Corona poling and real-time second-harmonic generation study of a novel covalently functionalized amorphous nonlinear optical polymer

Thin films for optical second-harmonic generation (SHG) were prepared from a newly designed and synthesized amorphous polymer that incorporated a high density of active nonlinear optical groups (p-nitroaniline as attached side groups). For alignment of the nonlinear groups a very high electric field was applied by a corona discharge to the polymer films above T_g (125 °C). The subsequent freezing process resulted in a polymer film initially exhibiting a very high second-order nonlinear coefficient, d_{3 3}=31 pm/V, measured by the Maker-fringe technique, plus excellent thermal, mechanical, and optical properties. The dynamics of polar alignment and decay, studied by in situ poling (or depoling) and SHG measurements, indicated a multiple exponential behavior with the average relaxation time somewhat longer than expected from extrapolation of the dielectric relaxations data according to the Williams-Landel-Ferry equation. The frozen-in SHG behavior at room temperature (∼100 °C below T_g) relaxed after 5 days to a stabilized value of 19 pm/V for d₃₃.