Phase gratings in photoreactive polymers: A way to optically pumped organic lasers

Poly-(4-vinylbenzyl-thiocyanate) (PVBT) was investigated as a photoreactive polymer which changes its refractive index upon UV irradiation as is requi red for the production of phase gratings. After UV irradiation, the refract ive index of PVBT films increased from n(D)(20) = 1.629 to n(D)(20) = 1.660 (Deltan = +0.031). The change in the refractive index resulted mainly from the photoinduced isomerization of thiocyanate (SCN) to isothiocyanate (NCS ) groups. It was possible to modify irradiated PVBT with 1-naphthylmethyl a mine which lead to a further increase of the refractive index. Both the iso merization and the modification were followed with FTIR spectroscopy. This modification of the irradiated zones also yields an advantageous stabilizat ion of phase gratings enscribed in PVBT. The investigations were carried ou t in the realm of novel organic distributed feedback (DFB) lasers.