Development of Spectroscopic Measurements for Raman and Thomson Scattering Diagnostics ——Applications in Combustion and Plasma

Abstract: This thesis work concerns methods for improved spectroscopy including stray-light suppression, dynamic range improvement and signal enhancement. These methods were applied in Raman and Thomson- scattering spectroscopy in combustion and plasma. First, the stray-light suppression method Periodic Shadowing (PS) is implemented in an experimental setup with a high-power high repetition rate laser system used for Raman measurements in premixed, laminar, flat flames. It is shown that the background is reduced by a factor of 10 or more. Weak spectral lines can be distinguished and therefore better molecular species identification, concentration and temperature evaluation were performed. Second, initial test for Thomson scattering measurements in a gas discharge plasma was carried out with the experimental setup. Third, the method of using a Digital Micro-mirror Device (DMD) is combined with the PS method to boost the dynamic range in spectroscopic imaging. A novel DMD-PS spectrometer was designed and built and shows significantly enhanced performance, improving the dynamic range by a factor of at least 50. Such a high-dynamic-range and stray-light-reduced spectrometer has potential to be implemented in future imaging spectroscopy.