Abstract

In certain types of azobenzen polyesters birefringence can be induced by irradiation with intense light of defined polarisation [1]. The induced birefringence is permanent but reversible. It is permanent in a sense that it remains stable when the pump laser is turned off and all short term relaxations ceased. The oldest sample holds its birefringence for more than five years. The direction of the birefringence can be influenced by the polarisation of the pump beam. That offers the possibility of erasing an already written value of birefringence by choosing the polarisation orthogonal to the original one.

© 1998 IEEE