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

Nonlinear optics: A surprise in store? At ultrafast data rates, the ability to use light to control things could speed information processing. However, photons tend not to interact with each other, and so a nonlinear optical material is needed and the response of such materials is typically weak. Alam et al. report a surprising finding: that indium tin oxide, a commercially available transparent conducting oxide widely used in microelectronics, exhibits a large nonlinear response. They used a wavelength regime where the permittivity of the material is close to zero and observed a large and fast nonlinear optical response. The finding offers the possibility that other, so far unexplored, materials may be out there for nonlinear optical applications. Science, this issue p. 795 Indium tin oxide is found to exhibit strong nonlinear optical functionality in a specific wavelength regime. 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.

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