Estimate of the coefficient of the nonlinear refractive index of crystals in the terahertz spectral region
ITMO University, Russia
A formula is derived for calculating the vibrational contribution to the coefficient of the nonlinear refractive index n_2of a crystal in terms of known crystal parameters such as the coefficient of thermal expansion, the linear refractive index and the concentration, reduced mass and the natural oscillation frequency of ions in the crystal lattice. It is shown that the value of this coefficient in the terahertz spectral region can exceed its value in the visible and near-IR spectral ranges by several orders of magnitude. Moreover, the dispersion of for crystals in the terahertz spectral range is analyzed.