Dual-track spectrometer design for 1D gas-phase Raman spectroscopy

Abstract

In this study, a new design for a 1D gas-phase Raman spectrometer is presented, utilizing two dedicated tracks to image different properties of the measured signal onto a single charge-coupled device (CCD) chip. Two possible configurations are shown: a polarization-separation configuration, which separates the detected Raman signal into s- and p-polarized shares; and a dual-resolution configuration, which captures all process-relevant species in a range of approximately 515-4650 cm−1 on one track and the highly resolved nitrogen spectrum on the other. This new spectrometer design offers several advantages when compared to traditional polarization-separation/dual-resolution systems, which often use switchable filters or two different spectrometers in tandem to achieve comparable measurements. Employing only one camera eliminates signal drift and minimizes calibration as well as spatial/spectral mapping issues. To validate instrument performance, the detection was paired with a continuous wave (CW) excitation system and used to measure in two generic but diagnostically challenging flow scenarios: flow near a heated surface, where thermal radiation is significant addressed by the polarization-separation configuration of the spectrometer and a channel flow at moderate temperatures in confined space, where the dual-resolution configuration of the spectrometer was employed. The results for both configurations and experiments showcase the instrument’s ability to effectively suppress background radiation (polarization-separation) or measure local gas-phase temperatures with higher accuracy (dual-resolution) and are complemented with resolution measurements yielding a maximum spatial resolution of 21.9 lp/mm along the 1D probe volume.