Slope efficiency characteristics of mode-hop driven tunable single-mode cholesteric liquid crystal laser

We report tunable single-mode lasing with an improved slope efficiency from a cholesteric liquid crystal (ChLC) cavity with a three-layered structure. The device consists of one photopolymerized ChLC layer with a wide reflection band, another ChLC layer with a notch reflection band and a Rhodamine-6G-doped ionic liquid layer acting as the gain medium. Single-mode lasing can be obtained in this device structure because the ChLC layer with the notch reflection band strongly reflects only one of the Fabry-Perot cavity modes. Tuning of the lasing wavelength is achieved by tuning the reflection band of the notch ChLC. The device showed a maximum slope efficiency of 16%, which was found to be approximately 1.5 times larger than that of ordinary ChLC lasers doped with the pyrromethene 597 laser dye.