Controlling the nonlinear optical properties of MgO by tailoring the electronic structure

TL;DR

This paper demonstrates experimentally that doping MgO with chromium enhances its second harmonic generation efficiency by altering its electronic structure, supported by DFT calculations, opening new avenues for controlling nonlinear optical properties.

Contribution

First experimental demonstration that Cr doping enhances MgO's SHG efficiency through electronic structure modification, supported by theoretical calculations.

Findings

Cr doping increases SHG efficiency in MgO

SHG enhancement depends non-linearly on dopant concentration

Electronic structure modifications facilitate surface-induced SHG

Abstract

The study of the non-linear response of matter to high electric fields has recently encompassed harmonic generation in solids at near-infrared (NIR) driving wavelengths. Interest has been driven by the prospect of ultrafast signal processing and all-optical mapping of electron wave-functions in solids. Engineering solid-state band structures to control the non-linear process has already been highlighted theoretically. Here, we show experimentally for the first time that second harmonic generation (SHG) can be enhanced by doping crystals of magnesium oxide (MgO) with chromium (Cr) atoms. We show that the degree of enhancement depends non-linearly on dopant concentration. The SHG efficiency is shown to increase when Cr dopants are introduced into pure MgO. A physical picture of the effect of Cr dopants is aided by density functional theory (DFT) calculations of the electronic structure for pure and doped samples. This work shows an unambiguous enhancement of the SHG efficiency by modifying the electronic structure. The observed effects are consistent with an electronic structure that facilitates the surface induced SHG and demonstrates a minimal angular dependence. This work highlights the potential of manipulating the electronic structure of solids to control or test theories of their non-linear optical response.