Nanofiber enhanced stimulated Raman spectroscopy for ultra-fast, ultra-sensitive hydrogen detection with ultra-wide dynamic range

The increasing importance of hydrogen as an energy carrier and industrial material calls for hydrogen sensors with higher sensitivity, better selectivity, faster response, and wider dynamic range. Here, we report a nanofiber (NF) sensor that satisfies these requirements with a single sensing element. The sensor is based on stimulated Raman scattering spectroscopy, but the tightly confined evanescent field associated with the NF enhances the Raman gain per unit length by a factor of 30 to 102 over the state-of-the-art hollow-core photonic crystal fibers and more than 104 over free-space beams. The NF has excellent mode quality, which ensures mode-noise-free measurement and maximizes the signal-to-noise ratio. An experiment with a 700-nm-diameter, 48-mm-long silica NF operating in the telecom wavelength band demonstrates hydrogen detection from a few parts per million to 100% with a response time less than 10 s. The sensor would be useful for a range of applications, including detection of hydrogen leakage as well as monitoring of battery charging, fuel cells, and electric power transformer health conditions. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement