Irradiation poled polymer

Charge redistribution within the polymer sample modulates its refractive index. A future application of photorefractivity in optical computing is demonstrated by a two-beam coupling experiment. When a poled polymer film is irradiated with two incident laser beams crossing each other in the polymer, energy transfer between the two beams occurs that is, one beam loses power, the other gains an equal amount of power. 

Similar PID results have been reported in very high Tg (up to SSO C) azo-polyimides. It has been shown previously that irradiation of the donor-embedded polyimide derivatives with polarized light alone at room temperature induces a quasi-permanent nonpolar orientation, which can be thermally erased only by heating the polymer above Tg. While, the lifetimes of the polar order generated by thermal poling of the donor-embedded polyimides were found to be on the order of tens of years to centuries at room temperature, photoisomerization can efficiently depole these polymer films in a matter of minutes at room temperature. Indeed, Figure 8.6 shows the effect of p-polarized irradiation on the SH signal of PI-2, which had been previously thermally... 

Another problem is that switching of the SHG signal is possible only for a limited number of cycles the higher SHG value reached after UV irradiation decreases with the performed number of cycles. This decrease is interpreted as an effect of disorientation. Indeed, in the absence of a poling field, the chromophores have no reason to recover exactly the same orientation after one isomerization cycle. In the worst cases, the poled order is completely lost after one switching attempt. Usually, this type of disorientation occurs faster in side-chain polymers than in doped ones. ... 

The polymer used for this table was a PMMA-based side-chain polymer with DANS, with a molar ratio of DANS to MMA of 50 50. The contact electrode poling was performed at 140 C for 5 min with the poling field of 120 V//u,m, Photobleaching was performed by irradiation of UV light in an air atmosphere using a large-area illuminator [Oriel Co., 1000 W Hg(Xe) lamp] with a total intensity of 80 mW/cm for 15 h. 

---