Time dependent analysis of the formation of a half-period surface relief grating on amorphous azopolymer films

The formation of a surface relief grating (SRG) on amorphous copolymer film s containing azobenzene chromophores in side chain positions is conducted u sing two linearly polarized interfering beams with orthogonal polarization directions (p+s). Time dependent analyses of the diffraction efficiency wer e carried out by measuring simultaneously the transmitted zero order (I(0)) as well as the first (I(+/-1)) and second (I(+/-2)) diffracted orders. Two main contributions to the diffraction efficiency are evidenced: an anisotr opic (birefringence) part coming from the normal period grating plus anothe r anisotropic and surface relief part (SRG) due to the half-period grating. The origin of the weak amplitude SRG stems from the interference of partic ular I(+/-1) diffracted orders, whose resulting polarization and angular Br agg's conditions are in accordance with the existence of a double frequency modulation. Using the matricial products of Jones, theoretical expressions of transmitted and diffracted orders are thus derived. Extracted values of the phase shifts and, therefore, of the birefringence (Deltan,Deltan') and surface relief amplitude (2 Deltad) are then compared to data from optical and topographic atomic force microscopy measurements. Time dependent calcu lations of these relevant parameters as well as analyses of the polarizatio n states of transmitted and diffracted orders are in good agreement with th e proposed model. (C) 2001 American Institute of Physics.