Fast and sensitive wavelength modulation gas spectroscopy in micro-drilled hollow-core fiber

Micro-drilled anti-resonant fiber is demonstrated as a practicable tool for laser-based spectroscopic acetylene sensing, overcoming the slow fiber-filling time usually associated with hollow-core fiber-based methods. Microchannels were drilled through the side of the fiber, periodically along its length, using image processing to accurately target the gap between the capillaries for minimal loss. A 0.3% acetylene / 0.3% methane gas mixture balanced in air was tested in the near-infrared on two micro-machined fiber samples. Wavelength modulation spectroscopy was used to enhance the sensitivity of the detection. A 1 m anti-resonant fiber with microchannels every 5 cm was found to have a minimum detection limit of 380 parts per billion at atmospheric pressure and 100 s acquisition time with a 22 s fiber filling time without the use of a pressure differential. The filling time was 4.2 s for a 30 cm fiber with a closer microchannel separation of 2 cm.