Table of contents

New nonlinear properties of orthorhombic Gd₂(MoO₄)₃ crystals were discovered. At 300 K it was possible to achieve efficient (~30%) extracavity second-harmonic generation by pumping with high-power nanosecond and picosecond laser pulses at λ = 1.064 μm.

An experimental method was developed for two-dimensional mapping of the relative populations of excited states of atoms and ions in a low-temperature plasma formed by optical breakdown. The method was based on coherent four-wave mixing with a resonance of the hyper-Raman type. An investigation was made of the spatial distribution of excited atoms and ions in a plasma generated by laser radiation incident on the surface of a metal target. The sensitivity of the method was enhanced by polarisation control of the profile of resonances in the spectrum of four-wave mixing.

A new sensitised scheme for optical pumping of praseodymium amplifiers, operating in the spectral range 1.3 μm, was proposed and investigated. The amplifiers were pumped in the absorption band of neodymium ions. In fluoride glasses with a high ytterbium ion concentration, the excitation energy was efficiently nonradiatively transferred along the Nd³⁺—Yb³⁺—Pr³⁺ chain.

A new medium for praseodymium fibre optical amplifiers is proposed: it is barium—indium—gallium—thorium fluoride glass sensitised with erbium and ytterbium.

The lifetime of high-power (430–460 mW, λ =0.98 μm) heterolasers was investigated at T = 70^oC. Slow degradation as well as sudden failure, characterised by a lognormal distribution, were observed. A statistical calculation was made of the maximum lifetime of heterolasers: it was found to be 5430 h at 70^oC for a pump current of 1 A.

Theoretical and experimental investigations were made of the power, spectral, and polarisation characteristics of superluminescent diodes based on (GaAl)As heterostructures with separate confinement and a quantum-well active layer. The technical characteristics of these diodes were not inferior to those of superluminescent diodes based on traditional double-sided heterostructures. The new diodes were superior to the traditional heterostructures in respect of the half-width of the emission spectrum which was up to 100 nm, corresponding to a coherence length less than 7 μm. Test samples of light-emitting modules based on the investigated diodes were constructed.

An investigation was made of the output characteristics of a chemical hydrogen fluoride laser with an active volume of 45 litres. This laser operated at a pulse repetition frequency of 1 Hz and it was initiated by two counterpropagating electron beams with large cross sections. A study was made of the dependence of the laser output energy on the density of the hydrogen fluoride mixture and on the oxygen impurity content. The maximum laser pulse energy was ~6 kJ. An nstable telescopic cavity ensured a radiation divergence of ~10^-4 rad at the expense of a slight reduction in the output energy.

A pulse-periodic Nd:YAG oscillator—amplifier system with compensation of wavefront distortions was assembled. The success of the compensation was deduced from the efficiency of second-harmonic generation in a KDP crystal. Right up to the pulse repetition frequency of 50 Hz the system retained near-diffraction divergence of the output radiation.

An investigation was made of the following dynamic operational regimes of three-section laser diodes based on (GaAl)As heterostructures with different connection configurations and different control signals: direct modulation of the current in the superluminescence regime and lasing under uniform injection conditions; self-modulation of the intensity (including hysteretic self-modulation bistability and chaotic spiking) and synchronisation of such modulation by a harmonic current signal; generation of picosecond optical pulses under the conditions of Q switching and mode locking in an external cavity; tuning of the emission wavelength. The investigated lasers were constructed to ensure good contact with single-mode fibre waveguides.

An investigation was made of the possibility of conversion of high-power laser beams into hollow Bessel beams with the first maximum in the radial field distribution in the form of a ring and a slight variation of the field in the direction of propagation. An analysis was made of the influence of real conditions during formation of such beams on their parameters. The limits were found on the divergence of the intial laser radiation and on the characteristics of one of the conversion components (phase screw). These limits had to be kept for the formation of the field distribution in the form of a hollow tube. Experiments were carried out with the aid of a beam former consisting of an axicon and a phase screw, and also with the aid of kinoform elements equivalent to a combination of an axicon and a phase screw. The results confirmed the validity of the theoretical analysis. Hollow beams were formed with radial distributions described by the Bessel functions of the first, second, and fifth orders. The beam length was 20 cm and the diameters of the principal maxima were 20-60 μm.

It was found that, unless measures were taken to ensure single-mode emission, the dynamics of atmospheric-pressure CO₂ lasers resulted in mode-locking. This occurred primarily because of the high rate of the VV and RR exchange processes and because of the much higher (compared with nonpulsing radiation) gain due to the dependence of the gain-saturation radiation intensity on the degree of overlap of the fields of counterpropagating waves in the active medium of the laser.

An experimental x-ray spectroscopic investigation was made of the stabilisation of a Z pinch with a composite load in the GAEL (225 kA, 50 ns) accelerator. Kinetic calculations of the intensities of the L lines in the spectrum of copper were used for the first time to determine the parameters of a plasma [N_e ≈ (1–2)×10²⁰ cm^-3, T_e ≈ 300 keV] formed by injection of a cylindrical aluminium-plasma jet imploding onto an axial copper wire. Quantitative and qualitative analyses were made of the stabilisation of the Z pinch with a composite load. Spectroscopic methods were used to demonstrate the stabilising influence of the plasma jet. The results indicated that it should be possible to construct a homogeneous high-temperature plasma column.

An experimental investigation was made of the satellite structure of a resonance line of He-like ions in a plasma heated by λ = 10.6 μm radiation form a high-power pulsed electron-beam-controlled CO₂ laser. A method was developed for objective comparison of the experimental and theoretical distributions, on the wavelength scale, of the intensities of satellites of resonance lines of multiply charged ions with the aid of the least-squares estimates. This method was used as the basis of a practical determination of the electron density in a high-temperature laser plasma.

Strong 1.06 μm radiation was shown to be capable of orientationally selective bleaching of the F₂⁻ colour centres in a crystal of LiF. Conditions were found under which only identically oriented F₂⁻ colour centres remained unbleached. Crystals in which the F₂⁻ centres remained identically oriented were used to find the polarisation characteristics of two-photon absorption. The rate of bleaching of the colour centres as a result of two-photon absorption by an excited state was proportional to cos²θ where θ is the angle between the orientation of the electric vector of the strong wave and the axis joining the fluorine vacancies in the F₂⁻ centres. The two-photon absorption cross section of the excited F₂⁻ centres was estimated to be σ₂ = 3.5×10^-51 s cm⁴.

Nonlinear optical generation of the third harmonic in the vapour of a metal at a frequency close to the tripled frequency of an iodine laser was achieved for the first time. Phase-matching conditions in the presence of a buffer gas and the nonlinear susceptibility were close to the calculated predictions. A change in the energy of the third harmonic pulses with time was observed in a cell with cooled windows and a mechanism explaining this effect was proposed. The effect could be eliminated in an all-heated cell with better operational characteristics.

An effective numerical method for the solution of problems modelling the dynamics of a nonlinear interaction of a photorefractive crystal is developed and tested. The criterion of strongest suppression of dynamic phase distortions is used to optimise a system with two-beam energy exchange in InP:Fe.

An analysis is made of the conditions of focusing of non-Gaussian beams by an ideal thin lens which transfers light from a laser projection tube (quantoscope) to a large screen. It is shown that, under certain conditions, the resolving power of an image on a distant screen can be several times higher than the electron-optical resolving power of such tubes.

A general solution of the problem of the interaction between unidirectional distributively coupled waves with orthogonal polarisations is found an analysed. Interesting features of optical self-switching of these waves are identified and key formulas describing such switching are derived. It is shown that signal amplification as a result of self-switching may be extremely high and this can happen even when the coupling coefficient is zero. This case of zero coefficient is paradoxically of the greatest practical interest. The results obtained should be useful in working with birefringent waveguides and crystals.

A theoretical investigation is made of the characteristic features of acousto-optical nonreciprocal effects in anisotropic Bragg diffraction by travelling ultrasonic waves. It is shown that wide-aperture nonreciprocal acousto-optical devices can be constructed from wide-aperture acousto-optical modulators. The conditions are established for complete elimination of the amplitude and phase nonreciprocities of acousto-optical devices in the case of double anisotropic diffraction of counterpropagating optical waves.

An equation is derived for the transverse deflection of a beam of rays in the presence of a perpendicular component of the gradient of the Poynting vector amplitude. This equation can also describe one of the possible mechanisms of a transverse displacement of the focal waist when one-half of a focusing lens is illuminated by a plane circularly polarised wave. The transverse deflection is governed by the sign of the circular polarisation.

The spectra of two-photon-excited luminescence were determined for genetic structures containing aromatic and heterocyclic rings. A method was developed for increasing the intensity of the luminescence emitted by DNA and nucleohistone by introducing an activator. The presence of an activator in DNA nucleotide and in nucleohistone desoxyribonucleoprotein created conditions favourable for population inversion by two-photon laser pumping, which resulted in superfluo-rescence.

An investigation was made of the characteristics of hologram recording in films of photopolymerisable material Omni Dex^® 352. The kinetics of the diffraction efficiency during hologram formation in a film of this material was determined. The dependence of the hologram diffraction efficiency on the thermochemical fixing temperature, exposure power, and changes in the angle between the reference and object beams were studied. Omni Dex^® 352 can be used both in graphic arts and as a permanent optical data-storage medium.

An experimental investigation was made of the 'modan', a computer-generated holographic optical element which reconstructs the images of several modes. The modan was a matched spatial filter with angular separation of the channels. The results of measurements agreed with the theory and confirmed the expected performance of the modan. A comparison of two measurement methods led to recommendations on their use.

An analysis is made of the results of diagnostics of the active medium of a waveguide CO₂ laser by the laser spectrograph method. It is shown that a simplified approach to this method has led to errors in determination of the translational and vibrational temperatures of CO₂ molecules and, consequently, to an incorrect understanding of the physical processes occurring in the active medium of the laser.