Photoassisted poling vs thermal poling in copolyimides for second-order nonlinear optics

Thin films of new side-chain polyimides bearing Disperse Red One (DR1) groups have been poled by the corona technique assisted by visible irradiation at low temperatures, far below the high glass transition temperature (T-g) of these polymers. The second harmonic generation (SHG) signal reached at the end of this photoassisted poling process is higher than with thermal poling. Furthermore, by a simple method based on absorption measurements with polarized light at variable incidence, it has been shown that the degradation ratio of the chromophores is much lower with photoassisted poling than with thermal poling at a temperature near T-g.