We present a study of optically-induced molecular relaxation and optical writing processes in a photosensitive liquid crystalline polymer, containing the azobenzene moiety in the side chain. Linear and non linear ESR spectroscopies, thermal analysis and rheology investigations carried on azo polymethacrylate (PMA) samples subjected to different thermal treatments have allowed to single out a suitable procedure to get stable, homogeneous substrates. Optical studies on micrometer length scale, adopting the selected procedure, have confirmed the stability conditions in both unaligned and aligned samples. The temperature dependence of the bit stability has been determined. The writing threshold power and writing rate have been measured. The results are discussed within the perspective of extension to the nanometer length scale.