The optically induced birefringence in different block copolymers containing azobenzene and mesogen side groups has been studied with holographic methods. In the materials, the light-sensitive blocks carrying the azobenzene moieties are embedded in a matrix of polystyrene. This has the advantage that the reorientation of the chromophores does not lead to the formation of surface relief gratings. In addition, it is possible to reduce the macroscopic chromophore concentration to any desired value while, at the same time, maintaining the stabilization effect due to cooperative reorientation of the chromophores inside the photo-addressable phases. These short-range interactions give rise to long-term stability of the inscribed gratings. Angular multiplexing of holographic plane-wave gratings as well as of two-dimensional images has been demonstrated in samples with thicknesses up to 1.1 mm. The achievable refractive-index modulation, the photo-sensitivity, and the stability of the inscribed gratings were compared for different materials. In contrast to photopolymers, our materials do not exhibit shrinkage upon illumination. Instead, a weak light-induced volume expansion was detected and studied in detail.

Date Published: 1 September 2005
PDF: 10 pages
Proc. SPIE 5939, Organic Holographic Materials and Applications III, 593908 (1 September 2005); doi: 10.1117/12.616717

Published in SPIE Proceedings Vol. 5939:
Organic Holographic Materials and Applications III
Klaus Meerholz, Editor(s)