卷 24, 编号 4 (2016)

Acousto-optic Q-switched lasing has been obtained for the first time in a Tm:Ho:YbAGcrystal. The laser output power is analyzed as a function of the laser pulse repetition rate. It is found that at rates above 30 kHz the laser slope efficiency reaches maximum values (~20 to 30%), comparable with the efficiency in the cw mode. The shortest laser pulse width is about 40 ns, and the average output power reaches about 80mW.

Second harmonic generation (SHG) induced by an external pulsed-periodic electric field in a 5CB nematic liquid crystal (NLC) is investigated. Deformation of the NLC under this field is analyzed, and a possibility of its accumulation is established. The observed SHG features are due to the domains with quite different director orientations emerging in the NLC.

Raman spectrum characteristics of dried deoxyribonucleic acid (DNA) and two types of crystalline amino acids (L-lysine, D-asparagine) are compared in a wide range of frequencies, including the regions of lattice (7 to 200 cm⁻¹) and intramolecular (200 to 4000 cm⁻¹) vibrations. It is found that the spectral position of the low-frequency band in the Raman spectrum of DNA with a peak near 26 cm⁻¹ correlates with the Raman spectrum of high-Q low-frequency modes that manifest themselves in the crystalline amino acids under investigation. The low-frequency band of DNA refers to a twist-like vibrational mode of nucleobases. The intensities of this DNA mode and the high-Q lattice modes of the crystalline amino acids L-lysine and D-asparagine are several times as high as those of the Raman lines corresponding to the intramolecular modes. Resonant coupling of low-frequency modes of DNA and amino acid molecular chains is analyzed.

Probe-beam scattering spectra have been obtained for four-wave mixing of laser waves in the skin layer of intrinsic semiconductors. The spectra were recorded using the frequency dispersion of orthogonally polarized radiation, which arises as a result of nonlinear optical interaction with conduction-band electrons. The mixing of two counterpropagating light waves in a semiconductor, implemented under nonlinear excitation of longitudinal density oscillations in the plasma electron subsystem of the semiconductor, is theoretically considered. This mixing is shown to lead to the rotation of the probe-beam polarization vector. The results obtained are of interest, e.g., for studying optical metamaterials based on thin-film structures.

The possibility of generating longitudinal sound waves on a deformation potential in a semiconductor medium has been investigated. This generation is due to the excitation of internal longitudinal electric field in the plasma electron subsystem of semiconductor by external counterpropagating light beams.

The effect of a transverse dc electric field on two-wave mutual rectification in a graphene superlattice (GSL) is investigated. Two field orientations are considered: (i) the polarization plane is parallel to the GSL axis and (ii) the polarization plane is perpendicular to the GSL axis. In both cases, the constant field is perpendicular to the polarization plane. The current density is calculated within a one-miniband model using the Boltzmann equation in the approximation of constant relaxation time.

The microwave propagation in a 3D dielectric photonic crystal at the frequency range from 8.5 to 12GHz has been investigated. A frequency range where effective refractive index n_ef of the crystal approaches zero is found. In the frequency range where n_ef <0.2, themicrowave beam becomes collimated, sharpened, and free of diffraction noise. An excitation of a surface wave, propagating along the external surface of the structure, is revealed in same frequency range. This property of the photonic crystal structure can be used to screen and mask objects scanned by external radiation.

The dependence of the properties of a probe ultrabroadband electromagnetic pulse on the frequency dispersion of electrical characteristics of medium has been theoretically and experimentally investigated. The importance of taking into account the properties of the dynamic permittivity of a medium under study for interpreting experimental ultrabroadband deep ground penetrating radar data is demonstrated.

An experimental estimation of the sound source depth, based on measuring the amplitude ratio for neighboring wave field modes, has been performed on the Pacific shelf under the following conditions: path length about 10 km at a sea depth of about 53m; pneumatic source signal in the band of 200±10 Hz. The predictive parameters of the bottom have been reconstructed from the envelope of the signal received by a single detector. The noise immunity of the algorithm and its sensitivity to variations in the bottom parameters have been analyzed. The experimental results are found to be in good agreement with the theoretical predictions.

Analytical approximations are derived and a computer simulation is performed in order to study the regularities determining the decay of the components of vibration velocity vectors and low-frequency signal intensity with an increase in distance. It is established that the sound pressure and horizontal components of the vibration velocity and intensity decay similarly, whereas the vertical components decay more rapidly. It is shown that approximating dependences are determined to a great extent by the distance between the source and detectors and are in good agreement with the exact laws describing the decay of the regular field part.