Comparison of Three Compact Raman Systems with Excitation Laser Wavelengths of 405, 532, and 660 nm (µRA-RGB)

Based on good experience with Raman systems in general and the µRA systems in particular, we try to expand the capabilities and possible applications of Raman spectroscopy. A central aspect is the excitation wavelength since signal intensity and fluorescence background depend on that. Besides the common 532-nm laser (green), we used a 660-nm (red) and 405-nm (blue) laser, hence the name µRA-RGB. All three systems share the same basic principle (fiber coupling between laser, Raman head, and spectrometer) and only differ because of necessary adjustments for the excitation wavelength used, like the laser edge filter. As the original µRA system has already proved its capability to simultaneously detect all six hydrogen isotopologues, this first RGB study was limited to H₂, D₂, and equilibrated mixtures of both. With one of Tritium Laboratory Karlsruhe’s proven LARA systems connected to the same gas mixing loop system, comparing the µRA systems against it was possible. This paper shows the results of the measurement campaign comparing all three µRA systems (405-, 532-, 660-nm excitation wavelengths) and the comparison to the well-established large Raman systems (LARA, 532 nm).