Transition from amplified spontaneous emission to laser action in disordered media of R6G dye and TiO2 nanoparticles doped with PMMA polymer

Abstract

A random laser (RL) based on organic Rhodamine 6G (R6G) laser- dye and TiO2 suspended nanoparticles have been prepared with polymethylmethacrylate (PMMA) as a host. Both liquid and spray-coated homogeneous film samples of 22 μm -30 μm thickness range were use. Optimum concentrations have been determined depending on the normal fluorescence spectra which give evidence that the laser dye provides amplification and TiO2 nanoparticles act as scatter center. At the optimum concentrations, results of the random laser (RL) under second harmonic Nd: YAG laser excitation show that the values of bandwidth at full width half-maximum (FWHM) and the threshold energy are about 8 nm and 3 mJ respectively, which represent the minimum value for the liquid samples in the current research. Correspondly, these values become 12 nm and 3 mJ for film sample. The broadening that can be attributed to the concentration quenching of a laser dye at high a concentration level has been observed.