Table of contents

A method for the generation of high-order harmonics in two interfering waves is proposed. It is shown that phase matching is possible in such a method and its consequence is a considerable increase in the efficiency of conversion of radiation to a harmonic with a given number. The increase is particularly large when harmonics are generated in a low-density (subcritical) plasma. The conditions are found under which the increase is about four orders of magnitude. The use of two interfering beams makes it possible to separate angularly the generated harmonics without recourse to spectroscopic devices.

A new nonlinear Gd₂(MoO₄)₃ laser crystal was developed for generation of the second harmonic of 1 μm cw laser radiation. It is shown, that Nd³⁺:Gd₂(MoO₄)₃ is a promising material for cw crystal lasers with self-doubling of the emission frequency.

Picosecond and femtosecond pumping of a bulk nonlinear LaBGeO₅ crystal resulted in conical-ring generation of the second harmonic with Cherenkov-type phase matching. The 'Cherenkov rainbow' was observed for the first time.

An Ni-like x-ray laser scheme with a double-pulse laser driver is suggested for increasing the gain of the 3p⁶3d⁹4d →3p⁶3d⁹4p and new 3p⁵3d¹⁰4p →3p⁵3d¹⁰4s lasing transitions, and of a possible 'water-window' inner-shell 3d →3p (3p⁵3d¹⁰4p →3p⁶3d⁹4p) transition. The calculated gain coefficients for tantalum and tungsten are in agreement with the published experimental results for the 4d →4p transitions. Inner-shell lasing in a material with a relatively low Z, such as caesium, is suggested on the basis of this transition scheme. It is shown that the use of nonthermal electron pumping (by the second laser pulse) leads to higher gains.

Theoretical and experimental optimisation was made of the parameters of an Nd:YAG oscillator based on four-wave mixing (FWMF) with feedback. Use was made of a thermal-nonlinearity hologram and the energy efficiency under conditions of generation of giant pulses was determined. The efficiency reached was 60% when the energy pulse was 200 mJ for a 2-mm input beam of 50 mJ energy. The ability of the system to operate in the pulse-periodic (up to 25 Hz) conditions was demonstrated.

The basic layout of a cw electron-beam stabilised CO laser is described. The output power of this laser is up to 85 kW, the specific output energy is up to 100 J g^-1, and the efficiency is ~30%. The results are given of investigations of the operation of this laser for periods up to 5 s, including the energy characteristics of the discharge in gas mixtures, and the spectral composition as well as the divergence of the output radiation.

An experimental investigation was made of ways of increasing the specific energy characteristics of a self-contained supersonic cw chemical HF laser with a radial-expansion nozzle array 18 cm long. Optimisation of the chemical composition of the fuel (which was a F₂—D₂—He—H₂ mixture) improved the energy characteristics by 10–25% and made it possible to reach a specific output energy of 305 J g^-1. A 1.4-fold reduction in the size of the reactant mixing zone at the entry to the cavity increased the specific power by 50% and its maximum value was 180 W cm^-2. Possible further improvements in the specific energy characteristics are suggested.

Emission of 1.1–1.5 μm radiation from a superfluorescent laser with IR dyes in a polymer host was observed and investigated. The energy efficiency of conversion to the infrared radiation was ~3% for picosecond pumping with Nd:YAG laser radiation. Continuous tuning of the emission wavelength of the superfluorescent laser was possible in the 1.1–1.5 μm range by altering the dye concentration in the polymer. The optimal selection of compatible dyes and polymers intended as active media in picosecond IR lasers was considered.

An investigation was made of the emission of radiation by Xe—NF₃ and He—Xe—NF₃ mixtures pumped by a low-pressure glow discharge. The average output power of the 350 nm radiation was up to 20 W for a discharge tube 40 cm long with an inner diameter 9 mm. The efficiency calculated on the basis of the deposited energy was up to 6%. A qualitative analysis was made of the kinetic processes occurring under these conditions.

Experimental and theoretical investigations were made of an XeF laser pumped by a travelling ionising wave originating from a nuclear explosion. The results indicated that an efficiency, in terms of the input energy, could reach 1–3%.

A time-dependent self-consistent kinetic model is developed for a laser emitting as a result of the 3s →2p transition in the lithium-like nitrogen ion (λ = 26.5 nm) in an N₂—H₂ mixture excited by a hard-ionisation source. The results of a numerical simulation demonstrate that such a mixture can emit radiation in the superradiant regime. The optimal lasing conditions are identified and a study is reported of the influence of uncertainty in the plasma-chemical reaction constants.

The optical homogeneity of the active media of cw chemical lasers was investigated by interferometry. A study was made of how the optical quality of the active media was influenced by the characteristics of various configurations of nozzle arrays (classical nozzle—nozzle configuration, configurations with discrete supply of the secondary fuel to the supersonic channel, and those with radial expansion or with a honeycomb structure). The dependences of the integral optical homogeneity criterion, the Strehl number, on the main operational parameters of a laser were determined. The optical homogeneity of the active medium was reduced by intensification of the processes which improved the operational parameters.

An investigation was made of the active media of solid-state lasers based on Cr³⁺:Yb³⁺:Ln³⁺:YSGG crystals, where Ln³⁺ is Ho³⁺, Tm³⁺, or Er³⁺. The spectroscopic and lasing characteristics of these materials were determined.

A new method was developed for analysis of the operational effectiveness of a flexible mirror in an adaptive optical system. A cumulant criterion of the effectiveness against the background of the Poisson noise in the control channels of the system was used in this analysis.

The transmission and scattering coefficients of the cavity mirrors were determined at the wavelengths λ = 1.3–1.4 μm typical of the radiation emitted by an overtone cw chemical HF laser. The results obtained were used to formulate the requirements in respect of the quality of the optics (the reflection and scattering coefficients) and to propose optical cavity configurations for lasers with the active medium 40 and 70 cm long. These formulations and proposals were verified experimentally. The experimental small-signal gain was used in a numerical analysis of the influence of the mirror characteristics on the output power and the emission efficiency of overtone lasers of the investigated type. The optimal reflection coefficients of the output mirrors were determined.

A numerical investigation is reported of the characteristics of the stimulated photon echo (SPE) excited by a sequence of 2n (n ≥ 2) paired pulses in an extended medium. The evolution of these pulses during propagation is taken into account. The SPE is shown to have a threshold governed by the total initial area of the excitation pulses. Stable SPE amplification is observed when this total area exceeds the threshold value, which is π. The optimal conditions for the SPE are identical for optically thin and dense media. This is a cumulative effect. The existence of a threshold affects also the cumulative effect: the nature of the dependence of the SPE amplitude on the number of the excitation pulse pairs varies with their total initial area. The cumulative effect is observed also when the pulse areas are no longer small. The linear part of the dependence of the SPE signal on n becomes narrower when the dimensions of a sample are increased, which is a consequence of the nonlinear nature of the evolution of pulse pairs in extended media.

The problem of transmission of an ultrashort laser pulse by a thin semiconductor film in the exciton part of the spectrum is solved for low excitation levels. Analytic solutions of the equations describing the dynamics of the exciton—photon interaction are obtained for homogeneous thin films and for films with an inhomogeneously broadened exciton system.

An investigation was made of the optical damage to a GLS-type glass bombarded first with ⁶⁰Co γ rays. Irradiation of glasses of this type with ionising γ rays reduced their optical strength. This reduction was governed not only by the preliminary γ-ray dose, but also by the presence of certain impurities in a glass.

Semiempirical calculations were used to identify about 50 lines in the spectrum of a calcium laser plasma as the 3s3p³, 3s²3p3d—3p⁴, 3s3p²3d, 3s²3d² transitions in the silicon-like Ca⁶⁺ ion. The results obtained were the first step in an investigation of the transitions from highly excited configurations of the complex with n = 3 in an isoelectronic sequence of silicon-like ions.

It is shown that the coherence function of the radiation scattered by an object with a Lambert surface can be determined by a method of spatial convolution of the intensity field. The results obtained by this method are not affected by time instabilities of the radiation from a transmitter. A method is suggested for measuring the angular radius of a lidar object and an estimate is given of the potential precision of the method.

An analysis is made of a method for determining the time characteristics of radiation. This method is capable of recording the fine temporal structure that cannot be detected on the basis of the intrinsic temporal resolution of the recording apparatus. An estimate is given of the precision of the method which depends on the parameters of the method and on the accuracy of measurement of the quantities.

Bent channel waveguides, formed by the diffusion of K⁺ ions in glass, were used in a directional coupler with the efficiency of the transfer of power between the channels in the range 0.1–44%. The process of propagation of light in a directional coupler with two-mode bent channel waveguides, formed by K⁺-ion exchange, was investigated. The results show that such a coupler could be used as a mode selector.

An effective and simple intracavity laser spectroscopy method is proposed and investigated. This method is based on the feasibility of a considerable increase in the duration of lasing and of control of this duration within wide limits in systems with a longitudinal relaxation time considerably longer than the duration of pumping. The results of an experimental investigation show that the use of a Ti³⁺:Al₂O₃ laser can enhance additionally (by a factor of 10², which may be increased to ~10³) the sensitivity of this method, compared with extracavity absorption spectroscopy. The sensitivity control interval was 10^-4—10^-5 cm^-1. A distinguishing feature of the method is the use of a special algorithm for the processing of signals in order to eliminate the influence of strong fluctuations of the laser radiation energy (duration).

A study is reported of the influence of the frequency instability of a light source on a Fabry—Perot interferometer designed for measuring small displacements. A reduction in the interferometer base l reduces the dispersion, but only up to a certain limit corresponding to l ≈ (0.5–1)λ. For dielectric mirrors this limit is related to the intrinsic dispersion of the mirrors, which is independent of l and which corresponds approximately to l_mirr ≈ 0.3λ. Silver mirrors are characterised by l_mirr ≈ 0, but the useful working range begins from l ≥ 0.4λ. The cases of a metal mirror used in combination with a 'detuned' dielectric mirror and of resonant mirrors in a dispersion-free Fabry—Perot interferometer are discussed.

A theoretical and experimental investigation was made of the mechanism of formation of a lengthened train of pulses in a garnet laser. A comparison of the theoretical and experimental results indicated that the mechanism in question was associated with the absorption by free carriers when the laser cavity with hybrid mode locking contained a negative-feedback component in the form of GaAs.