Second harmonic generation due to spatial structure of radiation beam

TL;DR

This paper demonstrates that spatially structured radiation can generate second harmonic signals in homogeneous 2D systems due to non-local electric responses, enabling new control over harmonic generation beyond crystal symmetry constraints.

Contribution

The authors develop an analytical theory for second harmonic generation in 2D systems with structured light, revealing effects like angular momentum doubling and broadening harmonic generation possibilities.

Findings

Structured radiation induces second harmonic in homogeneous 2D systems.

Angular momentum of light doubles in second harmonic emission.

Theory enables second harmonic generation beyond crystal symmetry limits.

Abstract

We show that spatially structured radiation generates second harmonic in a two-dimensional system even if the system is homogeneous and isotropic. The effect originates from non-locality of electric response to structured electromagnetic field. We develop an analytical theory of such a second harmonic generation in conducting two-dimensional systems. For the general type of structured radiation, we calculate the emerging electric currents at the double frequency and the emitted second harmonic radiation. The theory applied to twisted light reveals that the angular momentum of light doubles in the second harmonic emission. Our results pave the way for second harmonic generation and structuring in two-dimensional materials beyond the constraints imposed by crystal symmetry.