Lasers on cholesteric liquid crystals: mode density and lasing threshold

The density of states approach [J. Bendickson et al., Phys. Rev. E 53, 4107 (1996)] was applied to a simple dielectric plate and a formula was found for the spectrum of the threshold gain for lasing. Then the validity of the same approach was verified for cholesteric liquid crystals (CLC) having helical structure. For non-absorbing CLC, the dependences were found of the minimum threshold gain on the layer thickness and the optical anisotropy of the material. The contribution of the dye absorption was discussed separately. The experimental data presented are in good agreement with threshold gain calculations.