Random lasing from granular surface of waveguide with blends of PS and PMMA

Lasing from a planar waveguide with the blend of Polystyrene(PS): Poly-methylmethacrylate(PMMA) doped with tris(8-hydroxyquinolinato)aluminum(Alq(3)) and 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) was investigated. Due to phase separation of the blend of PS:PMMA during the solvent evaporation process, a waveguide with granular surface was obtained, which has 2D island-like nanostructures with diameters ranging between 200 and 400 nm and heights at about 25 nm. Pumped by a YAG laser with wavelength of 355 nm, a significant random lasing was observed. Compared to the amplified spontaneous radiation (ASE) of planar waveguides with only PMMA or PS doped with Alq3:DCJTB prepared under the same conditions, the lasing threshold of the former is decreased by about 5 times, and the full width at half maximum (FWHM) is reduced to 1.7 nm from 12~15 nm. Our experiments show a promising method to achieve lower threshold for organic lasers.