Physics of Wave Phenomena最新文献

The maximum range of detection of an autonomous underwater vehicle (AUV) in the high-frequency region has been estimated range applying holographic processing. The estimation is performed based on numerical simulation of the sound field attenuation with distance and the experimental spectral characteristics of the underwater vehicle noise emission and the background noise of the water area.

The robustness of the holographic processing of hydroacoustic broadband signals with respect to the spatial and temporal inhomogeneities of the ocean medium has been experimentally studied. The experiment was performed in shallow water against the background of intense internal waves (IIWs). The sound source was a towed pneumatic emitter; a single hydrophone played the role of a receiver. The interference patterns and holograms of sound pressure for different instants, when a perturbation of the medium caused horizontal refraction or coupling of acoustic field modes, are presented. It is shown that, in the presence of IIWs (which perturb the source field), holographic processing makes it possible to separate the spectral densities of unperturbed and perturbed fields. This circumstance allows one to reconstruct the hologram and interference pattern of unperturbed source field, thus demonstrating the robustness of holographic processing of hydroacoustic signals in the presence of hydrodynamic perturbations.

The method of passive thermal compensation of the arrayed waveguide grating (AWG) demultiplexer based on a cut in the input planar waveguide and a controlled angle of rotation of a part of this waveguide is investigated. A possibility of performing this thermal compensation is shown, restrictions on the choice of the demultiplexer parameters to be observed for functioning of the demultiplexer are obtained, and relevant recommendations are given. A simple algebraic expression for the derivative of the compensation angle with respect to temperature is obtained, which is needed for development of the demultiplexer. In the given numerical example, this derivative is 3.5 × 10^–5 rad/K.

The design of resonant planar metal-insulator-metal (MIM) structures offers promising applications in the optical image processing field, especially for developing efficient and ultrafast systems for optical computing and edge detection. The present work extends approaches based on electromagnetic theory and coupled-mode theory to describe nature and characteristics of the resonances in absorptive interference structures. Obtained analytical expressions based on Fano representation relate the resonance properties of the interference structures with their geometrical and optical parameters. This approach was efficiently employed to describe optical properties of the MIM structures and optimize their geometrical parameters for applications in optical filtration and image processing. The review of recent developments for all-optical edge detection both in reflection and transmission highlights various challenges encountered.

We study analytically and numerically the possibility of implementing a simple mesoscopic demultiplexer based on bound states in the continuum (BICs), induced transparency, and Fano resonances. The demultiplexer is made of a Y-shaped waveguide with an input line and two output lines where each output line contains two stubs grafted on two different sites in a U-shape far from the input line. The BICs are obtained for specific values of the lengths of the stubs of U-shaped structures and the segment separating them. By detuning the two stubs slightly in an appropriate way, BIC transforms into Fano or electromagnetic induced transparency (EIT) resonances. We give closed-form expressions of the geometrical parameters that allow a selective transfer of the given state in the first waveguide without perturbing the second waveguide. The effect of temperature on the transmission resonances is also examined using Landauer–Buttiker formula.

It is known that swelling of Nafion polymer membrane in water is accompanied by unwinding of polymer fibers into the bulk of the surrounding liquid. This effect is controlled by the deuterium content in water. In this paper, we report the results of studying the adsorption dynamics of methylene blue (MB) dye on the Nafion surface for MS solutions based on natural water (deuterium content 157 ppm, unwinding effect occurs) and based on deuterium-depleted water (DDW; deuterium content 3 ppm, unwinding effect is absent). In addition, we investigated the water desorption dynamics upon drying a Nafion polymer membrane after soaking in an MB solution based on natural water and DDW. It turned out that the MB adsorption rate in MB solutions based on natural water is lower than in the DDW-based MB solutions. Finally, the water desorption upon drying was found to be accompanied by a change in the Nafion absorption spectrum. Specifically, upon water desorption, the low-frequency band of the doublet in the range from 600 to 800 nm in the absorption spectrum of Nafion with MB particles on its surface undergoes transformation with a shift to the short-wavelength region. This transition occurred earlier for Nafion soaked in a DDW-based MB solution. The found effects are related to the retardation of diffusion processes in the layer of polymer fibers unwound near the membrane surface. Thus, changing the deuterium content in the aqueous solution in which the polymer membrane is swollen by very small steps (from 3 to 157 ppm), one can control the dynamics of adsorption and desorption processes.

A shift of the frequency of resonances of stimulated low-frequency Raman scattering (SLFRS) of laser radiation in liquid suspensions of viruses with a change in the pump wave intensity has been found for the first time. It is shown that the experimentally observed dependence of the frequency of these resonances in a suspension of tobacco mosaic virus (TMV) on the pump intensity is explained in terms of the scattering mechanism proposed by us previously.

A simple analytical function of pressure versus specific volume and specific internal energy is proposed for describing thermodynamic properties of tantalum in the region of high pressures in the shock-compression and isentropic-expansion waves. On the basis of this equation of state, thermodynamic characteristics of tantalum are calculated in a wide range of degrees of compression and heating. The results of the calculations are compared to the available tantalum data of experiments with shock and centered simple waves. The above equation of state can be used to simulate adiabatic wave processes at high energy densities.

Aspherical microlenses and microlens arrays allow increasing efficiency of various optical devices. However, it is technologically challenging to produce these items. The problem arises from impossibility of making microlenses with an arbitrary profile in a characteristic size region of several tens of micrometers using traditional technologies like single-point diamond milling and thermal reflow. In this work, a precisely aligned combination of an aspherical microlens and a microlens array produced by the two-photon polymerization direct laser writing (2PP-DLW) is presented. This structure is designed and optimized using computer simulation methods. A unique photosensitive composition based on the methacrylate dye (derivative of benzylidene cyclopentanone) is used to produce the structures. A specific feature of the chosen composition is dependence of its mechanical and optical properties on the femtosecond radiation dose which could widely vary during the fabrication. The produced structures are investigated using laser scanning confocal microscopy, which allows reconstruction of the 3D image of the structures and detailed analysis of their morphological properties. The aspherical microlens aligned with the microlens array has a wide range of applications in production of complicated optical devices, optimized microobjective lenses for high-precision wave front sensing, and refractive X-ray lenses.