Anisotropic diffraction induced by orbital angular momentum during propagations of optical beams

TL;DR

This paper demonstrates that orbital angular momentum (OAM) in elliptic optical beams can induce anisotropic diffraction, with a quantitative relation established, revealing how OAM influences beam expansion, rotation, and anisotropic properties during propagation.

Contribution

It provides an analytical relation between OAM and anisotropic diffraction, showing how OAM enhances beam expansion and induces rotation in elliptic beams without phase singularities.

Findings

OAM induces anisotropic diffraction in elliptic beams.

Larger OAM results in stronger anisotropic diffraction.

OAM causes the beam to rotate with an angle up to π/2 during propagation.

Abstract

It is demonstrated that the orbital angular momentum (OAM) carried by the elliptic beam without the phase-singularity can induce the anisotropic diffraction (AD). The quantitative relation between the OAM and its induced AD is analytically obtained by a comparison of two different kinds of (1+2)-dimensional beam propagations: the linear propagations of the elliptic beam without the OAM in an anisotropic medium and that with the OAM in an isotropic one. In the former case, the optical beam evolves as the fundamental mode of the eigenmodes when its ellipticity is the square root of the anisotropic parameter defined in the paper; while in the latter case, the fundamental mode exists only when the OAM carried by the optical beam equals a specific one called a critical OAM. The OAM always enhances the beam-expanding in the major-axis direction and weakens that in the minor-axis direction no matter the sign of the OAM, and the larger the OAM, the stronger the AD induced by it. Besides, the OAM can also make the elliptic beam rotate, and the absolute value of the rotation angle is no larger than $\pi/2$ during the propagation.