Dynamics of all-optical poling of photoisomerizable molecules. II: Comparison of different angular redistribution models. Theoretical and experimental study of three-dimensional pumping

In the previous paper [J. Opt. Soc. Am. B26, 1057 (2009)], the theory of photoisomerization optical pumping cycles had been developed for three-dimensional molecules, and the evolution of tensorial properties had been simulated, with a particular attention to symmetry properties. Here different models of angular redistribution are compared—diffusion in the photoisomer or rotation in photoisomerization processes—in the case of axial molecules, with an axial symmetry of fields. The possibility of increasing χ(2), by destroying the anisotropy with a third pumping beam, is studied theoretically and experimentally. The failure of this experiment is explained by the too slow redistribution in DR1-MMA copolymers. While anisotropy measurements are unable to discriminate between the different models, the dynamics of second harmonic generation pleads for memoryless angular redistribution, with a very small probability.