Low-Threshold and Narrow Linewidth Diffusive Random Lasing in Rhodamine 6G Dye-Doped Polyurethane with Dispersed ZrO$_2$ Nanoparticles

We report on low-threshold and narrow linewidth intensity feedback random lasing in Rhodamine 6G dye-doped polyurethane with dispersed ZrO$_2$ nanoparticles. Depending on the dye/particle concentration, the lasing threshold is (6.8--15.4) MW/cm$^2$ and the linewidth is (4--6) nm. The lasing threshold as a function of nanoparticle concentration is found to follow a power law with an exponent of $-0.496 \pm 0.010$, which is within uncertainty of Burin et al.'s theoretical prediction [Phys. Rev. Lett. 87, 215503 (2001)].