Plasmon Assisted Coherent Random Lasing

Random lasing occurs as the result of a coherent optical feedback from multiple scattering centers. Here, we demonstrate that plasmonic gold nanostars, through their small tips, are efficient light scattering centers which assist very narrow bandwidth and highly amplified coherent random lasing at a low lasing threshold. First, by embedding plasmonic gold nanostars in a rhodamine 6G dye gain medium, we observed a series of very narrow random lasing peaks with full-width at half-maximum (FWHM) ~0.8 nm. By contrast, free rhodamine 6G dye exhibited only a single lasing peak with FWHM of 6 nm. The lasing threshold for the dye with gold nanostars was two times smaller than that for a free dye. Further, by coating the tip of a single-mode fiber with these nanostars, we demonstrated the collection of the random lasing signal through the fiber that can easily be guided and analyzed. Time-resolved measurements showed a significant increase in the emission rate at above the lasing threshold, indicating a stimulated emission process.