Angular Momentum of a Photon and Phase Conjugation

TL;DR

This paper explores how phase conjugation of laser beams involves internal waves carrying doubled angular momentum, with implications for optical vortices and acoustical vortex generation, supported by theoretical analysis and proposed experiments.

Contribution

It demonstrates that phase conjugation of singular laser beams involves internal waves with doubled angular momentum, revealing new insights into vortex dynamics and optoacoustic interactions.

Findings

Phase conjugation involves internal waves with doubled angular momentum.

Optical vortices emit acoustical vortices with doubled topological charge.

Double helix spiral profiles rotate with sound frequency.

Abstract

Using the concept of an ideal phase-conjugating mirror we demonstrate that regardless of internal physical mechanism the phase-conjugation of a singular laser beam is accompanied by excitation within the mirror of internal waves which carry doubled angular momentum in order to match angular momentum conservation. For a Brillouin hypersound wavefront-reversal mirror this means that each elementary optical vortex belonging to a speckle pattern emits an acoustical vortex wave with doubled topological charge. The exact spatial profiles of light intensity and the intensity of hypersound in the vicinity of the phase singularity are obtained. These spiral profiles have a form of double helix which rotates with the frequency of sound. An optoacoustic experiment is proposed for visualization of the wavefront reversal of twisted optical beams and tunable twisted sound generation.