VUV laser-induced plasma spectroscopy for low level sulphur detection in steel
O'Leary, Eoin P. (2007) VUV laser-induced plasma spectroscopy for low level sulphur detection in steel. PhD thesis, Dublin City University.
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When a short, high energy pulse of laser light is focused onto a solid target a high density, high temperature plasma is formed. This plasma emits radiation across a wide spectral range, from the x-ray to the infra-red. In this thesis, a variant of the well-established spectroscopic technique known as Laser-Induced Plasma Spectroscopy (LIPS) is used in order to more sensitively quantify sulphur content in steels. LlPS is a well-established method for both quantitative and qualitative analysls of solids, liqurds and gases A particular problem exists with the elemental characterisation of the light elements (2 < 20) including sulphur in that the strongest resonant emission lines from these elements lie in the VUV part of the spectrum.
In this thesis, the VUV region of the spectrum has been exploited using a spatially-resolved approach which has proved to be superior to the more conventional time-resolved ultraviolet and visible LlPS experiments Spectral surveys of the VUV region have been conducted in order to isolate interference-free sulphur emission lines A number of optimisation studies have been made in order to improve the signal to standard deviation ratro in the characteristic background continuum emission. These included modification of the laser pulse energy, power density, lens focuslng type (cylindrical and spherrcal) and ambient gas type & pressure.
As a result of these experiments, optimum conditions in which to construct callbration curves were found. Steel targets of certified sulphur concentration in the range 27 - 3800 pprn were used in the construction of these calibration functions. The sensitivrty of the LlPS technique has been improved on substantially with an ultimate detection limit of 1.7 +- 0.1 ppm achieved using the emission features of the S V emission line at 78.65 nm.
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