High-harmonic generation from subwavelength silicon films

TL;DR

This study demonstrates high-harmonic generation from a subwavelength silicon film, combining experimental observations with a comprehensive theoretical model to explain nonlinear optical processes up to the 7th harmonic in the UV range.

Contribution

It provides the first experimental evidence of high-order harmonic generation from silicon films and introduces a hydrodynamic-Maxwell model that captures complex nonlinear effects.

Findings

Harmonics generated up to the 7th order in the UV range.

Theoretical model explains surface, magnetic nonlinearities, and plasma effects.

Efficient high-harmonic generation observed at high peak power densities.

Abstract

Recent years have witnessed significant developments in the study of nonlinear properties of various optical materials at the nanoscale. However, in most cases experimental results on harmonic generation from nanostructured materials are reported without the benefit of suitable theoretical models and appropriate comparisons to assess enhancement of conversion efficiencies compared to the intrinsic properties of a given material. Here, we report experimental observations of even and odd optical harmonics generated from a suspended subwavelength silicon film, a dielectric membrane, up to the 7th harmonic tuned deep in the UV range at 210nm, which is the current limit of our detection system, using peak power densities of order 3TW/cm^2. We explain the experimental data with a time domain, hydrodynamic-Maxwell approach broadly applicable to most materials. Our approach accounts simultaneously for surface and magnetic nonlinearities that generate even optical harmonics, as well as linear and nonlinear material dispersions beyond the third order to account for odd optical harmonics, plasma formation, and a phase locking mechanism that makes the generation of high harmonics possible deep into the UV range, where semiconductors like silicon start operating in a metallic regime.