Random lasing and mode tunability by extraordinary strong and controllable scattering during the nematic-isotropic phase transition

Abstract

Random lasing emission from the lateral end face of dye doped nematic liquid crystal (DDLC) cells was investigated during the nematic-isotropic phase transition process and abundant lasing behaviors were observed. There was a temperature range of ~10 °C for the phase transition process of DDLCs, in which anisotropic light scattering was investigated. Light scattering of DDLCs was greatly enhanced during the phase transition process and the enhancement of scattering was strongly dependent on the temperature. And a peak scattering coefficient of more than 1000 cm−1 was achieved at a certain temperature, which we called the peak-scattering temperature. Random lasing induced by resonant feedback was observed near the peak-scattering temperature under the appropriate pump energies. In this situation, broad emissive spectra originating from non-resonant feedback or fluorescence were not evident. When the temperature departed from the peak-scattering value and the pump energy was fixed, the hybrid mode caused by both resonant and non-resonant feedback was achieved. And the proportion of the two feedbacks induced lasing modes could be tuned by temperature and pump energy. All the above random lasing phenomena were observed from 6-µm-thick DDLC cells. The strong scattering in the phase transition process was mainly induced by the inhomogeneity of DDLC due to coexistence of both nematic and isotropic phase. The rich lasing behaviors could be used to control lasing modes by temperature or energy of pump pulse.