Longitudinal patterning of twisted light

TL;DR

This paper demonstrates the controlled longitudinal patterning of twisted light beams, specifically Frozen Waves, enabling dynamic manipulation of their orbital angular momentum and rotation characteristics along the propagation axis.

Contribution

It introduces a novel method to control the intensity and phase profiles of Frozen Waves along the propagation direction, allowing for customizable OAM behavior.

Findings

Generated rotating light patterns with controllable sense of rotation.

Achieved dynamic change of phase twist order during propagation.

Demonstrated potential for new optical manipulation techniques.

Abstract

Light beams with azimuthal phase dependence [$exp(i \ell\phi)$] carry orbital angular momentum (OAM) which differs fundamentally from spin angular momentum (SAM) associated with polarization. Striking difference between the two momenta is manifested in the allowable values: where SAM is limited to $\hbar k_0$ per photon, the OAM has unbounded value of $\ell\hbar$ per photon ($\ell$ is integer), thus dramatically exceeding the value of SAM \cite{Ref1,Ref2, Ref3}. OAM has thus been utilized in optical trapping \cite{Ref4}, imaging\cite{Ref2}, and material processing \cite{Ref5}. Furthermore, the unbounded degrees-of-freedom in OAM states have been deployed in data communications \cite{Ref6}. Here, we report an \textit{exceptional} behavior for a class of light beams---known as Frozen Waves (FWs)---whose intensity and azimuthal phase profiles can be controlled along the propagation direction, at will. Accordingly, we generate rotating light patterns that can change their sense of rotation and order of phase twist with propagation. Manipulating OAM along the beam axis can open new directions in optical science and its applications.