Theory of the optical absorption of light carrying orbital angular momentum by semiconductors

TL;DR

This paper develops a theoretical framework for understanding how twisted light with orbital angular momentum interacts with semiconductors, predicting measurable magnetic effects at the beam center.

Contribution

It introduces a novel free-carrier theory for twisted light absorption in semiconductors, including calculations of transition matrix elements and induced magnetic fields.

Findings

Magnetic field at beam center can reach millitesla levels.

Photo-excited electron wave functions are characterized for twisted light.

Electric currents induced by twisted light are quantified.

Abstract

We develop a free-carrier theory of the optical absorption of light carrying orbital angular momentum (twisted light) by bulk semiconductors. We obtain the optical transition matrix elements for Bessel-mode twisted light and use them to calculate the wave function of photo-excited electrons to first-order in the vector potential of the laser. The associated net electric currents of first and second-order on the field are obtained. It is shown that the magnetic field produced at the center of the beam for the $\ell=1$ mode is of the order of a millitesla, and could therefore be detected experimentally using, for example, the technique of time-resolved Faraday rotation.