Random laser spectroscopy of solvent-rich polymer thin film waveguide

We present the statistical analysis of random lasing intensity fluctuations in a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminos-styryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) thin film waveguide subjected to a constant heat treatment. The microscopic changes occurring in the density of the polymer thin film during the various stages of solvent evaporation are probed using the changes in the statistics of random laser (RL) emission intensities. In the solvent rich wet film, stronger RL emission intensity fluctuations are observed compared to the dried film, leading to a relatively slower decay of the survival function distribution of the emission intensities for a mode at the gain maxima of the averaged spectrum. The mode interactions in the wet and dried films, studied using covariance between lasing mode intensities, are found to be different. Further, replica symmetry breaking studies indicate the changes in the mode interactions with the microscopic modifications in the system during solvent evaporation at a constant pump energy above the lasing threshold. The statistical analyses of the RL emission intensity fluctuations are proposed as a spectroscopic tool to probe material properties.