Method of improving optical poling efficiency in polymer films

The alignment of dye molecules in optically poled polymer films is modeled. We point out that when writing beams (fundamental and second harmonic) are linearly polarized with their polarization directions parallel, the majority of the dye molecules in a poled film are axially oriented perpendicular to the writing-beam polarization, whereas the minority are polar oriented parallel to the writing-beam polarization. Only the latter, however, contribute to the second-order nonlinearity of the film. This model is verified by experiments. Based on the model, a new method of improving optical poling efficiency is put forward.