Table of contents

An experimental investigation was made of the energy conversion efficiency and of the effects of stimulated Brillouin scattering and of optical breakdown, limiting the maximum energy density obtained from several phosphate and silicate neodymium glasses when the duration of the output pulses was 50–150 ns. The experimental results were used to develop a numerical model for calculation of the gain allowing for these processes. A design was developed for an amplifier with ultimate radiation characteristics.

An investigation was made of the possibility of lasing of Ho³⁺ ions in a Yb₃Sc₂Ga₃O₁₂:Cr³⁺:Ho³⁺ crystal in accordance with a cascade scheme ⁵I₆→⁵I₇→⁵I₈ using flashlamp pumping at room temperature. The lifetime of the ²F_5/2 level of the Yb³⁺ ion and of the ⁵I₆ and ⁵I₇ levels of the Ho³⁺ ion were determined. The efficiency of the Cr³⁺→Yb³⁺→Ho³⁺ energy transfer chain was 60%.

Theoretical and experimental investigations were made of an ILPN-216A semiconductor emitter operating at 1.3 μm. A feature of the design of this emitter was a laser diode with an external resonator as the active element. The calculations were in good agreement with the experimental values of the mode intensity in the cw and pulsed regimes. In the pulsed regime when the ILPN-216A emitter was pumped additionally by a continuous threshold current, a single-frequency radiation spectrum was obtained and the ratio of the emitted mode to the adjacent mode was at least 20 dB.

Theoretical models developed independently by groups in Russia and Italy were used to describe the operation of a 10-liter electric-discharge XeCl laser. The calculations gave similar results for an HCl pressure of 1.5 Torr, but diverged strongly at low (0.5 Torr) and high (4 Torr) HCl pressures. The reasons for this discrepancy were determined. It was found that homogeneous models cannot describe the experimental data satisfactorily.

A theoretical interpretation is given of the effects in a free-electron laser with a longitudinal magnetic field oriented the opposite to the electron beam.

A multimode laser with a dynamic system typical of intracavity laser spectroscopy is analyzed allowing for a mechanism that may possibly flatten the stimulated emission spectrum when stimulated Brillouin scattering (STBS) occurs in the active medium. A numerical analysis of the dynamics of such a laser is carried out in terms of kinetic equations. It is found that STBS in an active medium shifts the lasing spectrum with time in the direction of the red wavelengths. The time needed for the establishment of dips in the emission spectrum of a laser, corresponding to narrow-band absorption lines, decreases on increase in the nonlinearity, but the relative depth of the dips decreases. An effect similar to the condensation of the spectrum in the vicinity of an absorption line is predicted.

Lasing was achieved in solutions of coumarin 7 (coumarin 535) pumped by an He–Sr recombination laser (430.5 nm). Jet and cell versions of the dye laser were used. The average output power of the jet laser was 15 mW, whilst that of the cell laser was 30 mW. The tuning range was 499–557 nm and the conversion efficiency was ~ 5%. A distinguishing feature, compared with dye lasers pumped by a copper vapor laser, was that the duration of the lasing pulse was an order of magnitude greater ( ~ 0.2 μs).

Pulses having an energy of 1 J with an angular distribution width close to the diffraction limit were obtained at the exit of a four-pass amplifier operating at a repetition frequency of 20–25 Hz.

Theoretical and experimental investigations of double-pass single-stage amplifiers are reported. A two-level approximation is used to derive analytic expressions for the gain in two important cases, with and without (ultrashort pulses) complete temporal overlap of the pulses. It is shown that, for small input signals, a 20% improvement in the ultrashort pulse gain can be achieved.

A phenomenological theory is developed and experiments are reported on generation of a reflected second harmonic in degenerate semiconductors when an electric field is applied to the surface. An analysis is made of the case of bulk degeneracy and of the degeneracy of carriers in a surface layer when a space charge region appears after application of a static field. A relationship is established between the field dependence of the intensity of the reflected second harmonic and the state of the surface of a semiconductor, such as the thickness and dielectric properties of an oxide film, surface charge (density of the surface states), etc. Nonlinear electroreflection is considered as a new experimental method for the investigation of the surfaces of centrosymmetric semiconductors.

An investigation was made of a resonant optical parametric oscillator based on the resonant third-order nonlinearity in sodium vapor. Synchronous bichromatic pumping was provided by picosecond optical pulses of good spectral quality. Dependences of the main parameters of the output radiation of a four-photon optical parametric oscillator on the sodium concentration and on the optical resonator length were obtained.

Expressions appreciably simpler than those used in the literature were derived for approximate calculations of the directions of collinear phase matching under conditions of optical second harmonic generation in biaxial crystals. This simplification was made possible by the use of expressions for the refractive indices obtained from the optical indicatrix rather than those determined from an analysis of the surface of the Fresnel normals.

An investigation was made of the feasibility of achieving four-frequency emission from a solid-state ring laser when two modes of different polarizations were emitted in each direction. In this regime the accuracy of measurements of optical nonreciprocal effects was enhanced. It was shown theoretically that this four-frequency regime may be achieved in a solid-state ring laser with a nonplane-plane resonator by intracavity second harmonic generation in a nonlinear element with type II phase matching.

An experimental investigation was made of the distribution of the energies of pulses of forward (concurrent) and backward first Stokes components of stimulated Raman scattering (STRS), and of pump (exciting) radiation pulses, transmitted by a scattering medium. The study was carried out under linear, intermediate, and nonlinear scattering conditions. The dependences of the coefficients of variation and of the asymmetry of the distributions on the energy of the pump pulses were determined. The statistical properties of the energy of the backward STRS pulses differed in a number of respects from the forward STRS pulses, including a relatively high coefficient of variation in the former case. An interpretation of these differences was developed. It was found that STRS gave rise to fluctuations of the energy of the transmitted pump pulses and the statistical characteristics of these pulses were determined. The results obtained for forward STRS were in satisfactory agreement with the conclusions reached on the basis of a quantum theory.

An investigation is made of the evolution of quantum fluctuations of a fundamental soliton in the course of its propagation in a nonlinear fiber waveguide characterized by losses and compensated by amplification. Simple relationships are obtained for the amplitude and phase noise, quantum uncertainty of the position and momentum, and also fluctuations of the quadrature components of the radiation field. Numerical estimates are obtained. It is shown that loss-compensating amplification is unnecessary for efficient formation of squeezed states of a soliton.

A theoretical justification is given of the widely used method of stabilization of the output signal from a fiber-optic gyroscope with a broad-band radiation source by a Lyot depolarizer. Different variants of including a depolarizer in such a gyroscope are considered and the role of the dichroism and birefringence induced in the gyroscope system is discussed.

A new method of calculating the propagation constants and wave eigenfunctions of guided modes is proposed for axisymmetric translationally invariant fiber-optic waveguides with arbitrary refractive index profiles. The method is based on solving a parabolic scalar wave equation. A comparison is made between the numerical solution under steady-state conditions and the eigenfunctions of single-mode and multimode waveguides.

A theory of the second ray invariant is proposed using the theory of plane Frenet curves. Its existence requires that the coordinate dependence of the refractive index in the waveguide cross section should satisfy the regularity condition: curves of equal refractive index differ only by an amount which can be obtained using an isotropic scaling transformation. The theoretical conclusions are illustrated using the example of waveguides having the generalized refractive index distribution n ( r ) = n [ (x/ a) + (y/ b)^q].

A quantitative physical model of metal cutting by cw laser radiation in the absence of chemical reactions was developed. An experimental study was made of the flow of the processing gas using a geometrically similar model. The distributions of the pressure and velocity of the gas were determined at the cutting front. Simplified mathematical algorithms for the thermal problem were constructed and calculations were made of the maximum depth of the cut (kerf) and cutting speed as functions of the laser beam parameters. Possible nonsteady-state characteristics of the motion of the melt and of the cutting front were considered. A thermal mechanism was proposed for the formation of the regular rippling of the kerf, based on a balance between capillary forces and forces exerted on the melt by the gas stream in the vicinity of the upper edge of the cutting front. Simple formulas were obtained for calculating the depth and period of the ripples.

A method of improving the accuracy of measurements of the wavelengths of spectral lines of multiply charged ions was proposed and implemented experimentally. The method involved recording the emission spectra of a recombining laser plasma. Wavelengths of various lines of F VIII and F IX ions were measured with a relative error Δλ / λ ≈ (6–8) × 10⁻⁵.

It was demonstrated experimentally that long-lived plasma bubble could form when a metal target in a gas was irradiated by a nanosecond ultraviolet laser pulse. Two interpretations of the observed effect were proposed.

An MF-14 photodiode array was used to determine the radiation field of pulsed ultraviolet lasers. The responsivity of this array at the wavelength of 0.337 μm was S = 4 × 10⁸ V/J. The distributions of the radiation from an N₂ laser were determined in the near-field zone. The distributions were also obtained for XeF, XeCl, and KrF excimer lasers in the far-field zone. The angular dimensions of the distributions were determined.

It was demonstrated that holographic gratings could be formed by temporally nonoverlapping optical beams. Effects involving coherent erasure by an individual pulse must be small to achieve efficient grating formation.

A calculation is made of the threshold sensitivity of a laser-interferometric antenna with a phase-conjugating resonator. The use of such a resonator for compensation of technical fluctuations of the signal laser is limited by the stability of the frequency of the reference waves pumping a nonlinear mirror. Recommendations relating to engineering design of an antenna with parallel arms are given.

The possibility is considered of correcting wavefront phase distortions in a nonlinear adaptive regenerative power amplifier system with a substantial reduction in the optical loading on the corrector. The experimental results obtained are compared with theoretical calculations.

A method is described for determining the reflection coefficients of high-density mirrors, based on the use of a mode-locked laser and a sensitive detector with a fast time resolution. The laser light is transmitted through an optical resonator formed by the investigated mirrors. The measured delay in the decay of a light pulse gives the damping time of the optical resonator. This is related to its Q factor determined by the reflection coefficients of its mirrors.