Table of contents

A novel technique for plasma synthesis of diamond films (and in future of other materials) with the aid of a stationary optical discharge in flowing mixtures of reactant gases was proposed and experimentally implemented. The use of a cw CO₂ laser of 2.5 kW power acting on an Xe — H₂ — CH₄ gaseous mixture, in an atmospheric-pressure reactor developed for the purpose, made it possible to achieve diamond film deposition rates of 30–50 μm h^-1 on an area of 1 cm². The characteristic features and advantages of this laser-plasma deposition technique are discussed.

Self-focusing of λ =1.06 μm radiation pulses of 30 ps duration in compressed hydrogen resulted in generation of an extended quasirotational anti-Stokes spectrum consisting of lines with a smooth spatial profile. An increase in the focal length of the lens, which focused the pump radiation in a cell, altered drastically the nature of the output radiation: a set of rings, corresponding to generation of a sequence of vibrational lines, was observed.

An analysis is made of the phase—photon-number uncertainty relation for multimode electromagnetic fields (wave packets). It is shown that the variance of fluctuations of the investigated quantities depends strongly on the relation between the pulse duration τ_p and the recording time T. If T ≪ τ_p , the uncertainty relation is similar to that applicable to a single mode, and the phase and photon number variances follow adiabatically the changes in the pulse envelope.

Radiation from a chemical oxygen — iodine laser was used for the first time to pump a Co : MgF₂ crystal laser. The attained differential (slope) efficiency of 40%, corresponding to a quantum efficiency of 62%, demonstrated that a Co : MgF₂ crystal can be used for efficient conversion and summation of iodine laser beams.

A design of a single-frequency semiconductor laser with the emission wavelength 1.06 μm is proposed. This laser is coupled efficiently to an optical fibre in the core of which a distributed Bragg mirror is formed. The radiation power at the fibre output was found to be 10 mW when the laser drive current was 65 mA. The line half-width was estimated to be less than 1 mHz.

A cw injection laser emitting near 808 nm was constructed and investigated. Reduction of the internal cavity losses and of the series resistance of the laser made it possible to increase the external differential quantum efficiency to 0.67 and to achieve a total ('wallplug') efficiency of 50% while keeping the heat sink at 10°C (the total efficiency was 45% at 45°C). Accelerated life tests carried out at elevated temperatures indicated that the operating life of the laser should be in excess of 10⁴h at 25°C.

The method of molecular beam epitaxy on a ZnSe substrate was used to grow a ZnCdSe/ZnSe structure with 115 quantum wells. This structure was made up into a cavity which included part of the substrate. Lasing was excited by longitudinal pumping with a scanning electron beam of E_e = 40 — 70 keV energy. At T = 80 K for E_e = 65 keV the threshold current density was 60 A cm^-2 and the output power was 0.15 W at the 465 nm wavelength. At T= 300 K the lasing (λ= 474 nm) occurred in the ZnSe substrate.

An investigation was made of the characteristics of KrF lamps with different types of excitation by surface and barrier discharges in which the dielectric material was sapphire. The conditions were determined for the attainment of an extremely high yield of the KrF* fluorescence with the internal efficiency η_in≈30 % and 22% for pulsed surface and barrier discharges, respectively. A homogeneous surface discharge was maintained without gas circulation when the pulse repetition rate was 5 × 10⁴ Hz. Quasicontinuous excitation of a surface discharge at near-atmospheric pressure made it possible to reach a KrF* fluorescence power density of about 80 W cm^-3, which was close to the limit set by the kinetics of the gaseous medium. Under prolonged excitation conditions the intensity of the UV output radiation was limited by the permissible heating of the gas to a temperature above which the operating life of the gaseous mixture containing fluorine fell steeply. This was the reason for the advantage of surface over barrier discharges: the former were characterised by a high thermal conductivity of a thin (~0.2 mm) plasma layer on the surface of the cooled dielectric, which made it possible to construct powerful highly efficient KrF and ArF lamps emitting UV radiation of up to 1 W cm^-2 intensity.

The nature and the degree of polarisation of optical radiation from a powerful industrial laser were determined experimentally by a method based on measurement of the absorption of the s and p radiation components with a polarimeter. Special attention was paid to selection of the optimal optical configuration of an unstable cavity for high-power lasers with circulating active media. One of such configurations involves the use of retroreflectors, such as a corner reflector or prism, which was investigated. Theoretical estimates were compared with experimental results.

The first detailed time-dependent kinetic model of a nuclear-pumped laser is developed for transitions in carbon and nitrogen atoms present in Ne—Ar— N₂—CO— H₂— O₂ mixtures. Numerical simulation is used to show that the main mechanism of pumping the upper active levels of carbon and nitrogen atoms in Ne—CO— N₂ mixtures is three-body recombination of atomic carbon and nitrogen ions. Dissociative recombination of an ArC⁺ ion becomes the main pumping channel when argon is added to a mixture. The optimal conditions and the ultimate laser output characteristics are identified. The calculated results are in satisfactory agreement with experimental data.

A study was made of the influence of an elevated temperature on the lasing efficiency of ytterbium—erbium phosphate glasses, including the influence of additional sensitisation with neodymium or chromium ions. Temperatures below 200°C had practically no influence on chromium-free glasses. In the case of glasses containing chromium the deterioration of the parameters with increase in temperature was the result of a fall of the quantum efficiency of energy transfer in the chromium—ytterbium pair and also of an increase in nonradiative losses associated with the presence of the divalent chromium impurity.

Targets with low degrees of compression, such as those with internal energy deposition, two-stage conical targets for lasers emitting pulses of duration of the order of 100 ns, and multilayer shell targets for short-pulse long-wavelength CO₂ and CO lasers may prove acceptable for hybrid thermonuclear reactors with high values (of the order of 10³) of the gain in the blanket. Estimates and one-dimensional calculations of the compression of such targets are reported for the laser radiation energy range 0.2–2 MJ.

A study was made of the dynamics of temporal and spatial changes in the spectral characteristics of plasmas. A three-stage mechanism of the damage to surfaces of alkali halide crystals by microsecond pulses from a TEA CO₂ laser was proposed: breakdown initiation (at a distance of 3–5 mm from the surface with a time delay up to 1 μs relative to the leading edge of a laser pulse), evaporation (after a further delay of 3–5 μs), and interaction of the adsorbates with a plasma jet and with the laser radiation, as well as heating and cracking of a crystal by the UV plasma radiation.

Laser oxidation of metals and alloys (steel, copper, brass, titanium, etc.) was investigated with a laser image amplifier based on a Cu laser making use of computer image processing. A method was developed for measuring the growth of an oxide film by recording the motion of interference minima (maxima) of the reflectivity for copper laser radiation when the oxide distribution was nonuniform. The results were compared with theoretical models.

An investigation was made of changes in the Raman spectra of germanosilicate optical fibres as a result of UV irradiation. The photoinduced changes in the spectra were of the same nature for all types of irradiation used. These changes increased with increase in the radiation dose and in the GeO₂ concentration in the fibre core and were evidence of a structural modification of glass.

Measurements were made of the wavelengths of the radiation generated in an optical parametric oscillator based on a KTiOPO₄ crystal. This was done for nonlinear elements with different cuts in the XY plane. The crystal was pumped with radiations from Nd³⁺:YAG and Nd³⁺:YA lasers. The temperature dependences of the output wavelengths were calculated and determined experimentally. There was a disagreement between the experimental and calculated angular and temperature tuning characteristics, which resulted from the influence of the absorption edge of the KTiOPO₄ crystal at the idler-wave tuning wavelengths 3.26–3.52 μm.

Nonlinear frequency conversion of neodymium laser (λ= 1.06 μm) radiation was observed when this radiation was injected into the core of a single-mode optical fibre made of nitrogen-doped silica. This resulted in generation of visible violet and near-ultraviolet radiation (355 — 430 nm). The conversion efficiency was up to 2 × 10^-4. The observed UV radiation was the result of the following processes: generation of the third harmonic of the fundamental pump frequency, stimulated Raman scattering of the third harmonic, and generation of the third harmonics of the Raman-scattered components of the pump radiation. Lasing was also observed in the 380–430 nm wavelength range at colour centres associated with the presence of nitrogen in the silica core.

An investigation is reported of nonlinear dynamics of a four-mirror Z-shaped cavity with mode locking by self-focusing. It is shown that the mode-locking region is nonuniform: it is characterised by the appearance of 'windows' of irregular behaviour of the system as the result of a change in the pump intensity or in the distance between the active element and a spherical mirror. Conclusions drawn from a theoretical analysis are confirmed by the results of a numerical experiment based on a fluctuation model.

Phase locking of the output radiation and mode selection were achieved experimentally in an external Talbot cavity, of length L=Z_T/4 and containing one linear array of eight wide-aperture laser diodes each 120 μm wide. Such phase locking was also attained for two parallel linear arrays. The radiation from a single linear array was characterised by the contrast parameter V=0.97 and by the angular width of the diffraction maxima amounting to 0.5 mrad at half-intensity corresponding to the diffraction limit for a linear array with a diode spacing period d=200 μm. A cavity with a tilted mirror was investigated and the feasibility of increasing the radiation intensity in the central lobes was demonstrated. Phase locking was attained experimentally for two linear arrays separated by a distance of 1600 μm. The angular width of the maxima was 0.5 mrad in the p—n junction plane and 0.25 mrad in a plane perpendicular to the junction.

The dependences of the lasing threshold, of the output power, of the spectrum, and of the polarisation azimuth of the radiation from a ring Nd:YAG chip laser on the azimuth of the linear polarisation of the pump radiation were observed experimentally for the first time. An attempt was made to account qualitatively for the dependence of the lasing threshold of this laser on the azimuth of the pump radiation polarisation.

Theoretical and experimental investigations were made of the influence of the detuning of the lasing frequency from the centre of the gain line on the modulation frequency ω_m in a type-1 self-modulation regime when the cavity is characterised by amplitude and frequency nonreciprocities. The moduli and phases of the coupling coefficients of counter propagating waves are arbitrary. It is shown that the amplitude nonreciprocity of the cavity has a strong influence on the nature of the dependence of ω_m on the frequency detuning. A comparison with the experimental results makes it possible to estimate the difference between the phases of the coupling coefficients of a ring Nd : YAG chip laser.

Active stabilisation of the self-modulation frequency in a monolithic ring Nd³⁺:YAG laser was achieved for the first time experimentally.

Dynamics of a solid-state ring laser with periodic pump modulation was investigated experimentally in the presence of a phase nonreciprocity of its cavity. New lasing regimes were discovered: periodic antiphase pulsed modulation of counterpropagating waves and synchronisation of chaotic intensities of counterpropagating waves, differing from the perfect synchronisation investigated earlier because the difference between the intensities of chaotic pulses travelling in opposite directions was a periodic function of time. The phase nonreciprocity reduced the range of existence of dynamic chaos in a ring solid-state laser.

An analysis is made of the optimal conditions for laser irradiation and of typical paths of man-made debris in laser-reactive protection of spacecraft. Protection is provided by the recoil momentum resulting from laser evaporation of the surface layers of a debris particle, which can change its path, thus avoiding an collision with a spacecraft. Estimates are obtained of changes in the paths of particles with a characteristic size 1 cm when they are irradiated by radiation from a laser located on the protected spacecraft moving along one of the circular orbits at altitudes of 200, 400, or 700 km above the Earth's surface.

A study was made of bimorph mirrors intended for industrial laser systems. The technical characteristics of cooled single-channel deformable mirrors were investigated in detail. Preliminary tests were made on uncooled bimorph mirrors in industrial laser systems based on a cw CO₂ laser with an output power in excess of 2 kW and on a pulsed copper vapour laser with an average power of 35 W.

An experimental comparison was made of the focusing of coherent quasi-Gaussian radiation beams from laser electron-beam tubes (quantoscopes) with the results of model calculations based on the Fresnel-Kirchhoff transformation of the complex amplitude of the transverse lasing-mode field. The resolving power of the projection systems based on electron-beam tubes was found to be 4–5 times higher than that attained in the usual projection kinescopes, and could reach 2000–3000 pixels per scanning line. It was also found that the optical resolving power of the projection instruments based on laser electron-beam tubes could exceed the resolving power of the same tubes calculated on the basis of the electron-optical parameters.