Large optical nonlinearity of indium tin oxide in its epsilon-near-zero region

TLDR

Nonlinear optical phenomena are essential for applications such as microscopy, all‑optical data processing, and quantum information, yet most materials exhibit weak nonlinearity even under intense illumination. The study demonstrates that indium tin oxide attains an ultrafast, large intensity‑dependent refractive index near its epsilon‑near‑zero wavelength. The material exhibits a reversible refractive‑index change of 0.72 ± 0.025 (170 % of the linear value) with a 360‑fs recovery time, enabling ultrafast nonlinear responses for nanophotonics.

Abstract

Nonlinear optical phenomena are crucial for a broad range of applications, such as microscopy, all-optical data processing, and quantum information. However, materials usually exhibit a weak optical nonlinearity even under intense coherent illumination. We report that indium tin oxide can acquire an ultrafast and large intensity-dependent refractive index in the region of the spectrum where the real part of its permittivity vanishes. We observe a change in the real part of the refractive index of 0.72 ± 0.025, corresponding to 170% of the linear refractive index. This change in refractive index is reversible with a recovery time of about 360 femtoseconds. Our results offer the possibility of designing material structures with large ultrafast nonlinearity for applications in nanophotonics.