Twist-defect-mode lasing in photopolymerized cholesteric liquid crystal

The twist defect mode (TDM) has been experimentally demonstrated in the transmission spectrum of a composite film consisting of two photopolymerized cholesteric liquid crystal (PCLC) layers. The self-organized helical structure of PCLC acts as a one-dimensional (I-D) photonic crystal, and the twist defect which is a discontinuity of the director rotation around the helix axis at an interface of two PCLC layers, induces the TDM. Optically pumped laser action based on the TDM has also been observed in a dye-doped double composite PCLC film. At a high excitation energy above the threshold, the laser action has been observed at the TDM wavelength in the middle of the I-D photonic band gap of the PCLC helical structure.