Dependence of random lasing properties on the gain volume in dye doped nematic liquid crystals

Abstract

ABSTRACT In this paper, the dependence of random lasing properties on the gain volume in dye doped nematic liquid crystals was investigated. Because the pump beam was focused by a lens to excite the sample, we could change the distance Δl between the focal point and the sample to vary the gain volume. When Δl was large (for example 4 mm), a Fabry-Perot like lasing mode was observed from the emission spectra. Decreasing Δl to around zero, the lasing changed into the random mode completely. And the transition process from the Fabry-Perot like mode to the random mode when decreasing Δl was observed. The underlying mechanisms were suggested. The above observed pump volume dependent lasing properties could be used to realise the manipulation over the mode and threshold of random lasers.