How doping a cholesteric liquid crystal with polymeric dye improves an order parameter and makes possible low threshold lasing

Lasing conditions in a dye-doped cholesteric liquid crystal (ChLC) have been studied in view of optical modes for the light propagating in ChLCs using a polymeric dye with the transition dipole moment parallel to the local director of the ChLC host. We found that lasing always occurs at the lower-energy edge of the photonic gap. This is because that the optical eigen mode at the lower-energy gap is linearly polarized parallel to the director, while it is perpendicular at the higher-energy gap. Because of this well-defined lasing condition, low-threshold lasing was successfully achieved.