The Research Of Tunable Dye-doped Liquid Crystal Laser

Liquid crystal laser is a new kind of laser which the laser dye is doped into liquid crystal and the optical feedback is provided by photonic band gap or multiple scattering. Because of its special structure and excitation mechanism, liquid crystal laser has many advantages including tunable, narrow linewidth, low threshold, small size etc. Consequently, the liquid crystal laser has great prospect in optical integration, laser display, medical science and optical communication. The theory and radiation mechanism of tunable liquid crystal laser were expounded in two ways: theoretical simulation and experimental. The temperature-tunable negative dielectric liquid crystal laser, electro-tunable liquid crystal laser and dye-doped polymer dispersed liquid crystal film laser were designed and manufactured. In this paper, the dye-doped chiral nematic liquid crystal is used as the gain medium, and the radiation mechanism of the liquid crystal laser is band-edge lasing.In this paper, the structural features of planartexture chiral nematic liquid crystal is discussed based on the theory of photonic crystal, and its transmission characteristic is simulated by Berreman’s 4 × 4 matrix. Based on the theory of Bragg selective reflection, the photonic band gap(PBG) of planartexture chiral nematic liquid crystal is discussed. The dye-doped negative dielectric chiral nematic liquid crystal is used to design a temperature-tunable liquid crystal laser. The pitch of this device is measured by the wedge cell, and the result shows that the pitch increases with increasing temperature. The wavelength of output laser is found to red-shift from 614.4nm at 20°C to 662.8nm at 67°C, and the central wavelength of PBG is observed to red-shift with its width reducing from 71.2nm to 40.2nm. Two kinds of electrode are designed to apply electric field for positive and negative chiral nematic liquid crystal lasers. The electric field is perpendicular to the screw axis of positive dielectric chiral nematic liquid crystal and parallel to the screw axis of negative dielectric liquid crystal. The electro-tunable of liquid crystal laser is analyzed in terms of texture, transmission spectrum and laser output. The positive and negative chiral nematic liquid crystal lasers gain 8nm and 18.5nm tunable laser output. The method of microcapsule is used to prepare dye-doped polymer dispersed liquid crystal film laser, and its radiation mechanism and temperature tuning properties are studied. The diameters of large droplets in the film are about 80mm and LC molecules are planar texture in the droplets. Pumped by the 532 nm Nd:YAG laser, narrow linewidth laser emission is obtained at 634.5 nm and 680.2nm, and the linewidth are 0.25 nm and 0.29 nm, respectively. The wavelength of output laser produces blueshift when the temperature of device is increased, and 22.8nm tunable lasing, from 666.7nm to 643.9nm, is obtained.