ИСТИНА

Phenomena of linear and nonlinear optical activity are well known already a long time ago. Both linear and nonlinear (intensity-dependent) rotations of the polarization plane of plane-polarized light, generally, are caused by the spatial dispersion (nonlocality) of optical response of the medium. However, all studies of these effects up to the present time were performed within the framework of the slowly varying envelope (SVE) approach. The goal of our study is to include into the consideration the propagation of ultrashort pulses (also those, consisting of only several light field oscillations), which cannot be described within the SVE approach. We have formulated theoretical models of the spatial dispersion and cubic nonlinearity tensor, valid for the description of ultrashort pulse propagation, and we studied numerically the propagation of pulses with various durations by finite-difference time-domain method. The results of our studies for long pulses coincide with well- known results predicted by the analytical formulas obtained within the SVE approach. It also has been shown that the SVE approach gives wrong interpretation in case of ultrashort pulses. Apart of this, we observed a number of new phenomena, connected with the transformation of the spectrum of the pulse and the hodograph of the electric field strength vector.