Table of contents

The nonlinear dynamics of a class A four-frequency ring gas laser with elliptic nonorthogonal states of counterpropagating waves is studied based on a developed and experimentally tested model taking explicitly into account the dependence of the backscattering coefficient of counterpropagating waves on polarisation characteristics. It is shown that the instability of phase characteristics of the generated field cause the switching of the intensities, polarisation states, and phase differences of counterpropagating waves in the self-oscillation regime, the shift of the intensity switching over detuning caused by the phase shift of the wave due to nonzero ellipticity, the spontaneous phase symmetry breaking accompanied by the appearance of deterministic and noise-induced chaos, the multistability of attractors with different topologies, and symmetric and asymmetric chaotic, as well as stochastic oscillations.

The mode parameters of a rectangular cavity of a semiconductor laser emitting in the range from 850 to 880 nm are numerically calculated and analysed. Nearly quadratic microcavities with a side of length ∼10 μm are considered. It is shown that, unlike a Fabry–Perot cavity, a rectangular cavity has a much more dense system of nonequidistant modes, which in principle cannot be interpreted as modes of an 'efficient' Fabry–Perot cavity or a ring cavity. The maximum Q factor of modes in the cavities under study can exceed 10⁵, which corresponds to the reduced intracavity loss ∼3 cm^-1. The radiation field of the cavity can be interpreted as the field of four coherent sources located at the cavity corners.

The amplitude and duration of currents flowing in a discharge circuit of a laser are studied depending on the parameters of the active medium and excitation conditions. It is shown that a phantom current is determined by the specificity of charging the capacitive component of the impedance of a gas-discharge tube (GDT) in the laser. In this case, the current flowing through a thyratron is the charging current of the capacitive components of the impedance of the discharge circuit of the laser. As a result, currents flowing through the thyratron and GDT are substantially different. The active medium is at the same potential during the existence of the phantom current, which prevents prepulse electrons in the plasma from accumulating the energy required to realise inelastic collisions in the active medium.

Semiclassical equations describing the interaction of a probe pulse with a 'dressed' Bose—Einstein condensate of a rarefied atomic gas are proposed. The analytic solution of these equations is obtained for low-intensity pulses. The conditions of the appearance of a diffraction grating from recoil atoms are found. The existence of induced superradiance at the probe-beam frequency is predicted. The pulse propagation velocity in the condensate is determined as a function of its energy. The limits of the applicability of the two-level model of a 'dressed' atom are estimated.

The light-induced nonlinear response of SiO₂ synthetic opals filled with a dye solution in ethanol is experimentally studied. Excitation of samples by radiation with a power density of ∼10 W cm^-2 causes changes in their transmission and reflection due to the light-induced dynamic shift of the stop band of a photonic crystal. Synthetic opals studied in the paper can be used in optical gates and light-controlled switches.

The structure and motion of complexes of in-phase weakly coupled fundamental solitons in a wide-aperture class A laser with saturable absorption are analysed. The symmetry of the field distribution and its relation to the motion of the complex are studied. Due to the absence of wavefront dislocations in such complexes, the transverse radiation intensity and phase distributions are the symmetry objects, which simplifies analysis compared to the case when wavefront dislocations are present. Four types of the motion of soliton complexes are demonstrated: a motionless complex in the presence of two mirror symmetry axes; linear motion of the complex when only one mirror symmetry axis exists; rotation around a motionless centre of inertia in the absence of the mirror symmetry axis and in the presence of symmetry with respect to rotation through the angle 2π/M (M is an integer); and curvilinear (circular) motion of the centre of inertia and simultaneous rotation of the complex around the instantaneous position of the centre of inertia in the absence of symmetry elements.

The nonreciprocal effect is studied theoretically and experimentally by the example of collinear acousto-optic interaction in a birefringent crystal. It is shown that this effect at ultrasonic frequencies ∼1 GHz and above considerably influences the parameters of modern acousto-optic devices, in particular, tunable acousto-optic filters. The nonreciprocal effect is estimated for different acousto-optic materials.

A complex study of spicules of glass sponges Hyalonema sieboldi and Pheronema sp. is performed. It is shown that skeletal spicules represent a bundle of composite fibres cemented with silicon dioxide, which imparts a high mechanical strength to spicules. The presence of a layered organosilicon structure at the nanometre scale in the spicule cross section gives rise to a periodic spatial modulation of the permittivity of the spicule material, which allows one to treat spicules as one-dimensional photonic crystals. Upon excitation of basal spicules by second-harmonic pulses from a Nd:YAG laser, we observed a considerable increase in the fluorescence intensity in the long-wavelength region with a maximum at 770 nm, saturation and anomalously large fluorescence lifetimes.

The features of the correlation processing of a speckle pattern obtained after transmission of radiation from a single-fibre multimode interferometer (SMI) with few modes through a diffusion transparency are studied theoretically and experimentally. It is shown that this approach eliminates the influence of polarisation mode beats and of higher-order modes typical for the two-mode excitation of a SMI and allows the measurement of the elongation of a sensitive fibre piece by exciting few modes in a multimode interferometer.

A method is proposed to stabilise the frequency of a He—Ne laser with an intracavity nonlinear absorption cell by the calculated frequency of the 7→6 transition of F₂⁽²⁾P(7)ν₃ in methane. The long-term frequency stability and reproducibility are measured for a He—Ne/CH₄ laser with a telescopic cavity.

A new approach is considered which is used in holographic lateral shear interferometry and allows the combination of the displacement of a phase object under study during the recording of holographic interferograms with the optical processing of displaced and optically conjugate holographic interferograms. Depending on the method of optical processing of such a pair of holographic interferograms, several aberration-free interference patterns are observed, which reflect with different sensitivities variations in the light wave phase caused by the phase object. Due to the lateral shear, which is equal to or exceeds the linear size of the object, the interference patterns of the object are identical to interference patterns obtained in a two-beam, reference-wave interferometer. The possibility of using this method to control optical inhomogeneities in active crystals in solid-state lasers is studied experimentally.

The possibility of using the method of Talbot interferometry to control the wave fronts of wide-aperture pulsed HF(DF) lasers is studied experimentally. A search for sensitive screens for visualisation of radiation from a HF(DF) laser and other IR lasers is performed. Screens based on fine graphite powder on a rigid substrate proved to be most convenient for recording Talbot interferograms (talbotgrams). The emission of screens excited by laser pulses was detected with a digital photographic camera and images were processed in a PC. High-contrast talbotgrams of multifrequency radiation of a HF laser were obtained, demonstrating the possibility of controlling the wave fronts of HF(DF) lasers by the method of Talbot interferometry without separating an individual laser line.

An experimental method is developed for preparing nanostructures in the field of high-power laser radiation (∼10⁷ W cm^-2) upon deposition of vapours of carbon-containing materials on a cold substrate surface. A specific feature of the method is irradiation of a sample in air at room temperature and pressure close to 1 atm. The dependences of the morphologic properties of nanostructures on the distance between a substrate and a sample are determined. Variations in the size of deposited nanostructures and their characteristic shape depending on the chosen material are found.

The photophysical parameters of tryptophan molecules at a low concentration in aqueous solution are measured by the methods of nanosecond laser fluorimetry upon excitation by 266-nm laser pulses. Two-step processes (reversible and irreversible photochemical transformations) taking place in this case are described quantitatively and it is shown that they can be neglected at the exciting photon flux density F < 5×10²⁴ cm^-2 s^-1 in ∼10-ns pulses.

The effect of energy removal from the combustion zone of a motionless optical pulsating discharge in the horizontal direction along the axis of a repetitively pulsed laser beam producing the discharge is discovered. The directivity diagram of a hot gas flow is formed during the action of hundreds of pulses. The effect is observed for short pulse durations, when the discharge efficiently generates shock waves. For long pulse durations, the heated gas propagates upward, as in a thermal source.

The parameters of sealed off barrier excilamps are studied at high excitation powers. The total output pulse energy up to 25 mJ is achieved (the emitting area of a KrCl excilamp was up to 1500 cm², the output power was above 100 kW, and the efficiency achieved 10%). It is shown that a volume discharge was formed in the coaxial excilamp when the energy supplied to the working mixture was increased and the pulse repetition rate was increased up to 50 Hz. The peak radiation intensity on the excilamp surface achieved ∼100 W cm^-2. The optimal excitation energy of a barrier excilamp was found to be 0.1–0.2 mJ cm^-3. The excilamp efficiency rapidly decreases with further increasing the input energy.

A scenario of the experiment on the observation of the isothermal Bose condensation of cooled gas with increasing the concentration of atoms caused by the deceleration of a vertical atomic beam in the gravitational field resulting in a decrease in the phase transition critical temperature below the gas temperature is considered. Coherent phenomena accompanying the evolution of the Bose condensate during further beam deceleration are pointed out.