Phonon-Enhanced Nonlinearities in Hexagonal Boron Nitride

TL;DR

This paper explores how strong phonon resonances in hexagonal boron nitride significantly enhance optical nonlinearities, enabling advanced time-resolved measurements and improved harmonic generation efficiencies.

Contribution

It demonstrates both experimental and theoretical evidence of phonon-induced nonlinear enhancements in hBN, including large FWM signals and increased high-harmonic efficiencies.

Findings

Large sub-picosecond FWM signals observed during resonant excitation

Enhanced third-harmonic generation at phonon resonance

Predicted significant increases in high-harmonic efficiencies

Abstract

We investigate optical nonlinearities that are induced and enhanced due to the strong phonon resonance in hexagonal boron nitride. We predict and observe large sub-picosecond duration signals due to four-wave mixing (FWM) during resonant excitation. The resulting FWM signal allows for time-resolved observation of the crystal motion. In addition, we observe enhancements of third-harmonic generation with resonant pumping at the hBN transverse optical phonon. Phonon-induced nonlinear enhancements are also predicted to yield large increases in high-harmonic efficiencies.