Photochromism in thin films containing azodyes

Summary form only given, as follows. Dynamic holography is used to determine the response times in the trans-cis-trans photoisomerization process in azodyes embedded in a solid polymeric matrix. For the studied azo chromophore DR1 embedded in the polystyrene matrix, we have found relatively fast, under 1 ms, response time for the writing process. The experiments were performed on freestanding films using a pulsed picosecond laser for grating writing and a CW laser for reading it. It has been found that the writing process may be well described by a mono-exponential curve with a time constant below 1 ms, while the decay process is more complicated and can be approximated by a biexponential equation with two response times significantly larger than for the writing process. This time constant depends by the dye concentration and the beam intensities.