Nonlinear relaxation of polarization and optical susceptibility of dielectric particles under sudden change of external field direction

Abstract

A dilute suspension of particles with permanent electric dipole moment and additional polarizability is subject to an applied electric field which suddenly changes its magnitude and direction. The time dependent behavior of the polarization and of the optical susceptibility is described by solving the Smoluchowski equation for the orientational distribution function. Because of the change of field direction the problem is not axially symmetric but by the proper choice of coordinate system the dynamical equations can be treated in the same manner as in the case of simple field switching on or field reversal. The two independent components of polarization and the nonvanishing elements of the optical susceptibility tensor are shown to be superpositions of exponentially decaying functions of time. A fast numerical method is used to calculate the spectrum of decay rates and the amplitudes of the decaying modes. The time dependence of the difference of principal indices of refraction which produces birefringence is calculated from the difference of characteristic values of the susceptibility tensor. The relaxation behavior of polar particles with additional polarizability is compared with that of simpler polar particles.