Optically induced currents in dielectrics as a nonlinear optical effect

TL;DR

This paper explains optically induced DC currents in dielectrics as a nonlinear optical effect arising from multi-photon interference, linking experimental observations to third-order susceptibilities with a simple theoretical model.

Contribution

It establishes a direct connection between observed DC currents and nonlinear optical susceptibilities, providing a simple explanation without extensive numerical simulations.

Findings

Excellent agreement with experimental data using only known third-order susceptibility of SiO2

Demonstrates that ultrafast nonlinear optical phenomena are more versatile than previously thought

Provides a physical picture of photo-induced currents based on multi-photon interference

Abstract

We show that recently observed DC currents produced by below-the-bandgap femtosecond pulses [1] can be explained as nonlinear optical effects based on multi-photon quantum interference and creation of an asymmetric distribution of virtual carriers in the conduction and valence bands. We establish an unambiguous connection between the nonlinear optical conductivity responsible for the observed DC currents and charges and the odd-order nonlinear optical susceptibilities of the material. Using a single well known measured value of the third order susceptibility (nonlinear index) of SiO2 we obtain excellent agreement with all the experimental data of [1] without resorting to extensive numerical modeling. A clear physical picture of the origin of the photo-induced currents and charges shows that the versatility of ultrafast (virtual) nonlinear optical phenomena extends even further than had been previously thought.