Dye-concentration-dependent lasing behaviors and spectral characteristics of cholesteric liquid crystals

The laser behavior and spectral changes occurring in cholesteric liquid crystals with varying dye-doped concentrations were investigated when pumped at 532 nm. It was found that the long-wavelength band edge and the laser line exhibit a blue shift over 21 nm with increasing dye concentration. The circularly polarized fluorescence spectra were examined, and the location of the sense reversion of circular polarization was determined to coincide well with the discrete lasing lines. The blue shift can be ascribed to the decrease in average refractive index and pitch of the dye-doped cholesteric liquid crystals. The dependence of the slope efficiency and threshold energy on the dye concentration can be attributed to the shift in photonic stopband and the change in penetration depth of excitation. The temperature and incident angle of pumping beam also have a significant impact on the lasing properties. The optimal dye concentration is found to be 0.5 wt% at 30.5 °C with an incident angle of 10°. The laser emission located at 601.4 nm with slope efficiency of 4 % was achieved above the threshold energy of 14.3 μJ.