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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.

The use of optics in the fields of nano-technology, telecommunication and medicine has been growing exponentially in recent years. Application of liquid crystals within optics has been a growing trend from flat screen displays to variable focus lenses in a digital versatile discs. One area of the recent developments within optics has been the development of two-photon fluorescence microscopy and high-density three-dimensional optical data storage. In such applications, where a light beam has to be focused deep within the volume of bulk media, aberrations are introduced. The most dominant aberration is spherical aberration which results from the mismatch in refractive indices of the immersion and recording media. The aim of this thesis is to design a liquid crystal lens for dynamic tube length compensation of the spherical aberration. Liquid crystal phase plates are used in everyday liquid crystal displays (LCDs) such as mobile phones and calculators. The technologies required to manufacture a liquid crystal phase plate are well understood. However, an application like three-dimensional data storage requires different properties in the liquid crystal phase plate, which are investigated in this thesis. To fabricate our liquid crystal phase plate we used ZLI-5049-000 from MERCK as the liquid crystal medium, with poly-vinyl alcohol (PVA) and Indium Tin Oxide (ITO) providing the insulating and conducting layers, respectively. It has been demonstrated that vacuum vapour deposition can be used to coat a glass substrate with ITO. However, in order for the ITO coating to be conductive a method is developed where the substrate is heated to 300oC before, during and after the coating. Similarly, a method has been developed for producing a uniform 10 μm coating of PVA on top of the ITO. In order to produce a liquid crystal lens with the properties required to compensate for spherical aberration an investigation into the properties of the liquid crystals is first conducted. A liquid crystal phase plate described in chapter 3 is characterised to determine the effect of the rubbing direction of the insulating layer and the effective refractive index change with applied voltage. It has been demonstrated that an effective change in refractive index of 0.11 can be achieved with 30 volts applied across the ITO electrodes. Based on the characterisation of the liquid crystal phase plate four different liquid crystal lens designs have been proposed and tested. The lens designs are based upon convergent and divergent lenses with different refractive index lens substrates. It is determined that a liquid crystal lens with a divergent lens substrate with a refractive index of 1.785 can be used to effectively compensate for spherical aberration. This has been confirmed experimentally by using the liquid crystal lens in a two-photon confocal microscope and measuring a increase in detected intensity at a depth below the surface of a sample. The research conducted in this thesis shows the ability to dynamically compensate for spherical aberration introduced by a mismatch in the refractive indices between the immersion and sample mediums. It has also been demonstrated that new methods for fabricating the conductive and insulating layers are suitable for producing a liquid crystal lens. A liquid crystal lens based on the research in this thesis could be used in three-dimensional data storage or microscopy applications.