Random lasing in unbounded dye-doped nematic liquid crystals

Random lasing in dye-doped nematic liquid crystals (NLCs) contained in a quartz cuvette was studied. With the pumping energy rising, random lasing with nonresonant feedback and resonant feedback emerge successively with the lasing threshold of 20 and 40 mu J, respectively. The lasing properties including fluctuation of the emission spectrum, divergence angle of emission, independence of the emission on the polarisation of the pump beam and the depolarisation of emission are distinct from those of dye-doped nematics confined in the sandwich structure cell or the capillary tube. The distinctions are associated with the thermal fluctuation of dielectric tensor since there is negligible surface anchoring for the nematics in the pump volume. This indicates that the anchoring state of NLCs is an important factor determining the random lasing properties.