Lasing in three layer systems consisting of cholesteric liquid crystals and dye solution

We have investigated defect mode lasing in a multilayer system. consisting of a dye doped isotropic solvent sandwiched between two cholesteric liquid crystal (CLC) cells. In this case we can use dyes not soluble in liquid crystals and avoid the degradation of the CLC structure caused by the absorption of the pumping energy. When the CLC pitches of both cells are equal, the dye emission generates the typical multi-mode lasing peaks inside the photonic stop band. In CLC mixtures whose pitches were shifted one respect to the other in such a way that only the edges of band gaps of the CLC layers overlapped, we have observed single mode lasing. The divergence of the laser beam spot is considerably lower than the one observed in dye doped CLC.