Sub-ppm gas phase Raman spectroscopy in an anti-resonant hollow core fiber

We demonstrate recent progress in the development of a Raman gas sensor using a single cladding ring anti-resonant hollow core micro-structured optical fiber (HC-ARF) and a low power pump source. The HC-ARF was designed specifically for low attenuation and wide bandwidth in the visible spectral region and provided low loss at both the pump wavelength (532 nm) and Stokes wavelengths up to a Raman shift of 5000 cm(-1). A novel selective core pressurization scheme was also implemented to further reduce the confinement loss, improving the Raman signal enhancement by a factor of 1.9 compared to a standard fiber filling scheme. By exploiting longer lengths of fiber, direct detection of both methane and hydrogen at concentrations of 5 and 10 ppm respectively is demonstrated and a noise equivalent limit-of-detection of 0.15 ppm is calculated for methane. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License.

Automated summary

This study demonstrates recent progress in the development of a Raman gas sensor using a single cladding ring anti-resonant hollow core micro-structured optical fiber and a low power pump source. The fiber provides low attenuation and wide bandwidth in the visible spectral region, and selective core pressurization scheme further enhances the Raman signal. Direct detection of methane and hydrogen at low concentrations is achieved by exploiting longer lengths of fiber.