Rotation of elliptic optical beam in anisotropic media

TL;DR

This paper analyzes how elliptical optical beams rotate during propagation in anisotropic media, deriving a wave equation that predicts rotation based on media anisotropy and initial beam orientation.

Contribution

It derives a wave equation for elliptical beam propagation in anisotropic media and identifies conditions for beam rotation depending on initial orientation and media properties.

Findings

Beam rotation depends on anisotropy and initial beam orientation.

A specific direction in the cross-section determines whether the beam rotates.

Rotation velocity is influenced by input beam parameters.

Abstract

We investigate the linear propagation of a paraxial optical beam in anisotropic media. We start from the eigenmode solution of the plane wave in the media, then subsequently derive the wave equation for the beam propagating along a general direction except the optic axes. The wave equation has a term containing the second mixed partial derivative which originates from the anisotropy, and this term can result in the rotation of the beam spot. The rotation effect is investigated by solving analytically the wave equation with an initial elliptical Gaussian beam for both uniaxial and biaxial media. For both media, it is found that there exists a specific direction, which is dependent on anisotropy of the media, on the cross-section perpendicular to propagation direction to determine the rotation of the beam spot. When the major axis of the elliptical spot of the input beam is parallel to or perpendicular to the specific direction, the beam spot will not rotate during propagation, otherwise, it will rotate with the direction and the velocity determined by input parameters of the beam.