Parametric amplification of optical phonons

TL;DR

This paper demonstrates the experimental amplification of optical phonons in silicon carbide using a mid-infrared optical field, revealing a new mechanism for controlling phononic interactions and phase transitions.

Contribution

It provides the first experimental demonstration of optical phonon amplification via parametric gain in solids, supported by first-principles calculations.

Findings

Achieved phonon amplification across the reststrahlen band.

Identified quadratic dependence of dielectric permittivity and oscillator strength on lattice displacement.

Showed that phonon parametric gain can be extended to all polar modes in solids.

Abstract

Amplification of light through stimulated emission or nonlinear optical interactions has had a transformative impact on modern science and technology. The amplification of other bosonic excitations, like phonons in solids, is likely to open up new remarkable physical phenomena. Here, we report on an experimental demonstration of optical phonon amplification. A coherent mid-infrared optical field is used to drive large amplitude oscillations of the Si-C stretching mode in silicon carbide. Upon nonlinear phonon excitation, a second probe pulse experiences parametric optical gain at all wavelengths throughout the reststrahlen band, which reflects the amplification of optical-phonon fluctuations. Starting from first principle calculations, we show that the high-frequency dielectric permittivity and the phonon oscillator strength depend quadratically on the lattice coordinate. In the experimental conditions explored here, these oscillate then at twice the frequency of the optical field and provide a parametric drive for lattice fluctuations. Parametric gain in phononic four wave mixing is a generic mechanism that can be extended to all polar modes of solids, as a new means to control the kinetics of phase transitions, to amplify many body interactions or to control phonon-polariton waves.