Electrically and all-optically controllable random lasers based on dye-doped liquid crystal films

This study elucidates electrically and all-optically controllable random lasers in dye-doped liquid crystals with adding a photoisomerizable dye. The lasing intensities and the energy thresholds of the random lasers can be electrically controlled below the Fréedericksz transition threshold or all-optically controlled sequentially with a two-step exposure of UV and green beams. The below-threshold-electric- and all-optical controllabilities of the random lasers are attributable to the effective change of the spatial fluctuation of the orientational order and thus of the dielectric tensor of LCs by changing the electric-field-aligned order of LCs below the threshold and via the isothermal nematic-isotropic phase transition of LCs, respectively; thereby changing the diffusion constant and thus the scattering strength of the fluorescence photons in their recurrent multiple scattering. This can result in the change in the lasing intensity and thus the energy threshold of the random lasers.