Critical angular momentum of light

Abstract

The critical angle is the angle of incidence above which total internal reflection occurs at different dielectric interfaces, which is extensively employed in various aspects, such as optical fiber. However, these studies often limit the consideration of incident wave fields to simple fields, and complex fields, including vortex fields, are rarely investigated. In this letter, we propose the concept of critical angular momentum in optics, which characterizes the total internal reflection phenomenon for angular momentum at the interface of two different materials. Furthermore, we demonstrate theoretically and numerically that the critical angular momentum can be manipulated by introducing the rotation angle of anisotropic materials. Our original findings provide a novel way to control both momentum and angular momentum, contributing to the advancement of previous studies of critical angles.