High-sensitivty gas-phase detection using Raman Spectroscopy within a hollow-core microstructured optical fiber

High sensitivity gas-phase spectroscopy is vital for a range of applications including fuel production, storage, use, and safety in fusion reactors. Here, we report progress in developing a gas-phase sensing system based on stimulated Raman scattering with potential for low detection limits. Anti-resonant hollow-core fibers are filled with a gas sample, and the tight mode confinement and extended interaction length of the guided excitation laser with the sample is exploited to mitigate the low signal strengths associated with Raman spectroscopy by shifting from spontaneous to stimulated Raman scattering, thereby reducing the limit of detection. We present recent efforts by IS Instruments and Amentum to extend established continuous-wave spontaneous Raman scattering spectroscopy in anti-resonant hollow-core fiber developed at the University of Southampton. Then, using atmosphere as the medium for initial development, we demonstrate high gain for stimulated Raman scattering from N2 in both experiments and simulations. Furthermore, our simulations show that the weaker Raman signal from O2 can be detected separately from the N2 signal by injecting a seed at the Stokes wavelength corresponding to an O2 vibrational state, showing that signals ordinarily below the detection limit become detectable. This approach is a promising route towards separating trace amounts of hydrogen and its isotopologues in gas mixtures.