  Random lasing occurs as the result of a coherent optical feedback from
multiple scattering centers. Here, we demonstrate that plasmonic gold nanostars
are efficient light scattering centers, exhibiting strong field enhancement at
their nanotips, which assists a very narrow bandwidth and highly amplified
coherent random lasing with a low lasing threshold. First, by embedding
plasmonic gold nanostars in a rhodamine 6G dye gain medium, we observe a series
of very narrow random lasing peaks with full-width at half-maximum ~ 0.8 nm. In
contrast, free rhodamine 6G dye molecules exhibit only a single amplified
spontaneous emission peak with a broader linewidth of 6 nm. The lasing
threshold for the dye with gold nanostars is two times lower than that for a
free dye. Furthermore, by coating the tip of a single-mode optical fiber with
gold nanostars, we demonstrate a collection of random lasing signal through the
fiber that can be easily guided and analyzed. Time-resolved measurements show a
significant increase in the emission rate above the lasing threshold,
indicating a stimulated emission process. Our study provides a method for
generating random lasing in the nanoscale with low threshold values that can be
easily collected and guided, which promise a range of potential applications in
remote sensing, information processing, and on-chip coherent light sources.
