||For conventional lasers, light scattering is the most unwanted factor due to the reduction in lasing quality, while scattering is the key to developing random lasers. The feedback mechanism of random lasing is based on multiple scattering and interference effects in a chaotic amplifying medium. Such a laser possesses several unique and useful features, including multimode lasing, low spatial coherence, omnidirectional output, mirrorless cavity and simple fabrication process. Therefore, random lasers have enormous potential for applying to spackle-free imaging, lighting and optical communication devices. However, for typical random laser systems, including organic and inorganic media, it is hard to modulate the scattering domain size within one sample.|
Although blue phase liquid crystals exhibit optical isotropy on a macro scale, the discontinuity across the platelet boundaries still causes light scattering. This phenomenon can easily be observed when infusing a blue phase liquid crystal into a thick sandwich cell (d > 100 μm). Disordered platelet texture enables random lasing in liquid crystal blue phases, whose switchability and tunability of laser characteristics are reported in this thesis. The lasing action can be switched between coherent type and incoherent type by the thermal hysteresis effect. The randomness of lasing wavelengths can be determined by the platelet (domain) size, which can be set by controlling the cooling rate. After the blue phase scattering system is polymer-stabilized, coherent random lasing may occur in both the blue phase with an extended temperature interval and the isotropic liquid state; also, the selected modes are constant from one pulse to another. Additionally, if the laser dye is sensitive to temperature, the excitation threshold and the emission spectrum could be altered via thermal control.