Low-threshold lasing in cholesteric liquid crystals enabled by asymmetric defect layer positioning

Liquid crystal lasers are significant in photonics and applications, yet achieving low-threshold lasing remains challenging. Here, we investigate how defect positioning affects lasing performance in cholesteric liquid crystals (CLCs) with three defect layers. Simulations reveal that synchronously displacing the first two defect layers toward the third layer significantly enhances the central defect mode's density of states (DOS), particularly in asymmetric configurations near the third defect layer. This asymmetry-induced DOS enhancement boosts dye emission efficiency. Experimentally, we use wedge-shaped LC films to continuously tune defect positions and observe that asymmetric structures near the third defect layer exhibit higher lasing intensity and a lower threshold. The threshold of the asymmetric structure could be reduced by a factor of 3.4 compared to the symmetric structure. Our findings provide a strategy for low-threshold CLC lasers by leveraging defect positioning.