Plasmonic enhanced low-threshold random lasing from dye-doped nematic liquid crystals with TiN nanoparticles in capillary tubes

We report a plasmonic enhanced low-threshold random lasing from dye-doped nematic liquid crystals with titanium nitride (TiN) nanoparticles (NPDDNLC) in capillary tubes. The NPDDNLC sample yields a coherent random laser with about 0.3 nm in the full width at half maximum (FWHM). We find the laser threshold is decreased by introducing the TiN NPs into the dye-doped nematic liquid crystal sample. The laser threshold decreases with increasing the number density of TiN nanoparticles from 5.613 x 10(10)/ml to 5.314 x 10(11)/ml. We suggest that the low-threshold random laser is caused by the cooperative effect of the recurrent multiple scattering and field enhancement in the vicinity of TiN nanoparticles. The localized electric field near the TiN nanoparticles enhances the energy absorption of the dye and strengthens the fluorescence amplification. Moreover, we provide a new parameter (the relative efficiency of the stimulated radiation photons) to quantify the quality of the random laser, and we give expressions for the wavelength, mode, and whole emission spectrum. Finally, we find the emission spectrum depends strongly on the emission angle and we discuss the reasons. These findings provide a simple and efficient way for the realization of low-threshold random lasers with low cost.