In this paper, several methods of forming a spiral intensity distribution are mentioned and it is noted that they mainly form a spiral in the far diffraction zone. To form a spiral intensity distribution in the near zone, the authors propose to illuminate a helical diffractive microaxicon. The results of numerical simulation within the limits of strict electromagnetic theory visually confirm that a spiral structure is formed. In this case, the formation is more qualitative and more reliable compared to the illumination of the binary spiral axicon.
In this study, we propose investigate of pulses in a waveguide with a three-dimensional diffraction grating with a subwavelength period. We varied the diffraction grating period. The diffraction patterns of vortex fields formed in the near zone of a diffraction grating in optical fiber were obtained numerically using the finite difference time domain (FDTD) method.
The comparative modeling of focusing of femtosecond Gaussian and Poissonian pulses was presented in this paper. Poissonian spectral shape pulses, as opposed to the Gaussian-shaped ones, allow to avoid negative frequency components. The spectral properties of pulses for various durations are investigated. Calculations showed that a significant difference between the Gauss and Poisson pulses begins only for very short durations (less than 3 fs). A comparative simulation of the focusing of short pulses, as well as the passage of focused pulses through a binary phase plate, is performed. The calculation was carried out on the basis of solutions of the Maxwell equations by the method of finite differences in the time domain.
In this work, the modeling of the propagation of the pulsed focused Gaussian beam through the phase optical element, designed to divide the incident beam into two closely spaced light spots, has been carried out. The simulation has been performed on the base of the finite-difference time-domain method, implemented in the software MEEP. The analysis has been shown a noticeable pattern change in the focal region using short pulses in comparison with a long signal, however, the structuring of the pulse laser beam by using the phase optical element passes successfully.
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