All optically induced Χ⁽²⁾ structures and their optical anisotropy in betaine dispersed in polymer matrix

This paper is concerned with the noncentrosymmetric alignment of betaine molecules dispersed in a polymeric matrix by an all-optical poling process. Two types of betaine molecules were used: one is betaine-azo with an azobenzene moiety in the molecule and the other is betaine-C8 without an azobenzene moiety in the molecule. The effect of the azobenzene moiety in the molecule on the optical poling efficiency, the formation of Χ⁽²⁾ structure, and its thermal stability was studied. Optical anisotropy of the Χ⁽²⁾ tensor components formed in the matrix in the writing process with linearly polarized beams was evaluated by rotating a sample film or rotating the polarization direction of the fundamental reading beam.