Two-beam coupling by a hot electron nonlinearity

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. MI-optical applications generally involve more than one beam, but, to our knowledge, the coherent interaction between beams has not previously been discussed in these materials, which have 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 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 the frequency or chirp. Having fine control over the strong and ultrafast ENZ nonlinearity may enable applications in all-optical neural networks, nanophotonics, and spectroscopy. (C) 2021 Optical Society of America

Automated summary

This study explores the optical nonlinearity of ITO at ENZ, revealing the important consequences of spatial and temporal interference in a two-beam geometry. The nonlinearity can be tailored by tuning the frequency or chirp, potentially enabling applications in all-optical neural networks, nanophotonics, and spectroscopy.