Optical Switching of $\chi^{(2)}$ in Diamond Photonics

TL;DR

This paper demonstrates optical switching of second-order nonlinear susceptibility in diamond by defect engineering, enabling control over second-harmonic generation through green illumination in nanoscale cavities.

Contribution

It introduces a method to modulate diamond's $ ext{chi}^{(2)}$ using defect states, a novel approach for nonlinear photonic device control.

Findings

Effective $ ext{chi}^{(2)}$ depends on defect electronic configuration.

Green illumination can quench and toggle $ ext{chi}^{(2)}$.

First demonstration of optical switching of $ ext{chi}^{(2)}$ in diamond.

Abstract

Diamond's unique physical properties make it a versatile materials for a wide range of nonlinear and quantum photonic technologies. However, unlocking diamond's full potential as a nonlinear photonic material with non-zero second-order susceptibility $\chi^{(2)}\neq0$ requires symmetry breaking. In this work, we use a nanoscale cavity to demonstrate second-harmonic generation (SHG) in diamond, and demonstrate, for the first time, that the magnitude of the diamond's effective $\chi^{(2)}$ strongly depends on the electronic configuration of defects in the diamond crystal, such as nitrogen vacancy centres. The modification of $\chi^{(2)}$ arises from photoionisation from the negative to neutral charge state, and is manifested by quenching of SHG upon green illumination. Toggling the green illumination allows for optical switching of the device's $\chi^{(2)}$. Optical control of $\chi^{(2)}$ by defect engineering opens the door for second-order nonlinear processes in diamond.