A novel type of fiber-optic cavity sensor for hydrogen diffusion into and out of fibers is presented. The sensor is an implementation of a cavity ringdown scheme in a silica-based single-mode fiber that has been exposed to gaseous hydrogen at normal pressure. The measured ringdown times during the H_(2) diffusion show good agreement with a theoretical diffusion model. This model allows the determination of the diffusion coefficient of hydrogen in silica, resulting in D=(3.02±0.07)×10~(-15) m~(2)/s at 30℃.
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