Table of contents

Conic targets are shown to be a promising object for the investigation of cumulative effects, which allow the achievement of high energy densities, and their use in experiments involving highly concentrated energy fluxes can open up new possibilities for investigating the physical properties of matter at extremely high temperatures, pressures, and densities. We outline the main experimental and theoretical results obtained to date that are related to conic target investigations and discuss their several possible applications in the future.

The dynamics of nonlinear solitary waves is studied by using the model of nonlinear Schrödinger equation (NSE) with an external harmonic potential. The model allows one to analyse on the general basis a variety of nonlinear phenomena appearing both in a Bose—Einstein condensate in a magnetic trap, whose profile is described by a quadratic function of coordinates, and in nonlinear optics, physics of lasers, and biophysics. It is shown that exact solutions for a quantum-mechanical particle in a harmonic potential and solutions obtained within the framework of the adiabatic perturbation theory for bright solitons in a parabolic trap are completely identical. This fact not only proves once more that solitons behave like particles but also that they can preserve such properties in different traps for which the parabolic approximation is valid near potential energy minima. The conditions are found for formation of stable stationary states of antiphase solitons in a harmonic potential. The interaction dynamics of solitons in nonstationary potentials is studied and the possibility of the appearance of a soliton parametric resonance at which the amplitude of soliton oscillations in a trap exponentially increases with time is shown. It is shown that exact solutions of the problem found using the Miura transformation open up the possibility to control the dynamics of solitons. New effects are predicted, which are called the reversible and irreversible denaturation of solitons in a nonstationary harmonic potential.

Mode-beating spectra and their current and temperature dependences are studied in a semiconductor laser. In the mode-beating spectrum of InGaAs quantum well lasers, the anomalous splitting of the difference-frequency line into three components f⁰, f⁺ and f^- is observed. The splitting increases with increasing optical power above the threshold. The component f⁰ is less mobile and shifts to the red with increasing temperature. The component f⁺ shifts to the blue, whereas the weak f⁰ component shifts to the red. The difference f⁺-f⁰ amounts to 400 MHz, which is ∼5% of the value of f⁰ in a 5-mm long diode cavity. No anomalous splitting was observed in quantum dot lasers.

The spectral perturbation is considered in a semiconductor active medium in the vicinity of the frequency of a strong electromagnetic wave. The nonlinear interaction of waves via the dynamic interference grating, or nonlinear scattering by population waves leads to the shift of resonance frequencies, which is manifested, in particular, in a change of the mode-beating spectrum of the laser. The spectral profile of this perturbation depends on the amplitude—phase coupling factor α. For large α, the profile becomes symmetrical in detuning from the strong-mode frequency. A change in the group refractive index corresponding to the 'slowing' of light is also calculated.

It is shown experimentally that two lasing zones, displaced directly towards the entrance of the laser channel, are formed in gas-flow lasers pumped by the fission fragments of uranium nuclei. As the pump power is increased, these zones merge into a single zone that expands towards the exit section of the channel. The time dependence of the lasing power qualitatively repeats the shape of the exciting neutron pulse.

The kinetic model of processes occurring in the plasma of an electric-discharge 193-nm excimer ArF laser operating on mixtures of He and Ne buffer gases is developed. The influence of excitation and active medium parameters on the lasing energy and total efficiency of the electric-discharge excimer ArF laser is studied theoretically and experimentally. It is shown that a specific pump power of ∼4.5–5.0 MW cm^-3 is required for attaining the maximum lasing energy for the highest efficiency of an ArF laser operating on a He—Ar—F₂ mixture. For the first time, the pulse energy of 1.3 J at an efficiency of 2.0% is attained for an ArF laser with a specific pump power of 5.0 MW cm^-3 using mixtures with helium as a buffer gas.

An efficient repetitively pulsed (RP) HF laser pumped by a barrier electric discharge with a 10-cm discharge gap is developed. A specific output energy E/V=3 and 23 J L^-1 and a technical efficiency η equal to 3.4% and 26%, respectively, were obtained in the single-pulse regime for non-chain and chain processes. An average output power of 43 W (E/V∼10 J L^-1 and η=11.3%) was obtained in the RP mode of the laser with a pulse repetition rate of 10 Hz for a depleted fluorine—hydrogen mixture (20% F₂, 5% H₂). Numerical simulation of laser operation under the conditions corresponding to the RP regime for an active medium length of about 0.5 m showed that a specific output energy of 15 J L^-1 and a technical efficiency right up to 20% can be attained in a single pulse. A specific output energy ∼14 J L^-1 attained under such conditions in the single-pulse mode for an active medium length of 0.37 m is found to be in good agreement with the theoretical values.

The temperature dependence of the efficiency of a laser based on a Fe:ZnSe crystal grown from the vapour phase by the free-growth method is studied in the 85–255-K temperature range. As the temperature was increased, the slope efficiency of the laser with respect to absorbed energy decreased from 43% (at 85 K) down to 9% (at 255 K) and its emission spectrum shifted from 4.0 to 4.17 μm. Lasing was obtained in a Fe²⁺:ZnSe crystal cooled with a thermoelectric module down to ∼220 K. In this case, the slope efficiency of the laser with respect to absorbed energy was 30%. The output energy of the thermoelectrically cooled laser was 142 mJ for the slope efficiency with respect to the incident pump energy equal to 21%.

The conditions of known experiments on the trigger acceleration of the radiative decay of isomeric nuclear states are compared. It is shown that in the case of quasi-monochromatic inducing sources, the use of Mössbauer targets can increase the efficiency of the process by a few orders of magnitude. It is pointed out that the asymptotic behaviour of the current value of the absorption cross section requires the comparability of the exposure time with upper-level lifetime of the transition.

The effect of the conditions of discharge on the output radiation parameters and efficiency of an electric-discharge XeCl laser pumped by 20 ns pulses is studied experimentally. It is shown that the highest specific energy extraction ∼3.9 J L^-1 atm^-1 from the active medium is realised in a discharge formed by pronounced macroinhomogeneities. The maximum laser efficiency of 2.7% is attained for discharge current densities of 1.2–1.4 kA cm^-2.

Various oscillation regimes of an actively mode-locked semiconductor laser are studied experimentally. Two types of regimes are found in which the minimal spectral width (∼3.5 kHz) of intermode beats is achieved. The width of the optical spectrum of modes is studied as a function of their locking and the feedback coefficients. The maximum width of the spectrum is ∼3.7 THz.

Mechanisms of laser swelling of polymers are considered. A theoretical model for one of such mechanisms is constructed and investigated. This mechanism is based on the formation of a thermoelastic wave upon absorption of a laser pulse. Tensile stresses in this wave lead to elastic and plastic deformation of a polymer in the heated region and to the formation of convex structures (humps). The threshold energy density of a laser pulse required for the production of a residual hump under laser irradiation is obtained analytically. A formula for the height of this hump is also derived. The model explains the earlier experimental data from the literature on swelling of a PMMA film irradiated by UV pulses.

Experimental data on the formation of ordered microstructures produced upon ablation of metal targets in liquids irradiated by a copper vapour laser or a pulsed Nd:YAG laser are presented. The structures were obtained on brass, bronze, copper, and tungsten substrates immersed in distilled water or ethanol. As a result of multiple-pulse laser ablation by a scanning beam, ordered microcones with pointed vertexes are formed on the target surface. The structures are separated by deep narrow channels. The structure period was experimentally shown to increase linearly with diameter of the laser spot on the target surface.

Based on the interferometric technique, a setup is built for measuring the spectral dependence of chromatic dispersion in fibres with a microstructure cladding. The setup provides measurements in a broad spectral range from 670 to 1550 nm taking birefringence in the fibre into account. The results of measurements of dispersion in a standard fibre with this setup and a commercial device are in good agreement.

Transmission spectra and optical losses of hollow photonic-crystal fibres (PCFs) filled with liquid-phase materials are studied. For hollow PCFs with a cladding period of about 5 μm and a core diameter of about 50 μm, infiltration with water increases optical losses by approximately two orders of magnitude relative to the optical losses of the same PCF before infiltration.

New results are presented on the efficient generation of UV radiation by using nonlinear DKDP and BBO crystals and a two-pass copper vapour laser amplifier with the enhanced peak power. The average power (average optical efficiency) of laser radiation at the sum frequency (λ=0.271 μm) was 3.6 W (24%) for the BBO crystal and 2.1 W (14%) for the DKDP crystal. The maximum average second-harmonic power generated by using the BBO crystal was 3.4 W (44%) at 0.289 μm and 2.1 W (27%) at 0.255 μm.

Tunable far-UV laser radiation is generated in the 204.7–205.5-nm region in a 3.4-cm long LB4 crystal by using noncritical noncollinear sum frequency mixing of the Nd:YAG laser radiation and the second harmonic of a tunable dye laser. A large value of phase-matching angular acceptance of 0.50 mrad is measured at noncritical phase-matching, which is 1.8 times larger than the critically phase-matched value. A conversion efficiency of 2.1% is obtained for the generation of far-UV at 205 nm. Tunable UV radiation is also generated in the range from 246 to 255 nm using collinear second harmonic of tunable dye laser radiation in an LB4 crystal.

Lasing was obtained for the first time in an optical parametric oscillator (OPO) on an Hg_1-xCd_xGa₂S₄ crystal pumped by a nanosecond Nd:YAG laser. Due to the cadmium concentration gradient along the crystal axis, the OPO could be tuned under noncritical phase-matching conditions by a linear displacement of the crystal. The tuning range was 2.85–3.27 μm, with the maximum slope conversion efficiency equal to 6.6%.

The four-mirror cavity with a BBO crystal for frequency doubling in a wide-aperture argon laser is optimised. The dependences of the second-harmonic power on the displacement of a focusing mirror, the displacement of the crystal, and the discharge current are measured. These dependences are in good agreement with calculations. After optimisation, ∼1 W of UV laser radiation at 244 nm was obtained with the conversion efficiency twice as large as that for the known similar lasers. It is shown that the increase in the efficiency was achieved mainly due to the increase in the discharge-tube aperture.

The dynamics of formation of a nonlinear response of a double phase-conjugate (PC) BaTiO₃ mirror is calculated. It is shown that because of competition between processes of different types (related to the presence of several PC channels, the local and nonlocal components of the photorefractive nonlinearity), the transient and dynamic lasing regimes for this mirror can be substantially different. It is found that the development of lasing begins with the successive formation and phasing of dynamic holograms of two different types (two PC channels). It is shown that even under optimal conditions, the lasing regime is not stationary due to competition between processes of different types, and the parameters of output fields fluctuate in time in a nontrivial way (due to the presence of the in-phase and out-of-phase components). Several scenarios of transition to the dynamic chaos are described.

The modification of biological objects (polysaccharides and cells) by CO₂-laser radiation in water added drop by drop into the interaction region is studied theoretically and experimentally. Calculations are performed by using the models describing gas-dynamic and heterogeneous processes caused by absorption of laser radiation by water drops. It is found experimentally that the laser modification of polysaccharides leads to the formation of low-molecular derivatives with immunostimulating properties. A dose of the product of laser activation of the yeast culture Saccharamyces cerevisiae prevented the development of a toxic emphysema in mice and protected them against lethal grippe and also prevented a decrease of survival rate, increased the average life, and prevented the development of metabolic and immune disorders in mice exposed to sublethal gamma-radiation doses.

A new approach is developed for obtaining diffraction-quality incoherent images of objects observed through a distorting optical medium. In particular, a method is proposed for achieving the diffraction limit for resolving power, including the case of objects observed through a turbulent atmosphere, using comparatively cheap aberrational optical systems (including systems with composite apertures) without using any auxiliary adaptive devices. It is shown that the instrumental function of the atmosphere+telescope system can be reconstructed with the help of the radiation intensity distribution in an auxiliary plane, and then used for obtaining a diffraction-limited image of the observed remote object. Numerical simulation demonstrates the application of this method for identifying various objects by observing them through a turbulent atmosphere.