# Dynamic Spatiotemporal Beams that Combine Two Independent and Controllable Orbital-Angular-Momenta Using Multiple Optical-Frequency-Comb Lines

## TL;DR

This paper introduces a numerical method to generate dynamic spatiotemporal beams that combine different forms of orbital angular momentum by coherently adding multiple optical-frequency-comb lines, enabling control over their rotation and revolution characteristics.

## Contribution

It presents a novel approach to generate and control complex dynamic beams combining multiple OAM modes using multiple frequency comb lines, advancing structured light manipulation.

## Key findings

- Achieved high modal purity (~96%) for rotating l values from +1 to +3.
- Controlled revolving speeds between 0.2-0.6 THz.
- Varied beam waist and revolving radius parameters.

## Abstract

Novel forms of beam generation and propagation based on structured light and orbital angular momentum (OAM) have gained significant interest over the past several years. Indeed, dynamic OAM can manifest at a given propagation distance in different forms , including: (1) a simple Gaussian-like beam "dot" "revolves" around an offset central axis in time, and (2) a Laguerre-Gaussian (LG) beam with a helically "twisting" phase front that "rotates" around its own central null in time. In this paper, we numerically generate dynamic spatiotemporal beams that combine these two forms of orbital-angular-momenta by coherently adding multiple frequency comb lines such that each carries a superposition of multiple LG(l,p) modes containing one l value but multiple p values. The generated beams can have different non-zero rotating l values with high modal purities that exhibit both "rotation" and "revolution" in time at a given propagation distance. In our simulation results, we were able to control and vary several parameters, including the: (i) rotating l value from +1 to +3 with modal purities of ~96%, (ii) revolving speed of 0.2-0.6 THz, (iii) beam waist of 0.15-0.5 mm, and (iv) revolving radius of 0.75-1.5 mm.

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Source: https://tomesphere.com/paper/1904.13150