Hydrogen Detection by Coherent Anti-Stokes Raman Spectroscopy with a Raman Shifter Cell

This contribution presents hydrogen detection by coherent anti-Stokes Raman spectroscopy using a single nanosecond pulsed Nd:YAG laser and a Raman shifter cell. The frequency-doubled Nd:YAG laser beam at 532 nm is used to pump a Raman shifter cell filled with hydrogen to generate the Stokes beam at 683 nm. The beams are combined and focused in the detection cell filled with hydrogen diluted in nitrogen to generate the anti-Stokes beam that is collected and analyzed to infer the hydrogen number density. The parameters of the Raman shifter cell, mainly the laser seeding, cell pressure, and input energy, are optimized in order to maximize the detected signal. The optimum conditions were determined to be a seeded pump beam with a pressure slightly below atmospheric pressure. The optimized Raman cell was used to generate a Stokes beam for coherent anti-Stokes Raman spectroscopy in second cell filled with varying concentrations of hydrogen. Hydrogen is then detected in atmospheric pressure mixtures with nitrogen where the hydrogen concentration is diluted down to ~100 part-per-million (ppm) molar concentration.