Terahertz Nonlinear Index Extraction via Full-Phase Analysis

We experimentally show the spectrally averaged nonlinear refractive index and absorption coefficient for liquid water, water vapor, alpha-pinene, and Si using a full-phase analysis in the terahertz regime through a standard time-domain spectrometer. Our results confirm that the nonlinear index of refraction of the liquid samples in this regime exceeds the near-infrared optical nonlinear index by six orders of magnitude. In the case of liquid water and water vapor at atmospheric pressure, we find a nonlinear index of 7.8 x 10(-10) cm(2)/W and 6 x 10(-11) cm(2)/W, respectively, which are both much larger than expected. (C) 2020 Optical Society of America