3D Characterization of Photo-Induced Anisotropy and All-Optical Poling of Organic Films
Most of experimental and theoretical studies of Photo-Induced Anisotropy (PIA) and All-Optical Poling (AOP) of organic films have been performed in a 2D geometry, i.e. with pumping and probing light beams almost normal to plane samples. With this geometry, only in plane anisotropy or poling can be observed. A 3D experimental arrangement is described, in which molecules may be optically pumped in two orthogonal directions and probed in three directions. The method of measurement of the 3D anisotropy is discussed and illustrated by two experiments. In the first AOP and PIA experiment, a MMA-DR1 copolymer film is pumped by two co-propagating linearly polarized coherent harmonic beams and by a third incoherent circularly polarized beam, which reduces anisotropy: the expected improvement of poling was not observed, which should initiate new theoretical works. In the second experiment, the 3D anisotropy of a thin film of evaporated small azoic molecules is studied: before any optical excitation, this film is noncentrosymmetric and very anisotropic. Optical pumping destroys this natural anisotropy and hardly tends to impose its own symmetry.
Keywords: Photo-Induced Anisotropy, All-Optical Poling, 3D characterization, Azoic dyes, MMA-DR1 copolymer, Small molecules