Paraxial and nonparaxial regimes of angular momentum absorption from twisted light

TL;DR

This paper develops a comprehensive theoretical model for how twisted light transfers angular momentum to absorbing disks, covering both paraxial and nonparaxial regimes, and explores how various parameters affect this transfer.

Contribution

It provides exact formulas for angular momentum transfer in different regimes and identifies size-dependent effects in the nonparaxial case, advancing understanding of light-matter angular momentum interactions.

Findings

Angular momentum transfer depends on beam parameters and object size.

In the nonparaxial regime, transfer shows staircase-like size dependence.

Results enable controlled angular momentum transfer and size-sensitive probing.

Abstract

We present a unified theoretical framework for the transfer of angular momentum from a Bessel wave of twisted light to a fully absorbing disk of finite radius. Exact expressions for the orbital angular momentum density and the total angular momentum transmitted to the disk are obtained for both paraxial and nonparaxial regimes. By varying the beam wavelength, polarization, and cone angle, several experimentally relevant regimes of angular momentum transfer are identified. In the extreme nonparaxial regime, the absorbed angular momentum displays a staircase-like dependence on the object size, which can be interpreted as a geometric Hall-type response of the twisted field. The results suggest potential applications for controlled angular momentum transfer and size-sensitive probing of absorbing objects.