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Title: Metal photodissolution effect in As-S glasses and its application in IR grating fabrication
Author: Zakery, A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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This work investigates the feasibility of using the metal photodissolution effect peculiar to chalcogenide glasses as a means for producing grating structures for use at infrared wavelengths. The material properties and characteristics of the effect relevant to grating fabrication and performance has been examined, the study dealing exclusively with Ag photodissolution in As-S glasses. Different fabrication techniques have been investigated and the performance of the gratings produced has been compared with theoretical predictions. A technique based on simultaneous reflectivity and transmissivity measurements has been developed and used to probe the kinetics of photodissolution, in particular its dependence on wavelength and intensity of illumination. A composition around As30S70 was found to be optimum for applications since it had maximum sensitivity and also exhibited negligible photodarkening. A model has also been proposed for photodissolution which explains the spectral dependence and the intensity dependence of the photodissolution rate and suggests that the actinic radiation is absorbed in the photodoped layer. Gratings were produced both holographically and by mask exposure and suitable etchants identified for removal of the undoped material and the residual Ag layer. A coupled-wave model has been developed which predicts that diffraction efficiencies of up to 90% can be achieved in the multiwave regime at 10.6 μm. Diffraction efficiencies of up to 20% have been measured for both the zero and ± 1 orders at 632.8 nm which are in good agreement with the results of the theoretical model. Optical constants of both the undoped and Ag-doped As-S films have been measured over the wavelength range 0.5-12 μm to enable the analysis of kinetics measurements and also the development of the theoretical model. The results of these measurements show that there is a significant change in the refractive index (by up to 0.5, depending on Ag content) and also in the optical gap of the As-S films upon incorporation of silver, although the absorption coefficient of the Ag-doped As-S films remains small in the IR. The results of a secondary ion mass spectroscopy analysis showed that the composition of the As-S films varies very little with depth while the silver concentration may vary by up to 20% in the Ag-doped As-S films.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available