Dynamics of all-optical poling of photoisomerizable molecules. I. Symmetries of tensorial properties

摘要

All-optical poling (AOP) of dye molecules in polymeric materials is the result of noncentrosymmetric angular hole burning (AHB: selective depletion in the angular distribution of molecules) and of angular redistribution (AR: rotation in the reversible photoisomerization). Many publications describe successfully the photoinduced anisotropy of rodlike molecules: the cumulative building of anisotropy, after many cycles, is a necessary condition of efficiency. Other publications show the important role of the tensorial properties of molecules and fields in AOP, but they consider neither the saturation of AHB, nor AR, in multiple cycles. Here, the tensorial expression of the excitation probability, for any geometry of molecules and fields, is reevaluated (density matrix formalism) and introduced in optical pumping equations, which are solved formally (at second order) and numerically. The expected symmetries are preserved, but the saturation of optical pumping introduces new tensorial couplings, which modify chi((1)) and chi((2)).