Strong Nonlinear Response in Crystalline Quartz at THz Frequencies
Soheil Zibod, Payman Rasekh, Murat Yildrim, Wei Cui, V. R. Bhardwaj, Jean‐Michel Ménard, Robert W. Boyd, Ksenia Dolgaleva
Abstract
Abstract This study reports on the experimental observation of a very strong nonlinear response in crystalline quartz in the terahertz (THz) frequency region through THz time‐domain spectroscopy (THz‐TDS). A previously established theoretical model is modified and presented and predicts a Kerr coefficient n 2 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.