Index and relief gratings in polymer films for organic distributed feedback lasers

A styrene copolymer of 4-vinylbenzyl thiocyanate (PST-co-VBT) was employed as recording material for optical interference patterns with periods Lambda < 1 mum. Using lower intensity laser irradiation (4 mJ cm(-2), lambda = 266 nm), refractive index gratings were produced in PST-co-VBT by an U-V-induced photoisomerization SCN --> NCS. Subsequent modification of the patterns with gaseous amines yielded surface relief gratings via the formation of derivatives of thiourea. Laser irradiation with higher pulse energies (7 mJ cm(-2), lambda = 266 nm) directly produced surface relief gratings via laser ablation (modulation depth 30 nm). Also these gratings were reactive toward amine reagents and allowed a selective functionalization of the grooves of the relief ("reactive gratings"). Under selected conditions, a doubling of the grating frequency was achieved by postexposure modification with gaseous amines. Optically inscribed gratings in PST-co-VBT were employed as optical resonators for distributed feedback (DFB) lasing. With a laser dye (DCM) dissolved in PST-co-VBT, optically pumped DFB laser action was observed after inscribing index and relief gratings. The pumping threshold for lasing I-th was 250 nJ cm(-2) at lambda = 532 nm.