# High Kerr nonlinearity of water in THz spectral range

## TL;DR

This paper reports the direct measurement of water's nonlinear refractive index in the THz range, revealing it is significantly larger than in visible and NIR ranges, with potential implications for THz applications.

## Contribution

First direct measurement of water's nonlinear refractive index in the THz range using Z-scan, showing it is orders of magnitude larger than in visible and NIR spectra.

## Key findings

- Nonlinear refractive index coefficient in water is positive.
- Value can be as large as 3.5×10^{-10} cm^2/W.
- Exceeds visible and NIR values by 6 orders of magnitude.

## Abstract

The values of the nonlinear refractive index coefficient for various materials in the terahertz frequency range exceed the ones in both visible and NIR ranges by several orders of magnitude. We report the direct measurement of the nonlinear refractive index coefficient of liquid water by using the Z-scan method with broadband pulsed THz beam. Our experimental result shows that nonlinear refractive index coefficient in water is positive and can be as large as 3.5$\times$10$^{-10}$ cm$^{2}$/W in the THz frequency range, which exceeds the ones for the visible and NIR ranges by 6 orders of magnitude.