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Propagation properties of a partially coherent anomalous hollow vortex beam in underwater oceanic turbulence
摘要： Based on the extended Huygens–Fresnel principle, the cross-spectral density function of a partially coherent anomalous hollow vortex beam (AHVB) propagating in underwater oceanic turbulence has been derived, and the influences of the beam parameters and underwater oceanic turbulence on the average intensity and coherence properties are investigated by using numerical examples. Our results show that the partially coherent AHVB with smaller coherence length and smaller M will evolve into the flat-topped faster as the propagation distance increases, and the partially coherent AHVB propagating in stronger underwater oceanic turbulence (the larger χT and ? or the smaller ε) will lose the initial dark hollow center and evolve into the Gaussian beam more rapidly. In the influences of oceanic turbulence on the spreading of partially coherent AHVB, it is found that the parameters χT and ? will cause the larger spreading than the parameter ε at the same propagation distance. This research is useful to the practical application of the partially coherent AHVB beam in underwater oceanic turbulence.
关键词： Laser propagation,Vortex beam,Dark hollow beam,Average intensity
更新于2025-09-23 15:22:29
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Coherence properties of a random electromagnetic vortex beam propagating in biological tissues
摘要： Based on the extended Huygens-Fresnel principle and the unified theory of polarization and coherence, the coherence properties of random electromagnetic Gaussian Schell model (GSM) vortex beams propagating through biological tissues were investigated. It was shown that with an increasing propagation distance, the change in the spectral degree of coherence |μ(ρ, ?ρ, z)| is more complex than that of μ(0, ρ, z). If the change in |μ(ρ, ?ρ, z)| is divided into the preceding and latter stages, then the change in μ(0, ρ, z) is similar to that of |μ(ρ, ?ρ, z)| at the latter stage. The wavelength of the far-infrared beam (λ = 10.6 μm) is similar to that emitted by the biological tissues, and a resonance with water molecules occurs in the biological tissues. At the initial plane, the larger ρx corresponds to a smaller value of |μ(ρ, ?ρ, z)|, and during the propagation process, the spatial coherent interval is wider for |μ(ρ, ?ρ, z)| than for μ(0, ρ, z). The fluctuation change depth of |μ(ρ, ?ρ, z)| in the biological tissues is somewhat shallower than that of μ(0, ρ, z) under the same conditions, such as the same biological tissue, the same wavelength, or the same interval between two field points. In addition, the spatial self-correlation length σ yy has an effect on |μ(ρ, ?ρ, z)| and on μ(0, ρ, z) to a different extent, while the changes in these two quantities are independent of the spatial mutual-correlation length σ xy of the random electromagnetic GSM vortex beam.
关键词： vortex beam,Spectral degree of coherence,cross-spectral density matrix,biological tissues
更新于2025-09-23 15:21:01
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Selection of the confining beam for laser direct writing with scanning absorbance modulation
摘要： Absorbance-modulation optical lithography has been proposed to obtain super-resolution grating patterns with far-field optics. However, the patterns are monotonous since the interference fringes are used as the confining beam. We propose laser direct writing with scanning absorbance modulation to produce free super-resolution patterns. Four kinds of optical vortex beams are studied as the confining beam and the performance of scanning absorbance modulation using each of them is simulated. In conclusion, the selection of the best confining beam has to follow three criteria and an example is the 2-level, 1.5-order optical vortex beam.
关键词： laser direct writing,optical vortex beam,absorbance modulation
更新于2025-09-23 15:19:57
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High-Efficiency Planar Reflectarray with Small-size for OAM Generation at Microwave Range
摘要： In this paper, a high-efficiency planar reflectarray with a small size 3.87λ0 × 3.87λ0 is designed, which can effectively convert arbitrary polarized waves to orbital angular momentum (OAM) waves with desired mode number and beam direction. The two concentric rings with a small size 0.38λ0 × 0.38λ0 compose the unit, which can cover the phase shifting range 360o by adjusting the ring radius. Though the developed reflectarray is much smaller than that of published ones, it can produce beams with the similar performance as large antennas. The advantages are as follows: high efficiency 22.6%, which is superior to published OAM reflectarrays, high gain 15.4 dBi, narrow divergence angle 9o, high purity, good stability, polarization insensitivity, planar structure, and easy fabrication. Using this reflective metasurface, we designed the following OAM beams: (1) OAM mode l = 1, 2, 3, 4 at (θ = 0o, φ = 0o). (2) l = 1 at (θ = 45o, φ = 180o). (3) l = 1 at (θ = 45o, φ = 270o). The above advantages are proved by the following analysis: (1) The magnitude and phase distributions in the near field. (2) The purity analysis. (3) The radiation pattern in the far field.
关键词： Orbital angular momentum (OAM),high efficiency,vortex beam,planar reflectarray antenna
更新于2025-09-19 17:15:36
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Optical twists and transverse focal shift in a strongly focused, circularly polarized vortex field
摘要： Twisting behaviors of the optical vortices and the intensity patterns of a strongly focused, circularly polarized field with two off-axis vortices are investigated in this article. The transverse focal shift (TFS) which is mainly caused by the off-axis vortices and the strong focusing effect is also studied. It is very interesting to find that in the focal region the two off-axis vortices can coil many circles with each other as the beam propagates, and their trajectories form a double helical structure. Three factors for this twisting behavior are analyzed. It is also found that the intensity maxima of the total field are not strongly influenced by the twisting behavior of the vortices and rotate only a quarter circle (90?) to the focal plane. In contrast to the TFS in the linearly polarized field, the 'actual focus/foci' in this circularly polarized field does/do not move between the +ys axis and the ?ys axis or the ys axis and the xs axis, but is/are always confined on the +ys/ys axis. These results will be useful in understanding the general rotational behaviors in optical fields with off-axis vortices and can have applications in optical manipulations.
关键词： polarization,transverse focal shift,vortex beam,phase singularity
更新于2025-09-19 17:15:36
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Electron holography for vortex beams
摘要： A combined technology of vortex beam technique and electron holography has been developed. A range of about 10 times the diameter of the grating opening was irradiated and electron holography, electron vortex beam, orbital angular momentum, helical wavefront, wave propagation two-wave interference between a Bragg diffraction wave as a vortex beam and transmitted wave from and around a fork-shaped grating was recorded as a hologram. Reconstruction by using the Fourier transform method has been simultaneously performed for amplitude and phase distributions. Furthermore, by using a wave aberration function, amplitude and phase distributions at various propagation positions were reconstructed numerically, resulting in confirmation of vortex beam twists.
关键词： helical wavefront,electron holography,electron vortex beam,orbital angular momentum,wave propagation
更新于2025-09-19 17:13:59
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Singular Atmospheric Optics: From Wavefront Dislocations to Synthesis of Vortex Laser Beams
摘要： Studies on the singular optics of scalar wave fields carried out in the world and at V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences (IAO SB RAS) are reviewed. The study results of the processes of origination and annihilation of phase singularities are generalized. The methods for singular phase reconstruction and their applicability to the problems of adaptive focusing of radiation in randomly inhomogeneous media are examined. The energy, statistical, and topological properties of vortex optical beams propagating through a turbulent atmosphere are analyzed. The results of the synthesis of vortex beams with quickly controllable orbital angular momentum by the matrix approach developed at IAO SB RAS are described.
关键词： vortex beam,turbulent atmosphere,probability density function,intensity fluctuations
更新于2025-09-19 17:13:59
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High-Efficiency and Broadband Near-Infrared Bi-Functional Metasurface Based on Rotary Different-Size Silicon Nanobricks
摘要： Several novel spin-dependent bi-functional metasurfaces consisting of different-sized rotary silicon nanobricks have been proposed and numerically investigated based on the Pancharatnam–Berry phase and structural phase simultaneously. Here, a transmission mechanism is strictly deduced, which can avoid crosstalk from the multiplexed bi-functional metasurface. Four kinds of high-efficiency including a spin-dependent bi-functional beam deflector, a spin-dependent bi-functional metalens, a bi-functional metasurface with spin-dependent focusing and deflection function, and a spin-dependent bi-functional vortex phase plate. All of the results demonstrate the superior performances of our designed devices. Our work opens up new doors toward building novel spin-dependent bi-functional metasurfaces, and promotes the development of bi-functional devices and spin-controlled photonics.
关键词： metalens,metasurface,phase modulation,vortex beam
更新于2025-09-16 10:30:52
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Combined implementation of smoothing technologies for improving illumination uniformity of laser quad in multi-directions
摘要： Azimuthal smoothing (AS) that enables the focal spot of a laser quad to rotate in a period of a few picoseconds can improve the illumination uniformity. However, the smoothing performance of azimuthal smoothing is worse than that of smoothing by spectral dispersion (SSD) due to the low rotation speed in the center area of the focal spot. A combined implementation of the schemes including smoothing by spectral dispersion, radial smoothing (RS) and azimuthal smoothing is discussed to achieve better and faster illumination uniformity. The theoretical models of the combined smoothing scheme have been built up to analyse the smoothing performance. The key parameters affecting the smoothing performance of the combined smoothing scheme are analysed and optimized, including the topological charge and the wavelength difference. The simulation results show that the illumination uniformity of the laser quad can be significantly improved in multi-directions by the combined smoothing scheme.
关键词： Inertial confinement fusion,azimuthal smoothing scheme,vortex beam,radial smoothing,uniformity,smoothing by spectral dispersion
更新于2025-09-12 10:27:22
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Optimized Chemical Potential Graphene-Based Coding Metasurface Approach for Dynamic Manipulation of Terahertz Wavefront
摘要： In this paper, a new method for the design of pixelated graphene-based coding metasurface is proposed. This method suggests a straightforward approach by utilizing graphene tunable pixels (GTP), which can control the reflection phase in a real-time manner at terahertz (THz) frequencies. The proposed unit cell is composed of four distinct graphene patches in the same layer, which has a chemical potential that obtained by utilizing optimization-based methods. By changing the reflection phase profile across the metasurface, the proposed device can manipulate the reflected wave phase, amplitude, and polarization control in various beamforming applications at THz spectrum for modern information systems, data encryption, and THz communication applications. Chemical potential optimization method in graphene-based coding metasurface is not limited to a specific structure for phase-only metasurface. Indeed it has an exceptional capability for metasurface to manipulate electromagnetic (EM) wave in the half-space and generate converged vortex beam, non-diffractive Bessel beam, and EM bump illusion. The simulation and theoretical results show that the suggested method offers a feasible strategy for multifunctional metasurface applications.
关键词： Bessel beam,Illusion,Chemical potential optimization,Vortex beam,Metasurface,Graphene
更新于2025-09-11 14:15:04