Photo-induced birefringence in DR1-doped sol–gel silica and ORMOSILs thin films

Abstract Photo-induced birefringence has been measured by a pump–probe experiment in pure silica and ORMOSILs (ORganically MOdified SILanes) thin films containing Disperse Red 1 (DR1). The films are obtained via the sol–gel process using TEOS, GLYMO and ICPTEOS as precursors. Two characteristic relaxation times have been estimated for the relaxation of the birefringence: a short time, related to the Cis ⇒ Trans isomerization of the dye molecule, which does 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.