MOTIVATION
Optical, non-intrusive diagnostic methods such as Raman spectroscopy offer the advantage of providing spatially and temporally resolved information about processes through the interaction of light and matter without disturbing them. For example, the chemical composition and temperature in the sample volume can be measured. This only requires optical access to couple the laser in and the measurement signal out. However, one challenge is to reduce the partially broadband background, which is caused by thermal radiation or unwanted laser-induced fluorescence in high-temperature processes, for example. This otherwise overlays the weak Raman signal and makes quantification difficult or impossible.
METHOD
Shifted-excitation Raman difference spectroscopy (SERDS) offers a promising approach to quantitatively investigate and analyse Raman measurements in highly background-polluted gas phase flows. In this approach, two Raman spectra are recorded with slightly shifted excitation wavelengths. This utilises the fact that the background, for example due to thermal radiation or laser-induced fluorescence, remains comparatively constant at slightly different excitation wavelengths and only the Raman signal shifts in the spectral direction. By forming a difference spectrum from the two Raman spectra, it is then ideally possible to completely eliminate the background. The research question is to extend the approach to processes in the gas phase in the vicinity of solid surfaces, which has so far remained unexplored for spatially/temporally resolved 1D-SERDS.
