Photoinduced birefringence and numerical solution of a new dynamic model in an amorphous copolymer containing azobenzene groups

Photoinduced birefringence is investigated in a new amorphous copolymer con taining azobenzene groups. The levels of birefringence signal are found to depend an the polarization angle between the pump beam and the probe beam, and on the ellipticity of the pump beam. Both the growth and decay processe s of the birefringence signal can be described by known biexponential equat ions. The rate constants and the amplitudes associated with the growth proc ess of the photoinduced birefringence are observed to display a linear depe ndence with the pump beam intensity. A new dynamic model of the photoinduce d birefringence is presented taking into account the contributions of both the bans and cis isomers of azobenzene groups and the local polymer segment s. The numerical treatment of this model shows good agreement with the expe rimental data in the whole writing-erasing processes of the photoinduced bi refringence conducted in our polymer samples.