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Title: COMAS development for concentration probing of gas phase discharge systems
Author: Hatcher, M. G.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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The work presented in this thesis describes the further development of the pump-probe laser spectroscopic technique known as Concentration-Modulated Absorption Spectroscopy (COMAS), concentrating on its use as an analytical tool for the investigation of various atomic systems. The systems analysed here include a direct current glow discharge with a lithium cathode, and a neon hollow cathode discharge lamp. The COMAS method necessitates the use of a Lock-In Amplifier (LIA) for signal derivation and output measurement. A substantial feature of the work presented here is concerned with the way in which COMAS signals are affected by phasing effects, and Chapter 2 concentrates on the relationship between COMAS signal generation and LIA measurement of that signal. Meaningful, quantitative analysis using COMAS generally requires the use of an accompanying absorbance measurement of the sample in question, and the development of COMAS has in fact been limited by the quality of such absorbance measurements. This problem is addressed in Chapter 3, which describes the investigation of two novel absorption techniques with a view to future use in conjunction with COMAS. With the theoretical and experimental basis to COMAS fully described in Chapter 4, the technique is subsequently used to probe the distribution of sputtered Li atoms in d.c. glow discharge for a variety of conditions. The results allow determination of the first experimentally derived values of thermalisation cross-sections in the gas phase, and provide valuable data for glow discharge modelling. In the final three chapters, the COMAS technique is significantly extended to incorporate analysis of dynamic 3-level systems. This development is approached theoretically in Chapter 6, and shows that certain extra parameters which affect COMAS signals require determination. The 3-level theoretical treatment is tested experimentally in Chapters 7 and 8 by investigation of a neon hollow cathode discharge, with the atomic neon electronic scheme providing an analogous 3-level system. The phase behaviour of the cw COMAS neon signals is briefly investigated in Chapter 8a.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available