A Dynamical Model of Harmonic Generation in Centrosymmetric Semiconductors

TL;DR

This paper models harmonic generation in centrosymmetric semiconductors, revealing how cavity environments can enhance second and third harmonic signals, with implications for nonlinear optical applications in Silicon.

Contribution

It introduces a dynamical model accounting for symmetry breaking, magnetic, and quadrupolar effects in harmonic generation, and predicts cavity-induced enhancements in Silicon.

Findings

Cavity environments significantly boost third harmonic generation.

Symmetry breaking and magnetic effects influence second harmonic angular dependence.

Phase locking enables harmonic generation despite negative dielectric function.

Abstract

We study second and third harmonic generation in centrosymmetric semiconductors at visible and UV wavelengths in bulk and cavity environments. Second harmonic generation is due to a combination of symmetry breaking, the magnetic portion of the Lorentz force, and quadrupolar contributions that impart peculiar features to the angular dependence of the generated signals, in analogy to what occurs in metals. The material is assumed to have a non-zero, third order nonlinearity that gives rise to most of the third harmonic signal. Using the parameters of bulk Silicon we predict that cavity environments can significantly modify second harmonic generation (390nm) with dramatic improvements for third harmonic generation (266nm). This occurs despite the fact that the harmonics may be tuned to a wavelength range where the dielectric function of the material is negative: a phase locking mechanism binds the pump to the generated signals and inhibits their absorption. These results point the way to novel uses and flexibility of materials like Silicon as nonlinear media in the visible and UV ranges.