Lasing from dye-doped planar cholesteric liquid crystal devices

Abstract

The lasing action of dye doped cholesteric liquid crystal (CLC) cell was investigated in this work. A planar state was prepared by antiparallel rubbing process ITO glasses with polymide layer coating. The dye doped cholesteric liquid crystal mixture was used by mixing a laser dye DCM, a chiral agent CB15 and a nematic liquid crystal TEB30A. A second harmonic Q-switched Nd:YAG pulsed laser (λ=532nm) was used as the pumping source. A sharp peak was measured at 611 nm in the cell-normal direction and cell-plane direction after reaching threshold pump energy. The least full width of half maximum (FWHM) were about 10 nm and 12 nm. The optical structure of the device was investigated upon applied voltage. The results show that planar state of the CLCs is a prerequisite for the generation of lasing emission. So laser emission attributed to the photonic band gap (Bragg mode) in the cell-normal direction in which the helical axis exists. Due to the waveguide structure formed by the liquid crystal sandwiched between glass substrates (n_e=1.522, n_o=1.692>n_g=1.50), quasi-in-plane leaky lasing modes exist in the cell-plane direction.