Difference in relaxation time between coherent and incoherent second-harmonic generation

A significant difference in relaxation time between coherent and incoherent second-harmonic generation in electric-field poled thin polymeric films has been observed experimentally. Based on the intrinsic symmetry requirements for even-order non-linear optical effects, rotational relaxation of the chromophore only was invoked in combination with translational diffusion of free volume in the polymer matrix over the coherence length for coherent second-harmonic generation and over the wavelength in the incoherent case.