Optical Memory and Neural Networks最新文献

Determining the order of a vortex beam is an important task in optics. The effect of various types of aberrations on the intensity pattern of vortex beams is studied in this work using numerical simulation in order to visualize the topological charge. The most effective types of aberrations for determining the topological charge of a vortex beam are proposed. The possibility of using a multichannel diffractive element was studied in order to simplify and speed up the determination of the topological charge.

We theoretically and experimentally investigated the transformation processes of polarization singularities (C-points, L-lines, V-points and rings, as well as the Stokes vortices) in vector structured Laguerre–Gaussian (sLG) beams with varying their controllable phase parameters. It was shown that all the Stokes vortices simultaneously turn to zero only in V-points and rings, in other polarization singularities only a part of the Stokes vortices vanish. On the basis of our computer simulation, the process of the birth and annihilation of polarization singularities has been studied. In the experiment, we used the intensity moments technique for the first time to measure the spectrum of vector modes and their digital multiplexing of a simple vector sLG₁₂ beam. The amplitude and phase spectra were measured in each linear polarized component of the space-variant polarization field. Then scalar fields of the polarization components were formed, which was the digital demultiplexing of the vector sLG field. The combination of the vector modes made it possible to restore the vector sLG beam again, that is the digital multiplexing the vector field.

The propagation of vector mode of the second-order in microstructured and gradient waveguides was numerically investigated applying the RSoft FullWAVE package. It was shown that the investigated vector beams of the second-order are the vector modes of the proposed waveguides. In the obtained fundamental modes, there are regions in which the energy flux is directed opposite to the beam propagation direction (regions of the reverse energy flux).

This work is devoted to the study of the morphology and structure of 3C-SiC/Si films obtained by the high-temperature chemical vapor deposition (HT CVD) method. Epitaxial growth is achieved by transforming the crystal by coordinated substitution of atoms, in which the overall structure of bonds between atoms is not destroyed. At the first stage of the conversion, the first half of silicon atoms Si is successively replaced by carbon atoms C as a result of reaction of Si with gas CO, and an epitaxial layer of cubic silicon carbide SiC-3C is obtained. At the second stage, the remaining half of Si atoms is consistently replaced by C atoms due to the reaction of SiC with CF4 gas. Depending on the orientation of the silicon surface, the pressure of the reagent gas, the temperature and time of growth, carbon structures with various properties are obtained, from nanodiamonds to nanotubes and onion carbon. The key feature of this method is that the substrate orders the resulting structures using the initial chemical bonds between atoms in silicon. Photographs of the surface of the structures are presented, demonstrating the features of silicon carbide film growth at different levels of the substrate holder. Analysis of rotational X-ray diffraction patterns showed the presence of silicon carbide films of the 3-C polytype.

In this paper, two imaging systems are considered: in the focal plane and in defocus. In the focal plane, the correctness of a multichannel filter fitted with sixteen Zernike polynomials is investigated. The modelling of the focal plane system is carried out using the Fourier transform. The simulation results show the effect of the aberration coefficient on the detection accuracy. In the case of defocusing, its effect on the accuracy of aberration detection is investigated. The modelling of the defocusing system was carried out using the Fresnel transform. Detection was found to be possible at a small distance from the focus and a small aberration intensity ratio.

Optical properties of a resonant diffraction grating with a period varying in the periodicity direction are studied at oblique incidence of light. Using rigorous numerical simulations based on the Fourier modal method, it is shown that in the case of relatively compact varying-period gratings, the period change rate must be taken into account, and the local periodic approximation commonly used for the description of such structures becomes inapplicable. Coupled-mode equations with varying parameters are obtained for the case of oblique incidence and solved analytically in terms of the complementary error function. The predictions of the developed coupled-mode theory appear to be in good agreement with the rigorous numerical results.

In this research, we investigated tight focusing of vector beams with negative orders. It is theoretically proven that the lengthwise component of the spin angular momentum is equal zero near the focal area only for the first order of the incident beam. It was shown using numerical simulations and Debye integrals that local subwavelength regions with circular and elliptic polarization of opposite signs are formed in front of and behind the focal plane.

Laser radiation produces an effect that is mainly determined by the ability of the optical system to create a given energy distribution over the worked surface of the material. The variety of existing and developing optical systems indicates the importance of solving this problem. The use of computer optics elements for redistribution of laser intensity in the focal plane is also important. This largely determines the course of structure formation processes in processed materials. The features of synthesis of porous and oxide nanostructures by laser irradiation are considered. When frequency-modulated laser beam is used, the synergistic effect between the thermal effects of laser irradiation and the pulse-periodic laser-induced vibrations leads to a significant increase in the diffusion coefficient. This is caused by the non-stationary stress-strain state of the material to be treated.

The process of focusing circularly polarized laser beams by plane diffractive lenses using the Richards-Wolfe formula is considered. It is established that in the focal plane of a light field with circular polarization circles of different radii with the center on the optical axis are formed. In these circular regions polarization vectors are twisted in opposite directions. The appearance of “spin” separation depending on the radius can be explained by the phenomenon of radial spin Hall effect in the focal plane.

In this paper, we considered design of the complex metalens with high numerical aperture. It proposed to be manufactured in a thin film of silicon nitride. The element represents two slanted sectored metalenses, every sector of which is binary sub-wavelength gratings set. The diameter of the proposed lens is 14 µm. Numerical modelling by applying the finite difference time-domain method demonstrated that the proposed element was able to detect laser vortex beams with different topological charges –2 and –1. Moreover, it can operate over the whole visible range of light. The proposed metalens is able to discern beams with different wavelengths since they are focused in different focal planes. The change of wavelength in a 1 nm produces the shift of focal spot in about 4 nm. In the case of a Gaussian incident beam with left circular polarizing, this metalens simultaneously forms two vortex beams with topological charges one and two at the focal length of 6 μm.