Transverse linear and orbital angular momenta of beam waves and propagation in random media

Abstract

For paraxial propagation of scalar waves the classic electromagnetic theory definition of transverse linear (TLM) and orbital angular (OAM) momenta of the beam wave are represented in terms of the coherence function. We show in examples that neither the presence of optical vortices is necessary for the intrinsic OAM, nor does the presence of optical vortices warrant the non-zero intrinsic OAM. The OAM is analyzed for homogeneously coherent and twisted partially coherent beam waves. A twisted Gaussian beam has an intrinsic OAM with a per-unit power value that can be continuously changed by varying the twist parameters. Using the parabolic propagation equation for the coherence function, we show that both total TLM and OAM are conserved for the free-space propagation, but not for propagation in an inhomogeneous medium. In the presence of the random inhomogeneous medium, the total TLM and OAM are conserved in average, but the OAM fluctuations grow with the propagation path. This growth is slower for beams with rotation-symmetric irradiance.

Twisted space-frequency and space-time partially coherent beams

“…Equation ( 4 ) has the same basic form as a spatially twisted GSM beam 9 , 10 , 12 , 14 , 37 ; however, here, space and frequency are statistically twisted. It is well known that the spectral density of a spatially twisted stochastic source rotates as the beam propagates.…”

“…Although evident from the numerous references describing rotating coherent beams 28 , 37 – 39 , it is important to point out that beam rotation does not imply partial coherence. Rotation, therefore, is a characteristic of partially coherent twisted beams, not a defining characteristic.…”

Orbital Angular Momentum Wave Generation and Multiplexing: Experiments and Analysis Using Classical and Quantum Optics

“…Scintillation index reduces with the increase of the topological charge it makes OAM beam, propagating longer distances [45], but mode scattering increases for higher order modes. Angular momenta is conserved for the free-space propagation [62] but not for an inhomogeneous medium. Scintillation severely impacts the operation of target designation [63] experiments done on the model simulations of discontinuity of statistical variations of atmospheric conditions.…”

Study on the Relationship Between Symmetric Property of Optical Orbital Angular Momentum Spectrum and Critical Points of Phase in an Inhomogeneous Non-Random Media

“…For quite a long time, it was believed that there exists a close interconnection between the spiral spectrum and phase vortex structures. However, Charnotskii's recent research showed that such a connection does not exist [5]. A tricky scenario is propagation in inhomogeneous media.…”

“…The properties of turbulence can be described through the statistical moment of fluid parameters [10]. Consequently, by introducing statistical theory and assuming the media to be statistically homogeneous, it is deduced that the ensemble average of total OAM is conserved [5,9], while the spiral spectrum demonstrates a symmetric distribution with respect to the original [6][7][8]. Darryl J. Sanchez and Denis W. Oesch tentatively discussed the physical mechanism of the phenomenon: the kinetic energy of free turbulence dissipates as heat, which makes the spatial distribution of RI in turbulence inhomogeneous.…”