Table of contents

A new method is proposed for measuring the spatial distribution of the quadratic susceptibility of inhomogeneous nonlinear media. The method is based on the unique relation of the Fourier harmonics of this distribution with the shape of a signal-radiation line during parametric frequency conversion in a linear regime. The diagnostic possibilities of the method of spontaneous parametric scattering of light are analysed by simulating the spectra of nonlinear diffraction in layered structures with different profiles of variation in the quadratic susceptibility. The cases of step and smoothed variations in the susceptibility of periodically poled regular and irregular superlattices (structures formed by the layers of optically linear and nonlinear media) are considered and the effect of light absorption at an idler frequency is studied. The experimental spectra of periodically poled crystals are presented. Different methods for measuring the one-dimensional dependence of quadratic susceptibility on the coordinate in periodically poled structures and polydomain crystals are proposed.

It is pointed out that the use of long-lived nuclear isomers in modern quantum nucleonics is impeded by a large broadening of the gamma line of metastable nuclear states, which exceeds many times their natural radiative width. This broadening can be eliminated if atoms containing nuclei form a Bose — Einstein condensate.

Anti-Stokes fluorescence from the ³P₀ level of impurity ions was detected in Pr³⁺ : Y₂SiO₅, Pr³⁺ : Lu₂SiO₅, and Pr³⁺ : Gd₂SiO₅ crystals non-resonantly pumped by laser radiation with a certain power density. The integrated intensity of the anti-Stokes fluorescence depends nonlinearly on the pump power density. As the atomic concentration of impurity ions was increased from 0.3% to 0.6% and 1.8%, the anti-Stokes fluorescence intensity was saturated due to the concentration quenching of the ¹D₂ term of the impurity Pr³⁺ ions. The anti-Stokes fluorescence and quenching of the ¹D₂ term occur due to the cross relaxation of the electronic energy of excited terms of the Pr³⁺ ions.

Active mode locking is studied in a diode laser with a three-mirror resonator upon the microwave modulation of the pump current. The mode-locking region with the minimal width of the spectrum of intermode beats is found, when the microwave frequency is close to the intermode frequency of an external resonator. This region is shown to be located close to the threshold pump current.

It was experimentally determined that introducing small additions of HBr into the active elements of a CuBr laser is similar to the addition of hydrogen and significantly improves the output laser parameters. The effect of additions to small-volume active elements is most pronounced (up to a five-fold increase in output power) and is less pronounced in large-volume active elements (up to a twofold increase). A special-purpose HBr generator was elaborated, making it possible to promptly provide the requisite concentration of the active addition in a sealed-off active element.

The lasing regimes of a diode laser with an external mirror are studied using the Lang — Kobayashi (LK) equations in the limit of a small distance from the mirror. The system of LK equations is integrated directly with the help of a program package developed. In addition, the instability and bifurcation points of solutions are found by calculating numerically the contour integral and the spectrum of Lyapunov exponents is calculated. The hysteresis zones of the lasing dynamics are found, which appear when the phase of a reflected signal changes. The parameters are determined at which two or three attractors corresponding to different dynamic regimes coexist in the phase space. It is shown that, when the rest of parameters are fixed, an increase in the pump power leads to a chaotic regime according to a classical scenario via period-doubling bifurcations. The regions of parameters are found in which packets of regular pulsations are generated, and the transition of these packets to the chaotic regime is observed.

A loop phase-conjugation scheme based on an axially symmetric four-wave interaction of focused light beams is proposed. It is shown that, when a longitudinal dispersion is introduced into the light beams, this scheme allows a phase conjugation of spatially coherent broadband radiation. The region of coherent interaction of focused longitudinally dispersed light beams is estimated.

The optical and nonlinear optical properties of colloidal solutions of silver obtained by laser ablation in water and ethanol are studied. It is shown that freshly prepared colloids experience a full or partial sedimentation by changing their nonlinear optical properties. Aqueous colloids undergo a partial sedimentation and their nonlinear optical absorption changes to nonlinear optical transmission. The obtained results are interpreted using the Drude model for metal particles taking the particle size into account and can be explained by the sedimentation of larger silver particles accompanied by the formation of a stable colloid containing silver nanoparticles with a tentatively silver oxide shell. The characteristic size of particles forming such a stable colloid is determined and its optical nonlinearity is estimated.

The SRS conversion of high-repetition-rate trains of self-phase-conjugated giant pulses of a Nd:YAG laser is studied in a BaWO₄ crystal. The SRS radiation with the average power up to 7.5 W and the single-pulse energy in a train of 30 mJ was obtained at the SRS conversion efficiency of 20% — 30%. The optical power of a thermal lens produced in the BaWO₄ crystal pumped by the 30-W laser radiation was 0.12 m^-1, which is an order of magnitude lower than in the known Ba(NO₃)₂ crystal.

The results of numerical simulations are outlined for the evolution of a 0π pulse in a medium with an inhomogeneously broadened quantum transition neglecting irreversible relaxation. A rule is formulated for the prediction of the 0π-pulse structure at long distances, which relies on the notion of the 0π-pulse area as the area under the curve of the modulus of its envelope. Analytical relations between the duration, the peak value, and the propagation velocity are given for the 0π pulse of the breather type.

The ratio of the components of the third order nonlinear susceptibility tensors (which are responsible for the self-action effects) in KDP, DKDP and LiNbO₃ crystals is measured at the 1064-nm wavelength of a Nd:YAG laser. Measurements were made on the basis of analysis of polarisation dependences of the focused radiation transmission by the z-scan method. The obtained polarisation dependences of the effective Kerr nonlinearity correspond to a tensor of the fourth rank that is symmetric in all its indices. The measured values of the Kerr nonlinearities that are responsible for the self-action of o-polarised radiation were found to be (1.75 ± 0.55) × 10^-14 and (2.4 ± 0.8) × 10^-13 esu for KDP and LiNbO₃ crystals, respectively.

A new method is proposed for injecting hot ions into a magnetic trap, which is based on the Coulomb explosion of clusters ionised by radiation from a high-power femtosecond laser. The parameters of the trap required for the confinement of the hot plasma produced after the explosion of deuterium clusters are estimated. It is shown that the neutron yield in the d — d reaction in the trap can substantially exceed this yield directly in the laser beam focus.

A system is devised for optical heterodyning based on a femtosecond Cr:forsterite laser using a balance scheme for the laser noise compensation. The dependence of a heterodyne signal on the time delay is measured by detecting backscattered laser radiation from a strongly scattering porous object (a sheet of paper). It is found that the backscattered signal contains 'a long tail' with an exponential decay caused by multiple scattering. The exponent of the exponential is determined by the lifetime of photons in a scattering layer. The absorption and scattering coefficients for different types of paper are measured by the photon lifetime.

The signal sensitivity and detection capability of a recirculation fibre ring interferometer (RFRI) are studied experimentally upon pulsed pumping of an intracavity ytterbium-sensitised erbium-doped fibre amplifier (YEDFA). It is shown that the number of effective circulations of light in the ring resonator can be substantially increased in the transient regime above the self-excitation threshold when, however, lasing has yet no time to develop. It is found that the required transient regime is achieved due to the self-restriction (drop) of amplification in YEDFA caused by the saturation of the active medium with increasing radiation power in the resonator. The increase in the signal sensitivity of the RFRI and its detection capability by factors of 25 and 4, respectively, is demonstrated in the pulsed regime of the YEDFA.

New experimental results on direct measurements of the phase response of spherical liquid-crystal (LC) optically addressed lenses (OALs) are presented. A simple and easy-to-use formula for the focal length of an adaptive modal LC lens is obtained for the first time. The complex conductance is measured with an accuracy that is sufficient to find the aperture region contribution and the calculated conductance is in good qualitative agreement with the experiment. The possibility of using OALs for self-correction of defocusing and as adaptive laser-beam deflectors is proposed and demonstrated experimentally.

The density distribution in a pulsed xenon gas jet emanating through cylindrical and conic (supersonic) nozzles in vacuum was investigated experimentally and theoretically for different stagnation pressures and at different instants of time. The measurements were made from absorption of monochromatic soft X-rays (SXRs) (λ=13.6 nm) produced by a nanosecond laser-plasma source. Focusing normal-incidence multilayer mirrors were employed for the monochromatisation of soft X-rays and the production of transmission jet images (X-ray absorption patterns). Numerical simulations were made of the transient outflow of xenon in vacuum taking cluster production into account. The measured absolute density values and the density distribution agree nicely with the simulations.

Field configurations of two counterpropagating nonuniformly polarised Laguerre modes forming three-dimensional dipole traps for neutral atoms are proposed. Peculiarities of the stochastic dynamics of atoms in such traps, associated with the anisotropy of dipole forces and manifestations of various radiative friction mechanisms are analysed. The problem of increasing the confinement time for atoms in such field configurations is studied.