Rotatum of Light

TL;DR

This paper introduces optical rotatum, a new form of structured light where optical vortices undergo a quadratic chirp in orbital angular momentum, leading to unique topological and phase properties with potential applications in various fields.

Contribution

The study presents the concept of optical rotatum, demonstrating its topological deformation, Berry phase accumulation, and characteristic logarithmic spiral structure, expanding the understanding of structured light.

Findings

Optical rotatum exhibits a quadratic chirp in orbital angular momentum.

The spatial structure follows a logarithmic spiral pattern.

Berry phase influences the propagation constant of the beam.

Abstract

Vortices are ubiquitous in nature and can be observed in fluids, condensed matter, and even in the formation of galaxies. Light, too, can evolve like a vortex. Optical vortices are exploited in light-matter interaction, free-space communications, and imaging. Here, we introduce optical rotatum; a new degree-of-freedom of light in which an optical vortex experiences a quadratic chirp in its orbital angular momentum along the optical path. We show that such an adiabatic deformation of topology is associated with the accumulation of a Berry phase factor which in turn perturbs the propagation constant (spatial frequency) of the beam. Remarkably, the spatial structure of optical rotatum follows a logarithmic spiral; a signature that is commonly seen in the pattern formation of seashells and galaxies. Our work expands previous literature on structured light, offers new modalities for light-matter interaction, communications, and sensing, and hints to analogous effects in condensed matter physics and Bose-Einstein condensates.