Optical nonlinearities of excitons in monolayer MoS2

TL;DR

This paper calculates the linear and nonlinear optical susceptibilities of monolayer MoS2, revealing strong nonlinear effects and specific polarization-dependent processes, highlighting its potential for nonlinear photonics applications.

Contribution

It derives the valley-chirality rule for second harmonic generation and analyzes polarization-dependent third-harmonic and Kerr effects in monolayer MoS2.

Findings

Efficient second harmonic generation governed by valley-chirality rule.

Third-harmonic process is efficient only with linearly polarized light.

Strong two-photon third-order nonlinearity enhances nonlinear photonics potential.

Abstract

We calculate linear and nonlinear optical susceptibilities arising from the excitonic states of mono- layer MoS2 for in-plane light polarizations, using second-quantized bound and unbound exciton operators. Optical selection rules are critical for obtaining the susceptibilities. We derive the valley-chirality rule for the second harmonic generation in monolayer MoS2, and find that the third- harmonic process is efficient only for linearly polarized input light while the third-order two photon process (optical Kerr effect) is efficient for circularly polarized light using a higher order exciton state. The absence of linear absorption due to the band gap and the unusually strong two-photon third-order nonlinearity make the monolayer MoS2 excitonic structure a promising resource for coherent nonlinear photonics.