Random laser action in self-organized para-sexiphenyl nanofibers grown by hot-wall epitaxy

We report on the observation of amplified spontaneous emission and random lasing in self-organized crystalline para-sexiphenyl nanofibers. Using subpicosecond excitation, a lasing threshold is observed on the 0–1 emission band near 425 nm at excitation fluences as low as 0.5 $\mu {\mathrm{J/cm}}^2$ ${\text{(6×10}}^{16}\hspace{0.5em}{\mathrm{cm}}^{\text{−3}}$ equivalent density), near the onset of density-dependent recombination processes. The dependence of the nonlinear emission spectrum on both the pump intensity and position of the excitation area are attributed to the interplay between random lasing and amplified spontaneous emission occurring along the nanofibers.