Dye-doped Cholesteric Liquid Crystal Laser Research Articles

Lasing stability of quasi-CW driven cholesteric liquid crystal lasers

Lasing stability in dye-doped cholesteric liquid crystal (ChLC) lasers largely depends on repetition frequency of the pumping laser, and therefore stabilization of output power under quasi-continuous-wave operation with high repetition frequency greater than 1 kHz is a tough challenge. In this study, a significant improvement of lasing stability in dye-doped ChLC lasers is obtained by lowering dye concentration, increasing cell gap, and moving LC cells with a piezo stage. Considering the balance between lasing stability and slope efficiency, the optimal conditions regarding cell gap and dye concentration in a ChLC laser doped with Pyrromethene 597 are determined to be 50 μm and 0.3 wt%, respectively. Under severe conditions of high repetition frequencies of 1 kHz and 10 kHz, the optimized ChLC laser demonstrates durability retaining 100% and more than 72% against the initial output power for 30 min, respectively.

Study of laser action in dye-doped polymer dispersed cholesteric liquid crystal film

In this work, laser dye DCM, nematic liquid crystal TEB30A, chiral dopant S-811 and PVA are used to prepare polymer dispersed cholesteric liquid crystal (LC) films by the method of microcapsule. Lasing mechanism and temperature-tunable characteristics of the films are investigated. The diameters of large droplets in the films are about 80 μm and LC molecules are planar-textured in the droplets when viewed between crossed polarisers through a polarization microscope. Pumped by the 532 nm Nd:YAG laser, narrow linewidths in laser emissions are obtained at 634.5 nm and 680.2 nm, and the linewidths are of 0.25 nm and 0.29 nm, respectively. The device is then compared with a dye-doped cholesteric liquid crystal laser. The wavelength of output laser will blueshift when the temperature of the device is increased, and a 22.8 nm tunable lasing, from 666.7 nm to 643.9 nm, is obtained. Analysis concludes that the lasing mechanism of the film is band-edge lasing, and the emission wavelengths are corresponding to the two edges of the photonic band gap.

Cholesteric liquid crystal holographic laser

A new type of lasing was obtained on the basis of a dye-doped cholesteric liquid crystal laser with transversally distributed excitation. Two coherent beams of the pumping laser formed an interference pattern in the planar dye-doped cholesteric layer and provided laser generation in the separate narrow strips of the pumped area. Each of the strips demonstrated lasing along the cholesteric axis. But, due to the mutual coherence of the separate strips emission, the total picture of lasing represented an interference pattern. Thus, in contrast to the conventional lasers, the intensity distribution in the laser emission pattern had a periodical character similar to diffraction from an elementary dynamic hologram.

Tunable capability of dye-doped cholesteric liquid crystal lasers

Based on the fact that helical pitch and average refractive index of a cholesteric liquid crystal is electric-tunable and temperature-tunable, we have designed dye-doped cholesteric liquid crystal (CLC) lasers. First, the effects of the concentration of chiral and the temperature on helical pitch are investigated. Next, we gain the relationship of tunable laser with temperature and electric field. When the temperature is changed from 23 to 35℃, the wavelength shift of the lasing peak vasies from 618.90 to 594.76 nm, nearly 24.14 nm in total; when the electric field is changed from 0 to 9 V, the wavelength shift of the lasing peak ehanges from 617.40 to 608.11 nm, nearly 9.29 nm in total.

Circularly polarized high-efficiency cholesteric liquid crystal lasers with a tunable nematic phase retarder

A high efficiency dye-doped cholesteric liquid crystal (CLC) is demonstrated by optimizing the dye concentration and using an electrically tunable nematic liquid crystal (NLC) phase retarder. The state of polarization of laser emission in CLC lasers, contrary to our expectations, due to the refractive index mismatch at the boundaries is not exactly circular. A double-cell structure including a CLC laser and an adjustable NLC phase retarder with a mirror reflector on one of the inner surfaces not only purifies the polarization state of the laser output but also improves the laser efficiency by 6.7X, over the single-direction dye-doped CLC laser.

Experimental Investigation of Laser Emission of Dye-Doped Cholesteric Liquid Crystals with a Cholesteric Reflector

Dye-doped cholesteric liquid crystal (CLC) behaves like a one-dimensional photonic crystal laser when pumped by a second harmonic Nd-YAG pulsed laser. Usually circularly polarized laser light in the same sense as the cholesteric helix is emitted from both directions of the lasing cell. In this paper, we experimentally demonstrate the laser emission enhancement and investigate the corresponding polarization state from the dye-doped CLC laser in stack with another CLC reflector. Cell gap and dye concentration are important factors affecting the optical efficiency of the CLC lasers.

Tuning the photonic band gap in cholesteric liquid crystals by temperature-dependent dopant solubility

We have investigated the physical and optical properties of the left-handed chiral dopant ZLI-811 mixed in a nematic liquid crystal (LC) host BL006. The solubility of ZLI-811 in BL006 at room temperature is ~24 wt%, but can be enhanced by increasing the temperature. Consequently, the photonic band gap of the cholesteric liquid crystal (CLC) mixed with more than 24 wt% chiral dopant ZLI-811 is blue shifted as the temperature increases. Based on this property, we demonstrate two applications in thermally tunable band-pass filters and dye-doped CLC lasers.

Incident angle and polarization effects on the dye-doped cholesteric liquid crystal laser

Polarization effect of the pulsed pumping laser on the lasing characteristics of the dye-doped right-handed cholesteric liquid crystal (CLC) is studied at different incident angles. At a small incident angle (<18°), the CLC laser performance is independent of the polarization state of the pumping laser. As the incident angle exceeds 18°, the CLC laser emission strongly depends on the polarization state of the pumping laser. As the incident angle increases, the lasing efficiency of the CLC laser is dramatically decreased for those excited by the right-handed circularly polarized or linearly polarized laser, but barely affected by the left-handed circularly polarized laser. As the incident angle exceeds ∼31°, lasing phenomenon diminishes under the excitation of the right-handed circularly polarized laser. The lasing threshold pumped by the linearly polarized laser is ∼2× higher than that pumped by the left-handed circularly polarized laser.

Laser emission from a dye-doped cholesteric liquid crystal pumped by another cholesteric liquid crystal laser

We report the observation of laser emission from a luminescent dye-doped cholesteric liquid crystal (CLC) excited by another dye-doped CLC laser. The idea is based on the cascade of two CLC cells containing two different dyes where the emission band of the first overlaps the absorption band of the second. This system of low threshold mirrorless lasers emphasizes the main advantages of these organic materials for lasing applications and identifies a simple laser device. Preliminary characterizations of these CLC laser systems produce evidence of remarkable features that suggest fascinating developments. The main aspects are related to the wavelength tunability of the laser emission and to the miniaturization of the device.