Study of laser action in dye-doped polymer dispersed cholesteric liquid crystal film

In this work, laser dye DCM, nematic liquid crystal TEB30A, chiral dopant S-811 and PVA are used to prepare polymer dispersed cholesteric liquid crystal (LC) films by the method of microcapsule. Lasing mechanism and temperature-tunable characteristics of the films are investigated. The diameters of large droplets in the films are about 80 μm and LC molecules are planar-textured in the droplets when viewed between crossed polarisers through a polarization microscope. Pumped by the 532 nm Nd:YAG laser, narrow linewidths in laser emissions are obtained at 634.5 nm and 680.2 nm, and the linewidths are of 0.25 nm and 0.29 nm, respectively. The device is then compared with a dye-doped cholesteric liquid crystal laser. The wavelength of output laser will blueshift when the temperature of the device is increased, and a 22.8 nm tunable lasing, from 666.7 nm to 643.9 nm, is obtained. Analysis concludes that the lasing mechanism of the film is band-edge lasing, and the emission wavelengths are corresponding to the two edges of the photonic band gap.