Energy exchange of coherent light beams in azo-containing photosensitive polymers

The paper has presented the derivation of equations for light-induced variation of the refractive index in an azo-containing polymer from balance equations for concentrations of trans- and cis-isomers of the azo dye. The equations thus obtained help us explain the two-exponential character of the relaxation characteristics of the refractive index. The frequency dependences of an additional term to the refractive index have been obtained for harmonic intensity modulation. At frequencies above resonance ones, the equations for two-wave interaction of coherent light beams in a polymer film coincide with those derived earlier on the basis of a phenomenological model.