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.