Dynamic Kerr effect responses in the Terahertz-range

TL;DR

This paper proposes a Terahertz-range dynamic Kerr effect experiment to probe low-frequency dynamics in disordered systems, using a Brownian oscillator model to predict frequency-dependent responses and damping effects.

Contribution

It introduces a novel field-off Kerr experiment in the Terahertz range and provides theoretical predictions for its response in disordered materials.

Findings

Frequency-selective Kerr responses are predicted.

Phonon-damping frequency dependence can be extracted.

Overdamped relaxational modes behavior is discussed.

Abstract

Dynamic Kerr effect measurements provide a simple realization of a nonlinear experiment. We propose a field-off experiment where an electric field of one or several sinusoidal cycles is applied to a sample in thermal equilibrium. Afterwards, the evolution of the polarizability is measured. If such an experiment is performed in the Terahertz-range it might provide valuable information about the low-frequency dynamics in disordered systems. We treat these dynamics in terms of a Brownian oscillator model and calculate the Kerr effect response. It is shown that frequency-selective behaviour can be expected. In the interesting case of underdamped vibrational motion we find that the frequency-dependence of the phonon-damping can be determined from the experiment. Also the behaviour of overdamped relaxational modes is discussed. For typical glassy materials we estimate the magnitude of all relevant quantities, which we believe to be helpful in experimental realizations.