I. N. Zavestovskaya

Determination of the adaptive fiber-optic interferometer sensitivity

The method for experimental determination of the sensitivity and detection threshold of the interferometer phase is proposed. Based on the method the indicated parameters for an adaptive fiber-optic interferometer are estimated using the dynamic hologram formed in the photorefractive CdTe crystal.

Adaptive photodetectors based on charge gratings in the problems of frequency-modulated optical signal detection

Nonstationary photovoltage excitation by frequency-modulated light in an adaptive photodetector based on GaAs is studied. To observe the effect, the crystal is exposed to light beams with the relative frequency shift Δf(t). Linear frequency modulation Δf(t) = At is used in the experiments. As a result of such illumination, a pulsed electrical signal is induced in the crystal. The pulse appears at the deceleration of the interference pattern motion, and its duration is controlled by the frequency variation rate A and the time of the charge grating formation. The possibility of using the effect in the systems for measuring velocities and accelerations of moving objects is shown.

Phase function method in problems of acoustic wave scattering

A generalization of the phase function method known in quantum mechanics to the problems of acoustic wave scattering on continuous medium inhomogeneities is proposed. The idea of the use of this method in acoustics is based on the fact that the wave equation for the acoustic potential or pressure in an inhomogeneous medium is reduced to the Schrödinger equation with a variable scattered field potential by a special substitution.

Theoretical modeling of laser fragmentation of nanoparticles in liquid media

A physical model of metal nanoparticle fragmentation in liquid media upon exposure to femtosecond laser pulses is proposed by the example of gold nanoparticle fragmentation in water. The model is based on electrolyzing the metal nanoparticles heated by laser pulses and their fragmentation during development of the instability of charged liquid metal drops. The nanoparticle charge gained upon exposure to laser radiation in water is estimated and the nanoparticle fragmentation parameter is determined.

Laser Ablation of Metals by Low-Density Picosecond Pulses

Thresholds of laser ablation ofmetals for the picosecond range of laser pulse duration are determined. Within the two-temperature metal model, the space-time dependences of the electron and lattice temperature are obtained. It is shown that ablation parameters become dependent on the pulse duration at the pulse duration τp ≥ τie, where τie is the cooling time of the electron gas. For noble metals, such pulse durations are τp ≈ 3 − 10 ps.

Laser annealing of porous defects in metals

In present paper a self-consistent model of laser annealing of porous defects in metals is presented. In the proposed model, the defects represent empty isolated pores whose dimensions are much less than thickness of the metal coating. Reduction of porosity occurs due to pore collapse in the molten pool under surface tension forces. In this case the research showed that pore collapse dynamics depends considerably on the pressure in the molten material. From the equality of the negative pressure in the melt and the capillary pressure the applicability bound of the model is determined. It is the critical melting rate of porous material at which pore collapse is still possible.

Photoluminescence properties of silicon nanocrystals grown by nanosecond laser ablation of solid-state targets in an inert gas atmosphere

It was found that the photoluminescence intensity decay kinetics of nanocrystalline silicon layers formed by nanosecond laser ablation of crystalline silicon targets in a helium atmosphere exhibit a power-law behavior with an exponent from 0.9 to 1.5, depending on the temperature and luminescence photon energy in the range of 1.4–1.8 eV, which indicates photoexcited carrier recombination controlled by dissipative tunneling processes in silicon nanocrystal ensembles in a suboxide matrix.

Mobile adaptive holographic laser seismometer

A prototype of a mobile laser seismometer based on a multiturn fiber-optic sensitive element and an adaptive holographic interferometer is developed. The possibility of recording weak seismic waves propagating in the “land-sea” interface region by the laser seismometer is shown. The original multiturn design of the sensitive element of the seismometer provides a threshold sensitivity of 1.6 · 10−7 m/s2 to seismic acceleration. The long-term operation stability of the laser seismometer is provided due to adaptive properties of the interferometer constructed using a dynamic hologram formed in the photorefractive bismuth titanate crystal.

Mobile adaptive holographic laser hydrophone

A mobile adaptive holographic laser hydrophone based on a dynamic hologram formed in a photorefractive crystal is developed. The hydrophone sensitivity is to –163 dB (rel. 1V/μPa) or 8.6 · 10−3 rad/Pa in the frequency range of 1–15 kHz. Field tests of the hydrophone were performed in water area of a sea bay. The results confirm the efficiency of the use of measuring systems based on adaptive holographic interferometers to solve problems of recording weak signals (acoustic, hydroacoustic, and others) under non-laboratory conditions.

Structure and magnetic properties of layers formed by laser fusing of powders on nonmagnetic substrates

Studies of the structure and magnetic properties of layers formed on nonmagnetic substrates by laser powder fusing (LPF) showed that crystalline phases are separated from initial powders of bronze, inconel (IN 625), and PGSR-4with the transformation of nonmagnetic materials to soft ferromagnets. The fused bronze powder layer exhibits soft ferromagnetic properties with two types of magnetic domains with the Curie temperatures of 80 and 300 K and a coercivity to 90 Oe at 300 K; in layers based on In625 and PGSR-4, only one type of magnetic domains with the Curie temperatures of 260–270 K is formed, which provides soft ferromagnetic properties at 4 К and the paramagnetic transition at 300 K.