Photo-induced birefringence has been measured by a pump-probe experiment in
pure silica and ORMOSILs (ORganically MOdified SILanes) thin films contain
ing Disperse Red I (DR1). The films are obtained via the sol-gel process us
ing TEOS, GLYMO and ICPTEOS as precursors. Two characteristic relaxation ti
mes have been estimated for the relaxation of the birefringence: a short ti
me, related to the Cis --> Trans isomerization of the dye molecule, which d
oes not depend on the hosting matrix, and a longer time, due to the angular
diffusion towards the isotropy, strongly sensitive to the chemical bonding
of the DR1 molecule with the host. (C) 2000 Elsevier Science B.V. All righ
ts reserved.