A practical-use hydrogen gas leak detector using CARS

The purpose of this research is to develop a non-contact, fast response, practical-use hydrogen gas leak detector using Coherent Anti-Stokes Raman Spectroscopy (CARS). To make it realize, the optimization of its practical light source was investigated minutely for this detector. The light source condition to generate the highest Anti-Stokes Raman light is obvious on the theory, while it is not matched with its practical condition under the physical constraints. In this study, the light source configuration was devised in which the laser beam (355 nm) is split into two optical paths and the Raman cell filled hydrogen gas is arranged on the one side. As a result, it was found that when its irradiation ratio (R = Stokes light/Pump light) was 0.140 ≤ R ≤ 0.173, the generation efficiency of the anti-Stokes light was high. The high generation efficiency of anti-Stokes light can be maintained even if the laser light intensity and hydrogen pressure to the Raman cell are changed. We discussed the difference between the obtained experimental results and the theoretical results. The detection limit of hydrogen gas concentration of our detector was set to 500 ppm. As a result, hydrogen gas up to 200 ppm ± 15% (lower detection limit: 157 ppm) could be measured. In addition, the measurement value of the hydrogen gas leaking from a nozzle was considered under the acceptance situation, too.