All-optical control of second-harmonic generation in $\beta$-BaB$_2$O$_4$ via coherent, terahertz-driven acentric lattice displacement

TL;DR

This paper demonstrates a method to dynamically control second-harmonic generation in bulk beta-barium borate using resonant terahertz pulses that induce lattice displacement, enabling significant modulation of nonlinear optical properties.

Contribution

It introduces a novel THz-driven resonant lattice displacement technique to modulate SHG in bulk materials, surpassing previous non-resonant methods.

Findings

Achieved approximately 30% modulation of SHG in beta-BaB2O4.

Modulation results from changes in phase-matching conditions, not nonlinear susceptibility.

Resonant lattice excitation offers a new approach for ultrafast nonlinear optical control.

Abstract

Dynamical control of the nonlinear optical properties of solids -- with light itself -- will be essential for future ultrafast photonic technologies. Previously, methods to modulate nonlinear processes including second-harmonic generation (SHG) have relied primarily on non-resonant light-matter interaction or photo-generation of hot electrons in nanoscale materials. However, these approaches are typically constrained by limited interaction lengths and the initial frequency conversion is relatively weak under equilibrium conditions. Here, an approximately 30\% modulation of efficient phase-matched SHG in bulk beta-barium borate (beta-BaB2O4) is achieved through transient lattice deformation by intense terahertz (THz) pulses that are tuned to resonance with an infrared-active phonon mode. The effect originates from modification of the index of refraction ellipsiod and the corresponding nonlinear phase-matching conditions, rather than from direct modulation of the nonlinear susceptibility through THz-mediated chi^(3) processes. This mechanism, of resonant selective lattice excitation, points toward novel THz-control schemes to tune the nonlinear optical response in materials.