An intensified ultra-high-speed optical emission spectroscopy system for hypersonic impulse test facilities

This paper provides a comprehensive investigation into creating a spectroscopy system capable of capturing quantitative data that are spatially, spectrally, and temporally resolved, at a minimum of 100 kHz frame rate using an ultra-high-speed camera, a high-speed image intensifier, and a spectrograph. The system was thoroughly tested in a controlled environment using a PhatLight green LED and a Labsphere CSTM-USS400-HI calibration lamp to determine its capabilities and limitations. The sensitivity at different wavelengths and how exposure time and intensifier gain settings affect the sensitivity of the system were evaluated. The system performed well with an exception of a drop in intensity when recording over long periods of time. Upon investigation, it was discovered that the intensifier cannot sustain a constant gain at higher counts for extended lengths of time. The gain drop in the intensifier is minimal for test times less than 200 \(\mu\)s, allowing the system to be operated on short-duration facilities. For test times of milliseconds, the gain drop must be accounted for either in data calibration or analysis. The system proved successful in capturing spectral data at a 100-kHz frame rate on the University of Queensland’s X2 free-piston driven expansion tube, when investigating contamination in the facility. The ultra-high-speed intensified optical emission spectroscopy system allowed for spectral data that were spatially, spectrally, and temporally resolved in a short-duration hypersonic impulse testing facility, giving a better understanding of interactions and phenomena occurring in radiating flow.