For the last 20 years, there has been considerable interest in chiral nematic liquid crystal band edge lasers. The birefringent molecules of chiral nematic liquid crystals form a periodic helical structure, which results in a photonic bandgap for circularly polarised light with the same sense of rotation as the helix. A large increase in effective gain is seen for a fluorescent gain medium within the liquid crystal at the band edges, resulting in lasing. Applications of liquid crystal lasers could include miniature medical diagnostic tools, large-area holographic laser displays, and environmental sensing. The wavelength of emission from dye-doped chiral nematic liquid crystals is highly flexible, with lasers demonstrated across the visible range and near infra-red. This thesis investigates two routes for improving the functionality of chiral nematic liquid crystal lasers, supported by mathematical modelling of expected lasing wavelengths based on reflection and transmission by anisotropic layers. Perovskite is tested as a replacement for fluorescent laser dyes as a gain medium,both in the form of quantum dots dispersed in liquid crystal, and as films placed in liquid crystal structures. It is shown that while the perovskite tested provides some emission, it is not compatible for lasing in these devices, and suggestions for building on these results are made. In-plane switching is tested and developed as a means to achieve tuning of the laser wavelength, demonstrating a continuous wavelength shift of 15 nm, from 600.71 nm to 585.03 nm, over a voltage range of 100 V. This is an improvement on previous tuning in related devices, and may be extended with optimisation of cell thickness,electrode geometry, and initial lasing wavelength. Accurate descriptions of the refractive index profile of the liquid crystal and perovskite are developed and included in mathematical modelling, in addition to descriptions of the wavelength-dependent gain of a laser dye and perovskite. Suggestions for developing this modelling are made, particularly by the inclusion of accurate modelling of the distortion caused by in-plane switching.

In this study, we study three kinds of surface treatments in the blue phase lasers. Three kinds of surface treatments include no surface treatment, homogeneous alignment ,HA, and vertical alignment ,VA. Blue Phase liquid crystal is a three-dimensional photonic crystal, and it can be used to be a laser cavity. When the blue phase doped with a laser dye, a laser emission can be observed under appropriate pumping energy. In the first part, we fabricate the blue phase lasers with three kinds of surface, there are different surface treatments to study the surface effect of the optoelectronic properties. It is found that the threshold pumping power is significantly decreased under a surface treatment on glass substrate. In the second part, we change cooling rate in the formation of the blue phase liquid crystals, and study the optoelectronic properties of blue phase lasers. The experiment results reveal that the slower cooling rate leads to a order blue phase substrate, resulting in a lower threshold pumping energy of the blue phase laser.