Birefringence induced in azopolymer (PAZO) films with different thickness

In this article we present a study of the photoinduced birefringence (Δn) in films of a water soluble azopolymer: poly[1- [4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO). Varying the concentration of the azopolymer in the solution, films with wide range of thicknesses are obtained – from 50 to 2500 nm. The film thickness is determined with a Talystep precision profilometer. Birefringence is measured using a polarimetric setup with a recording laser at 473 nm and probe He-Ne laser at 633 nm. As shown experimentally, the maximal photoinduced birefringence (Δn max ) does not depend on the thickness and is of the order of 0.07 for all of the investigated samples. The recording time however considerably increases for films thicker than 500 nm.