Extremely large nonlinear response in crystalline quartz at THz frequencies

TL;DR

This paper reports the first experimental observation of an extremely large nonlinear response in crystalline quartz at THz frequencies, revealing significant nonlinear effects and saturation behavior with potential implications for nonlinear optics.

Contribution

It presents the first experimental measurement of a giant nonlinear response in crystalline quartz at THz frequencies, supported by theoretical modeling and analysis.

Findings

Nonlinear Kerr coefficient n2 ≈ 5.17×10^-14 m^2/W

Nonlinear refractive index on the order of 10^-13 m^2/W

Negative fifth-order susceptibility around 10^-30 m^4 V^-4

Abstract

We report on the first experimental observation of a very strong nonlinear response in crystalline quartz in the terahertz (THz) frequency region through THz time-domain spectroscopy (THz-TDS). Theoretical modelling is presented and predicts a Kerr coefficient n2 equal to 5.17*10^-14 m^2 W^-1. The time-domain analysis of the measured data shows that with increasing of the THz peak amplitude, the pulse experiences a larger time delay in the sample. As the THz amplitude increases to values higher than 110 kV cm^-1, the growth rate of the delay decreases, indicating a saturation process. The value of the nonlinear refractive index calculated through the frequency response analysis is estimated to be on the order of 10^-13 m^2 W^-1, which is several orders of magnitude larger than typical values of the nonlinear refractive index of solids in the visible region. Furthermore, a negative fifth-order susceptibility on the order of 10^-30 m^4 V^-4 is measured.