Visible acousto optic tunable filter hyperspectral imaging for inductively coupled plasma optical emission spectrometry
Carnahan, Jon W.||Duffin, Kirk L.
Ph.D. (Doctor of Philosophy)
Department of Chemistry and Biochemistry
Inductively coupled plasma spectrometry; Acoustooptical devices; Tunable filters
Inductively coupled plasma optical emission spectrometry (ICP-OES) is widely used in trace-metal analysis. However, the behavior of this hot, ionized gas and effects on analyte excitation and ionization are not fully understood. To obtain sufficient information, two previous approaches, Abel inversion and tomography, have been used. The significant drawbacks of these approaches include complex optical and data manipulation systems, the significant amounts of time required for data collection, and long-term plasma drift and flicker. A much more ideal approach would be to obtain multiple instantaneous high-spectral resolution images of the entire discharge while retaining a fast speed of wavelength access across a broad spectral range. An acousto-optic tunable filter hyperspectral imaging (AOTF-HSI) system meets all of these plasma imaging requirements. An AOTF is a digitally accessible, compact, variable-wavelength optical filter that operates based on the interaction between optical radiation and a shear wave traversing an anisotropic material. A hyperspectral imaging (HSI) system is constructed by combining an AOTF and a monochrome CCD camera. The initial characterization indicated that the AOTF performed according to the theoretical equations for the frequency/wavelength relationship and bandpass as a function of wavelength. The system spatial resolution was achieved 8.8 μm horizontally and 12.4 μm vertically with 1:1 imaging optics. Test images varied from a red-green-blue (RGB) target, to a stamp, to a fluorescein-injected bovine eye. For AOTF-HSI applications of ICP-OES, nine elements, Al, Ba, Ca, Ce, Cr, Li, Mg, Na, and Sr, were studied. Using in-house developed software, spectral information was acquired at each pixel within the image. Background (continuum) corrected images were obtained. Vertical profiles of Sr atom and ion emission are described as an example to demonstrate the capability of AOTF-HSI on plasma imaging. Plasma chemistry for these elements was studied through variation of the ICP rf power, nebulizer sample carrier gas flow rate, liquid sample delivery rate, etc. Results indicate that correlations between elements' excitation and ionization energies and the enhancements on emission intensities could be clearly discerned. Finally, a Cr and Mg mixture solution was used to demonstrate the multielement analysis capabilities of the AOTF-HSI system.
Bei, Ling, "Visible acousto-optic tunable filter hyperspectral imaging for inductively coupled plasma optical emission spectrometry" (2004). Graduate Research Theses & Dissertations. 6658.
xvi, 149 pages (some color pages)
Northern Illinois University
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