Doubling the output power of dye-doped cholesteric liquid crystal lasers

Usually when optically pumped, dye-doped cholesteric liquid crystals (CLC) generate circularly polarized laser light from both directions of the lasing cell along the cholesteric helical axis. In reality, only the laser light from one direction can be utilized. In this paper, we demonstrate a simple method for doubling the laser output of a dye-doped CLC laser. The extracted laser output is nearly doubled. In experiment, we use a 6-ns, frequency-doubled Nd:YAG laser to pump the CLC lasing sample at ~20 degree incident angle. A reflector: a metal mirror or a cholesteric liquid crystal reflector is placed on the backside of the CLC sample. The reflector is in proximity contact with the CLC sample and the laser action occurs only in one direction. For the metal mirror reflector, the two orthogonal circularly polarized beams are mixed by incoherent superposition. While for the cholesteric liquid crystal reflector (same handedness as the lasing cell and highly reflective of the laser light), the enhanced laser output could also be achieved due to further stimulated amplification but the output is dominated by a single polarization state. For both cases the laser output is associated with a loss of coherence. Hence a nearly unpolarized CLC laser or a partially coherent CLC laser with nearly doubled output intensity is obtained.