye laser radiation was 7%. The time and spectral characteristics of the dye laser were investigated.

Calorimetric receivers were used in a study of the distribution of energy between vibrational-rotational transitions in the P branch of the HF molecule in the radiation emitted from a F₂–H₂–O₂–He laser. The time dependences of the output radiation were studied with photoresistors. The results obtained were used in an analysis of the elementary processes occurring during stimulated emission.

An analysis is made of the design of high-power laser systems comprising a master oscillator and a-series of amplifiers forming a pulse of the required shape. A method is developed for calculating the signal entering the amplifier series, which is necessary for obtaining the required pulse at the output. This method is applied to an 11-stage amplifying system with elements correcting the pulse shape. An original design of a system generating pulses of required shape and duration is described and the results of experimental tests carried out on this system are reported.

Laser screens for cathode-ray tubes were made of single-crystal ingots of cadmium sulfide, cadmium sulfide-selenide solid solutions, and zinc selenide emitting in the 0.45–0.64 μ range. The homogeneity and stability of the radiation emitted from these screens were studied. The service life of laser screens was found to be governed mainly by the stability of the reflection coatings.

A method is given for the calculation of the parameters of thermal gasdynamic lasers. The rate equations are solved using the condition for steady-state emission, which makes it possible to find analytic expressions for the width of the stimulated emission zone and laser radiation intensity. A study is made of the influence of the rate of relaxation of the deformation mode of CO₂ on the laser parameters.

An experimental investigation was made of the stimulated emission of three longitudinal λ=0.6328 μ. modes from an He–Ne laser. The ranges of stability of the various three-mode-locked regimes were determined as a function of the gas pressure and pumping rate. Wen the detuning of the emission frequencies relative to the center of the gain profile was varied, narrow regions of unlocking of the mode beats were observed within the locking ranges with the ϕ=π phase. The minimum width of such regions was less than 6 MHz. Nonlinear self-modulation with a frequency of secondary mode beats in the range 2–10 kHz was observed in these unlocking regions. The experimental results and the theory were compared by a numerical calculation of the ranges of existence and stability of symmetric and asymmetric three-mode emission.

A theoretical analysis is made of the correlation methods for the search and separation of a signal from the background of noise. The initial information in the form of a Fourier transform is imaged onto the sensitive surface of a detector. Information reaches a photoelectric detector with a large sensitive area and use is made of a transient reference wave such that each element of the detector area is acted upon by a reference wave of definite frequency. Spatial optical information is processed by matched filters placed in the reference wave channel. Spatial pattern of the output current from the detector can be used to extract a signal and find its position in the input plane.

Coefficients of strictional nonlinearity of an isotropic solid are calculated for external self-focusing using elasticity theory equations. The average corrections to the refractive index and the anisotropy induced in the solid are determined. It is shown that strictional self-focusing can be investigated by measuring depolarization of probing radiation.

Theoretical and experimental investigations were made of the dependence of the quality of a reconstructed image on the ratio of the scales of inhomogeneities of the object and glass-plate diffuser fields. It is shown that the ratio of the signal to the noise resulting from recording of many holograms in one element improves if the random structure of the reference wave field is of the small-scale type. The improvement is proportional to the ratio of the typical scales of inhomogeneities of the object and the reference wave fields.

A relatively simple analytic method is proposed for calculating the energy and time characteristics of highpressure CO₂ amplifiers. An analysis of the amplifier operation is based on the selection of a series of limiting regimes by establishing a hierarchy of relaxation processes involving molecules in the active medium. The results of calculations are in good agreement with the experimental data.

Quantum efficiency η was determined for the fluorescence emitted from six dye vapors. The rate constants of the quenching of the fluorescence of POPOP, PPF, and PT vapors by oxygen were determined. The addition of a buffer gas (SF₆) to POPOP vapor increased the efficiency η. The mechanism of quenching of the triplet POPOP molecules by the dye itself was analyzed.

Eight types of five-layer planar dielectric waveguides for the optical wavelength range are analyzed to show that the use of an additional (second) cladding makes it possible to construct single-mode waveguides of large transverse dimensions. Higher stray modes are strongly suppressed (filtered off) by deliberately induced heat or radiation losses. A negative waveguide dispersion partly compensates the positive dispersion of the waveguide material. Signal distortions are estimated for single-mode and multimode operation of these waveguides.

A study was made of the influence of the radiation wavelength, focusing conditions, and temperature of a sample on the laser damage to SiO₂, TiO₂, SiO_x, TiO_x, (x<2) films and to the surface of rutile crystals. Possible damage mechanisms were considered.

A description is given of a mechanism of the transient transformation of energies and phases of light beams in recording of dynamic holographic gratings in weakly absorbing media. Simultaneous solution of a nonlinear system of permittivity and Maxwell equations for the transient case gives the parameters of the transformation of light beams used in the recording of such holographic gratings. The calculated parameters of energy exchange are compared with the experimental data for thermal holographic gratings in a solution of cryptocyanine.