Two-beam coupling by a hot electron nonlinearity

TL;DR

This paper investigates the coherent two-beam interaction in ITO at ENZ wavelengths, revealing polarization-dependent effects and the potential for controlling ultrafast nonlinearity for advanced optical applications.

Contribution

It introduces the first study of two-beam coherent interactions in hot electron nonlinear materials like ITO at ENZ, demonstrating controllable polarization-dependent effects.

Findings

Spatial and temporal interference significantly affect nonlinearity.

Diffraction of pump light into probe direction depends on polarization.

Tuning frequency or chirp can control the nonlinear response.

Abstract

Transparent conductive oxides such as indium tin oxide (ITO) bear the potential to deliver efficient all-optical functionality due to their record-breaking optical nonlinearity at epsilon near zero (ENZ) wavelengths. All-optical applications generally involve more than one beam, but the coherent interaction between beams has not previously been discussed in materials with a hot electron nonlinearity. Here we study the optical nonlinearity at ENZ in ITO and show that spatial and temporal interference has important consequences in a two beam geometry. Our pump-probe results reveal a polarization-dependent transient that is explained by momentary diffraction of pump light into the probe direction by a temperature grating produced by pump-probe interference. We further show that this effect allows tailoring the nonlinearity by tuning frequency or chirp. Having fine control over the strong and ultrafast ENZ nonlinearity may enable applications in all-optical neural networks, nanophotonics, and spectroscopy.