Thermally induced surface relief gratings in azobenzene polymers

Recently, Ramanujam and co-workers described for the first time that surfac e relief gratings can be inscribed into azobenzene copolymers with a single pair of nanosecond laser pulses. We performed a detailed investigation of the involved processes. Two contributions to the diffraction efficiency are observed, one arising from a surface relief and one from a transient cis-t rans grating which decays on millisecond time scales. The stable surface re lief, in contrast, is caused by a thermal effect which sets in at a well-de fined threshold value of the pulse energy. (C) 2000 American Institute of P hysics. [S0021-9606(00)70613-1].