Light structuring via nonlinear total angular momentum addition with flat optics

TL;DR

This paper demonstrates how nonlinear flat optics can be used to structure light in new ways by adding total angular momentum, enabling advanced control over the shape and properties of generated light.

Contribution

It introduces a novel method of structuring third-harmonic light via total angular momentum addition in nonlinear flat optics, supported by experiments and theoretical modeling.

Findings

Third-harmonic light shape is highly sensitive to pump polarization.

Total angular momentum projection is critical for analyzing structured light.

Theoretical predictions match experimental results across various pumping conditions.

Abstract

Shaping the structure of light with flat optical devices has driven significant advancements in our fundamental understanding of light and light-matter interactions, and enabled a broad range of applications, from image processing and microscopy to optical communication, quantum information processing, and the manipulation of microparticles. Yet, pushing the boundaries of structured light beyond the linear optical regime remains an open challenge. Nonlinear optical interactions, such as wave mixing in nonlinear flat optics, offer a powerful platform to unlock new degrees of freedom and functionalities for generating and detecting structured light. In this study, we experimentally demonstrate the non-trivial structuring of third-harmonic light enabled by the addition of total angular momentum projection in a nonlinear, isotropic flat optics element -- a single thin film of amorphous silicon. We identify the total angular momentum projection and helicity as the most critical properties for analyzing the experimental results. The theoretical model we propose, supported by numerical simulations, offers quantitative predictions for light structuring through nonlinear wave mixing under various pumping conditions, including vectorial and non-paraxial pump light. Notably, we reveal that the shape of third-harmonic light is highly sensitive to the polarization state of the pump. Our findings demonstrate that harnessing the addition of total angular momentum projection in nonlinear wave mixing can be a powerful strategy for generating and detecting precisely controlled structured light.