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Title: Towards biomedical imaging with liquid crystal lasers
Author: Normand, Margaret Catherine
ISNI:       0000 0004 8508 8303
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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Lasers are important components in the advanced imaging techniques that have enabled rapid progress in biomedical research. Tunable wavelength lasers provide control of sample illumination, desirable for efficient fluorophore excitation, but are currently large and expensive. Liquid crystal (LC) lasers can be continuously tuned across the visible spectrum and, although not commercially available, can be fabricated cheaply. The aim of this thesis is to develop LC lasers for, and demonstrate their use in, biomedical imaging, thus providing evidence for their commercial potential. LC laser devices emit with much lower average power than is desirable for imaging. Two approaches to increasing the average power output were investigated, firstly using flowing LC droplets and secondly using a spinning LC cell. The spinning cell technique enabled emission at a pulse repetition rate of 10 kHz, with improved energy stability and acceptable wavelength stability. This is the highest repetition rate and highest average power (4.5mW) achieved with a LC laser to date. This result means that LC lasers can be considered for use in biomedical imaging and a broader range of applications. The LC laser could be operated for 2 hours at 10 kHz with less degradation in power than in static cell systems, indicating improved commercial viability. A stable emission wavelength, within ±2 nm, was demonstrated from a spinning cell with large, Grandjean domains. The quality of cells was therefore critical and large LC cells were required to maximise the benefits of the technique. Substrate surface flatness was found to be important in the fabrication of large, high quality cells. A portable spinning cell LC laser system was developed and integrated into a fluorescence microscope. The system was successfully used to capture fluorescence images of a fixed tissue sample, and was the first use of LC lasers as a light source for imaging. Multi-wavelength LC laser cells allowed convenient, arbitrary wavelength selection or rapid wavelength switching in a pre-defined sequence. The LC laser system was also found to be more affordable than competing tunable wavelength laser technologies. The flowing droplet approach was found to be a feasible method for achieving high repetition rate LC laser emission but did not result in suffcient intensity for imaging due to omnidirectional emission. Investigations into the effect of droplet shape on emission properties demonstrated a technique for manipulating laser light in microfluidic optical devices that could be used to enhance the sensitivity of LC droplet sensors.
Supervisor: Hands, Philip ; Underwood, Ian Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: liquid crystal lasers ; LC lasers ; spinning cell technique ; biomedical imaging ; stable emission wavelengths ; flowing droplet ; LC droplet sensors