Optical Rectification by Impurities in Polar Crystals

When illuminated by an optical source, absorbing impurities in polar crystals produce a macroscopic polarization due to both the change in electric dipole moment from ground to optically excited states and a pyroelectric effect in the host lattice following thermalization of the excitation. The relevance of these mechanisms to relaxation processes is demonstrated by a measurement of the dispersion of optical rectification in LiTa${\mathrm{O}}_3$: ${\mathrm{Cu}}^{++}$ over the range of rectified frequencies from 0 to ${10}^{12}$ Hz.