scholarly journals Topological charge of optical vortices devoid of radial symmetry

2020 ◽  
Vol 44 (4) ◽  
pp. 510-518
Author(s):  
A.A. Kovalev
Keyword(s):  
Numerical Simulation ◽  
Topological Charge ◽  
Radial Symmetry ◽  
Laser Beams ◽  
Beam Power ◽  
Optical Vortices ◽  
Phase Retardation ◽  
Beam Asymmetry ◽  
Angular Momenta ◽  
Theoretical Predictions

Here we theoretically obtain values of the topological charge (TC) for vortex laser beams devoid of radial symmetry: asymmetric Laguerre-Gaussian (LG) beams, Bessel-Gaussian (BG) beams, Kummer beams, and vortex Hermite-Gaussian (HG) beams. All these beams consist of conventional modes, namely, LG, BG, or HG modes, respectively. However, all these modes have the same TC equal to that of a single constituent mode n. Orbital angular momenta (OAM) of all these beams, normalized to the beam power, are different and changing differently with varying beam asymmetry. However, for arbitrary beam asymmetry, TC remains unchanged and equals n. Superposition of just two HG modes with the adjacent numbers (n, n+1) and with the phase retardation of (pi)/2 yields a modal beam with the TC equal to – (2n+1). Numerical simulation confirms the theoretical predictions.

scholarly journals Orbital angular momentum and topological charge of a Gaussian beam with multiple optical vortices

2020 ◽  
Vol 44 (1) ◽  
pp. 34-39
Author(s):  
A.A. Kovalev ◽  
V.V. Kotlyar ◽  
D.S. Kalinkina
Keyword(s):  
Numerical Simulation ◽  
Angular Momentum ◽  
Gaussian Beam ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Optical Axis ◽  
Random Phase ◽  
Beam Power ◽  
Optical Vortices ◽  
Local Intensity

Here we study theoretically and numerically a Gaussian beam with multiple optical vortices with unitary topological charge (TC) of the same sign, located uniformly on a circle. Simple expressions are obtained for the Gaussian beam power, its orbital angular momentum (OAM), and TC. We show that the OAM normalized to the beam power cannot exceed the number of vortices in the beam. This OAM decreases with increasing distance from the optical axis to the centers of the vortices. The topological charge, on the contrary, is independent of this distance and equals the number of vortices. The numerical simulation corroborates that after passing through a random phase screen (diffuser) and propagating in free space, the beams of interest can be identified by the number of local intensity minima (shadow spots) and by the OAM.

scholarly journals Topological Charge and Asymptotic Phase Invariants of Vortex Laser Beams

Photonics ◽  
2021 ◽  
Vol 8 (10) ◽  
pp. 445
Author(s):  
Alexey A. Kovalev ◽  
Victor V. Kotlyar ◽  
Anton G. Nalimov
Keyword(s):  
Numerical Simulation ◽  
Data Transmission ◽  
Topological Charge ◽  
Light Field ◽  
Observation Point ◽  
Laser Beams ◽  
Optical Data ◽  
Optical Signals ◽  
Asymptotic Phase ◽  
Ring Approximation

It is well known that the orbital angular momentum (OAM) of a light field is conserved on propagation. In this work, in contrast to the OAM, we analytically study conservation of the topological charge (TC), which is often confused with OAM, but has quite different physical meaning. To this end, we propose a huge-ring approximation of the Huygens–Fresnel principle, when the observation point is located on an infinite-radius ring. Based on this approximation, our proof of TC conservation reveals that there exist other quantities that are also propagation-invariant, and the number of these invariants is theoretically infinite. Numerical simulation confirms the conservation of two such invariants for two light fields. The results of this work can find applications in optical data transmission to identify optical signals.

scholarly journals Thermal defocusing of intense hollow Gaussian laser beams in atmosphere

2013 ◽  
Vol 31 (3) ◽  
pp. 403-410 ◽  
Author(s):  
Ashutosh Sharma ◽  
Mahendra Singh Sodha ◽  
Shikha Misra ◽  
S.K. Mishra
Keyword(s):  
Numerical Simulation ◽  
Urban Environments ◽  
Laser Beams ◽  
Beam Power ◽  
Dimensionless Form ◽  
High Power Laser ◽  
Power Laser ◽  
Hollow Beam ◽  
Rural And Urban ◽  
Absorption Window

AbstractIn this paper, the authors have presented a paraxial theory for propagation of (1) Gaussian (2) dark hollow Gaussian high power laser beams in the atmosphere, considering the nonlinearity arising from the temperature variation along the wave-front. Specifically, the focusing parameter for both beams has been evaluated as a function of distance and initial beam power and width (corresponding to radiation of wavelengths 1.045 µ, 1.625 µ, and 2.141 µ in the water absorption window) for the maritime, desert, rural, and urban environments as modeled at NRL; the results have been presented in the dimensionless form. It is seen that in all four environments a dark hollow beam defocuses less than the corresponding Gaussian beam of same radius and power. It is suggested that this conclusion based on the paraxial theory be verified by numerical simulation.

scholarly journals Optical beams with an infinite number of vortices

2021 ◽  
Vol 45 (4) ◽  
pp. 490-496
Author(s):  
V.V. Kotlyar
Keyword(s):  
Angular Momentum ◽  
Cross Section ◽  
Data Transmission ◽  
Topological Charge ◽  
Laser Beams ◽  
Optical Data ◽  
Optical Vortices ◽  
Straight Line ◽  
Phase Singularities ◽  
Light Beams

In optical data transmission with using vortex laser beams, data can be encoded by the topo-logical charge, which is theoretically unlimited. However, the topological charge of a single sepa-rate vortex is limited by possibilities of its generating. Therefore, in this work, we analyze light beams with an unbounded (countable) set of optical vortices. The summary topological charge of such beams is infinite. Phase singularities (isolated intensity nulls) in such beams typically have a unit topological charge and reside equidistantly (or not equidistantly) on a straight line in the beam cross section. Such beams are form-invariant and, on propagation in space, change only in scale and rotate. Orbital angular momentum of such multivortex beams is finite, since only a finite number of optical vortices fall into the area, where the Gaussian beam has a notable intensity. Other phase singularities are located in the periphery (and at the infinity), where the intensity is almost zero.

scholarly journals Self-compression of two co-propagating laser pulse having relativistic nonlinearity in plasma

2017 ◽  
Vol 35 (4) ◽  
pp. 722-729
Author(s):  
S. Kumar ◽  
P. K. Gupta ◽  
R. K. Singh ◽  
R. Uma ◽  
R. P. Sharma
Keyword(s):  
Laser Beam ◽  
Pulse Width ◽  
Pulse Compression ◽  
Group Velocity Dispersion ◽  
Refractive Index Profile ◽  
Intense Laser ◽  
Laser Beams ◽  
Critical Parameters ◽  
Beam Power ◽  
Laser Beam Intensity

AbstractThe study proposes a semi-analytical model for the pulse compression of two co-propagating intense laser beams having Gaussian intensity profile in the temporal domain. The high power laser beams create the relativistic nonlinearity during propagation in plasma, which leads to the modification of the refractive index profile. The co-propagating laser beams get self- compressed by virtue of group velocity dispersion and induced nonlinearity. The induced nonlinearity in the plasma broadens the frequency spectrum of the pulse via self-phase modulation, turn to shorter the pulse duration and enhancement of laser beam intensity. The nonlinear Schrodinger equations were set up for co-propagating laser beams in plasmas and have been solved in Matlab by considering paraxial approximation. The propagation characteristics of both laser beams inside plasma are divided into three regions through the critical divider curve, which has been plotted between pulse width τ01 and laser beam power P01. Based on the preferred value of critical parameters, these regions are oscillatory compression, oscillatory broadening, and steady broadening. In findings, it is observed that the compression of the laser beam depends on the combined intensity of both beams, plasma density, and initial pulse width.

scholarly journals The investigation of the features optical vortices focusing by ring gratings with the variable height using high-performance computer systems

2021 ◽  
Vol 2086 (1) ◽  
pp. 012166
Author(s):  
D A Savelyev
Keyword(s):  
High Performance ◽  
Focal Spot ◽  
Fdtd Method ◽  
Spot Size ◽  
Laser Beams ◽  
Optical Vortices ◽  
Focal Spot Size ◽  
Near Zone ◽  
High Performance Computer ◽  
Difference Time

Abstract The diffraction of vortex laser beams with circular polarization by ring gratings with the variable height was investigated in this paper. Modelling of near zone diffraction is numerically investigated by the finite difference time domain (FDTD) method. The changes in the length size of the light needle and focal spot size are shown depending on the type of the ring grating.

scholarly journals Topological charge and angular momentum of light beams carrying optical vortices

2004 ◽  
Author(s):  
M S Soskin ◽  
V N Gorshkov ◽  
M V Vasnctsov ◽  
J T Malos ◽  
N R Heckenberg
Keyword(s):  
Angular Momentum ◽  
Topological Charge ◽  
Optical Vortices ◽  
Light Beams
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