Vol 27, No 3 (2019)

The behavior of water molecules at the density of 10¹³ to 10¹⁶ cm⁻³ in a fused silica tube at room temperature has been studied. The number of molecules in the gas phase initially injected in the tube is comparable to the number of molecules adsorbed on the walls of the pre-evacuated tube. The concentrations of molecules in the gas phase were measured by diode laser spectroscopy with an external optical cavity. An off-axis alignment of the cavity with a large set number of transverse modes was used, which made it possible to measure the concentrations of molecules with narrow absorption profiles, temporal resolution of 5 s, and the accuracy better than ±5%. A strong interaction of molecules with the walls was observed. The time behavior of molecules in the gas phase both after the injection of gas into the vacuum volume and after its rapid evacuation under dynamic equilibrium between capture and desorption processes is non-exponential. The characteristic time of these processes 10⁻¹¹ to 10² s depends on the redistribution of molecules between the gas and the near-wall layers, which is governed by the physical and chemical adsorption mechanisms. The theoretical results on the kinetics of the processes are in good agreement with the experimental data.

Excitation of coherent vibrations of different-sized polystyrene nanospheres at their acoustic eigenmodes in aqueous suspensions is observed in the laser pulse field. To substantiate the observed features, a model of interaction of an electromagnetic field with a dielectric in heterogenous media is developed which allows eigenmodes of nanospheres in a suspension to be calculated. The estimations are in satisfactory agreement with the experimental data.

Electron emission induced by surface plasmon polaritons (SPPs) or simply surface plasmons excited by high-intensity femtosecond laser irradiation of an ordered Au surface has been studied by time-of-flight (TOF) analysis of the emitted electrons. Significant differences have been found compared to the same analysis of smooth surfaces. The SPP field enhancement has been significantly increased in hot spots which have the same periodicity as the surface. In addition to the increased field enhancement, periodic narrow peaks have been detected in the TOF spectrum. In the laser intensity range, where the high-energy peak is present, some of (also periodic in time) less frequent narrow peaks are about twice as large as the remaining ones, indicating the detection of two electrons (Cooper pairs) at about the same time, namely within the resolution of the TOF spectrometer.

A planar graphene-based heterostructure is considered, which behaves differently: as a barrier or a quantum well at small or large momenta of charge carriers, respectively. This heterostructure contains a strip of gapped graphene with a lower Fermi velocity, surrounded by gapless graphene with a higher Fermi velocity. In this configuration, an interface state arises at the intersection point of dispersion curves. The transformation of this interface state into a fundamental bound state is investigated.

The characteristics of a laser based on Fe:Cr:ZnSe polycrystals, excited at room temperature by a non-chain HF laser (2.6 to 3.1 µm) have been investigated. High-temperature diffusion doping of zinc selenide (CVD ZnSe plates) with chromium and iron was applied. Two active elements were studied. In one of them, iron and chromium were introduced into the crystal through one of the ZnSe plate surface; i.e., the Cr²⁺ and Fe²⁺ concentration profiles were overlapped in the crystal. When fabricating the second element, iron and chromium were introduced from the opposite plate surfaces, and their concentration profiles were spaced. It is established that co-doping of zinc selenide with chromium and iron reduces significantly the slope efficiency and increases essentially the lasing threshold with respect to the absorbed energy in comparison with similar parameters of lasers based on Fe²⁺:ZnSe crystals, fabricated by the same technology. One of the main causes of the deterioration of lasing characteristics of the Fe:Cr:ZnSe laser in comparison with the Fe²⁺:ZnSe laser is the absorption of radiation at the lasing wavelengths in the range of 4 to 5 µm in chromium-containing crystals. The prospects of designing a laser with an active element operating at room temperature, in which iron ions should be excited due to the energy transfer from chromium ions, are discussed.

Results are presented that have been obtained in numerical and experimental investigations of three-layer single-mode and multimode polystyrene, liquid, and liquid-crystal integrated optical waveguides. Numerical simulation results are presented and compared to the experimental data. The form of the scatter diagram from both the coordinates of the observation points and the waveguide phase slow-down factor is investigated. Characteristic experimental scatter diagrams in the plane transverse to the plane of incidence are given for TE- and TM-polarization. Calculated and experimental scatter diagrams are found to be in satisfactory agreement. Measurement of optical loss in the waveguides has allowed determining, in particular, the root-mean-square roughness height of the substrates of the polystyrene and liquid waveguides, which fairly corresponds to the known surface finish. In the liquid-crystal waveguide, the investigations have been focused on the features of the TE- and TM-mode scattering in a wide range of the phase slow-down factor variation. Complicated nonlinear processes of radiation field transformation beyond the waveguide are observed experimentally and through numerical simulation. Statistical parameters obtained for the irregularities of the investigated waveguides are presented. In addition, the root-mean-square estimates are given for spatial fluctuations of the director and compared to the average correlation radius for fluctuations of local orientation of nematic liquid crystal molecules.

The power contrast of the laser pulse is measured by recording the pulse front profile with a large dynamic range at the Luch facility using a fast photochronograph and fiber-optic communication lines. The power contrast of the laser pulse is 10⁵. A way to increase the dynamic range of the method to 10¹¹ is shown.

A new direction-finding algorithm has been proposed based on the interferometric localization of a noise sound source. It implies the use of a single vector-scalar receiver, which makes it possible to determine unambiguously the direction. The results of a numerical experiment are presented.

The coupling efficiency of the slow-wave propagation mode along the cochlea was investigated by evaluating the overlap integral of the acoustic field on two adjacent cross-sectional planes. The dispersion diagrams of the fast- and slow-wave modes and the structural dependence of the angular wavenumber and coupling efficiency of the slow-wave mode were studied.