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Title: Dye doped liquid crystal lasers
Author: Gillespie, C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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This thesis examines the emission properties of dye-doped liquid crystal lasers, which are of interest because they have the potential to provide compact, low threshold, tunable laser sources for applications ranging from medicine to displays. The primary aim is to provide the first detailed study of the interactions between liquid crystals (LCs) and laser dyes and to examine their effect upon the emission properties of dye-doped liquid crystal lasers. Five different dyes are examined and, in all cases, the LC host (a nematic mixture, E49) is shown to have a significant effect upon the properties of the dye, through a combination of general and specific solvent-solute interactions. Lasing is demonstrated from all five dyes in the chiral nematic (N*) mesophase. Conventional xanthene laser dyes, rhodamine 6G chloride and rhodamine B chloride, are shown to be unsuitable for N*LC lasers because their ionic nature and isotropic molecular shapes limit their solubility in LC materials. Emission is shown to occur preferentially at the long wavelength reflection band edge for small degrees of alignment of the dye in the LC host. Three elongated laser dyes (DCM, PM597 and PM580) are shown to be more compatible with E49. N*LC laser samples were made using dye concentrations in the range 0.5 wt% to 2.0 wt%. For each dye, slope efficiency (ηs) values were used to calculate relative quantum efficiency values, which decreased linearly as the concentration increased. ηs is shown to peak at a characteristic value corresponding to the balance between increasing absorbance and decreasing quantum efficiency with increasing dye concentration. The largest ηs demonstrated is 32%, which corresponds to 1.0 wt% PM597. The Eth of both PM597 and PM580 is shown to increase linearly with increasing concentration, whereas the Eth of DCM shows the opposite tendency. It is proposed that the different Eth trends indicate different quantum efficiency quenching mechanisms. Lasing was demonstrated from novel bimesogenic mixtures that showed wide temperature range blue phase I* (BP I*) mesophases. The preparation and properties of the BP I* samples are described. the nature of the laser emission is shown to depend upon the input energy used. For low inputs energies (<~ 3μJ/pulse), multimode lasing is demonstrated from the BP I* texture, whereas for high input energies (> ~ 3 μJ/pulse) random lasing is demonstrated from optically induced focal conic (N*) textures in the BP I* samples.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available