scholarly journals Angular momentum of the vortex ultrashort pulsed beam with smaller beam waist

2021 ◽  
Author(s):  
Mengdi Luo ◽  
Zhaoying Wang
Keyword(s):  
Angular Momentum ◽  
Beam Waist

scholarly journals Modal coupling and crosstalk due to turbulence and divergence on free space THz links using multiple orbital angular momentum beams

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zhe Zhao ◽  
Runzhou Zhang ◽  
Hao Song ◽  
Kai Pang ◽  
Ahmed Almaiman ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Atmospheric Turbulence ◽  
Channel Capacity ◽  
Orbital Angular Momentum ◽  
Beam Waist ◽  
Modal Coupling ◽  
Divergence Effect ◽  
Power Leakage ◽  
Calm Weather ◽  
Bad Weather

AbstractOrbital-angular-momentum (OAM) multiplexing has been utilized to increase the channel capacity in both millimeter-wave and optical domains. Terahertz (THz) wireless communication is attracting increasing attention due to its broadband spectral resources. Thus, it might be valuable to explore the system performance of THz OAM links to further increase the channel capacity. In this paper, we study through simulations the fundamental system-degrading effects when using multiple OAM beams in THz communications links under atmospheric turbulence. We simulate and analyze the effects of divergence, turbulence, limited-size aperture, and misalignment on the signal power and crosstalk of THz OAM links. We find through simulations that the system-degrading effects are different in two scenarios with atmosphere turbulence: (a) when we consider the same strength of phasefront distortion, faster divergence (i.e., lower frequency; smaller beam waist) leads to higher power leakage from the transmitted mode to neighbouring modes; and (b) however, when we consider the same atmospheric turbulence, the divergence effect tends to affect the power leakage much less, and the power leakage increases as the frequency, beam waist, or OAM order increases. Simulation results show that: (i) the crosstalk to the neighbouring mode remains < − 15 dB for a 1-km link under calm weather, when we transmit OAM + 4 at 0.5 THz with a beam waist of 1 m; (ii) for the 3-OAM-multiplexed THz links, the signal-to-interference ratio (SIR) increases by ~ 5–7 dB if the mode spacing increases by 1, and SIR decreases with the multiplexed mode number; and (iii) limited aperture size and misalignment lead to power leakage to other modes under calm weather, while it tends to be unobtrusive under bad weather.

scholarly journals Determination of the beam waist position for the spin-orbit interaction effect observation

2021 ◽  
Vol 5 (45) ◽  
pp. 661-666
Author(s):  
E.A. Bibikova ◽  
N.D. Kundikova ◽  
A.A. Shulginov ◽  
N. Al-Wassiti
Keyword(s):  
Angular Momentum ◽  
Circular Polarization ◽  
Polarized Light ◽  
Longitudinal Component ◽  
Beam Waist ◽  
Orbit Interaction ◽  
Spin Orbit ◽  
Spin Orbit Interaction ◽  
Sign Change ◽  
Polarization Sign

The spin angular momentum and the extrinsic orbital angular momentum of light are associated with the polarization of light and the light propagation trajectory, respectively. Those momenta are interdependent not only in an inhomogeneous or anisotropic medium but even in free space. This interaction is called the spin-orbit interaction of light. The effects of the spin-orbit interaction of light manifest themselves in a small transverse shift of the beam field longitudinal component from the beam propagation axis in the waist region under the circular polarization sign change. They can be observed both for Gaussian beams and for structured beams. The effects of the spin-orbit interaction of light should be taken into account when nanophotonics devices are created, but the detailed investigation of the effect had not been performed yet due to the low intensity noise image of the beam waist. Precise measurements of the focal waist centerline are needed to determine the transverse shift of the beam field longitudinal component of the asymmetric converging beam's waist under the circular polarization sign change. We propose methods for determining the transverse and longitudinal positions of the beam waist. Computer image processing methods made it possible to obtain the value of the beam waist's transverse position with an accuracy of 0.1 mkm. These methods will allow further testing of the shifts' theoretical predictions, the values of which are the order of 1 mkm. The results obtained can also be used for laser processing of materials by polarized light and precise positioning of the beam's focal spot at a surface.

Spiral spectrum of multi-modified Bessel–Gaussian Schell beams in non-Kolmogorov turbulence

2016 ◽  
Vol 30 (26) ◽  
pp. 1650193 ◽  
Author(s):  
Yun Zhu ◽  
Yixin Zhang ◽  
Ye Li ◽  
Zhengda Hu
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Short Wavelength ◽  
Beam Waist ◽  
Long Wavelength ◽  
Azimuthal Index ◽  
Received Power ◽  
Rytov Approximation ◽  
Kolmogorov Turbulence ◽  
Optimal Value

On the basis of the Rytov approximation, we investigate the effects of non-Kolmogorov turbulence on the spread of the spiral spectrum and the received power of multi-modified Bessel–Gaussian Schell (MMBGS) beams carrying orbital angular momentum. Numerical results show that the spread of the spiral spectrum increases as the azimuthal index of the source increases and that an optimal value of the beam waist is obtained. We find that the spread of partially coherent MMBGS beams with short wavelength is more robust than that of beams with long wavelength. The complete reverse is true for fully coherent MMBGS beams.

Effect of the Critical Angular Momentum on Incomplete Fusion Dynamics

2015 ◽  
Vol 3 (1) ◽  
pp. 13-17
Author(s):  
D. Singh ◽  
◽  
S. Bharti Linda ◽  
Pankaj Kumar Giri ◽  
H. Kumar ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Incomplete Fusion ◽  
Critical Angular Momentum

Advanced Mode Unity Using Loop Antennas Proximate to Reflector for Orbital Angular Momentum Communication

2018 ◽  
Author(s):  
Ryohei Yamagishi ◽  
Hiroto Otsuka ◽  
Ryo Ishikawa ◽  
Akira Saitou ◽  
Hiroshi Suzuki ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Loop Antennas
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