Amplification of light and random laser action in partially ordered dye-doped nematics

Experimental evidence of random laser action in a partially ordered, dye doped nematic liquid crystal with long-range dielectric tensor fluctuations is presented. When exceeding a certain threshold pump power value, the fluorescence curve in the system collapses and distinct sharp peaks emerge above the residual spontaneous emission spectrum. Unlike distributed feedback mirror-less lasers, this nematic system can be regarded as a cavity-less microlaser where the partially ordered bulk surprisingly plays the amplifying role, acting as a randomly distributed feedback laser. Here, the unforeseen surviving of constructive interference in repeated multiple scattering events of the dye emitted photons provide the necessary optical feedback for lasing in our liquid crystalline material. The random laser emission has attractive features, such as an extremely narrow banded linewidth (0.5 nm FWHM), low emission threshold (30 mu J/mm(2)) and a very high efficiency (>20%). Different confining geometries are experimentally investigated, while obtaining intensity fluctuations of the spatially overlapping speckle-like emission patterns clearly demonstrates the typical spatio-temporal randomness of diffusive laser emission. These interesting inorganic lasing systems could represent an exceptionally promising route for fundamental prospective studies with strong technological implications for integrated optical systems, nanophotonics and optoelectronic fields.