Azopolymer holographic diffraction gratings: Time dependent analyses of the diffraction efficiency, birefringence, and surface modulation induced by two linearly polarized interfering beams

Dynamical experimental studies of the diffraction efficiency, birefringence , and surface relief modulation were carried out on functionalized azopolym er films of p(DR1M-co-MMA) with a 12% mole fraction of DR1M. The gratings w ere recorded using two linearly polarized pump beams (lambda = 514.5 nm) ei ther;with a parallel configuration (p + p) or (s+(-s)) or with orthogonal p olarizations (p+s). A general Jones matricial approach in conjuction with r eal-time polarization analyses of the first order diffracted beam (S+1) app ears to be a quite sensitive method to extract relevant parameters such as birefringence (Delta n) and surface relief modulation (2 Delta d). The phas e matrices have been developed considering the pump polarization of the two interfering beams and taking into account the orientational "angular hole- burning" model under low pump irradiances. Numerical calculations allow us to extract the time variations of Delta n and 2 Delta d and to compare the various efficiencies in grating formation. The obtained values for Delta n are then compared with polarimetric measurements and the basic mechanisms o r driving forces in the relief formation are also discussed in connection w ith recently proposed phenomenological models.