Mid-infrared dual frequency comb spectroscopy based on fiber lasers for the detection of methane in ambient air

Abstract

We utilize mid-infrared dual frequency comb spectroscopy for the detection of methane in ambient air. Two mid-infrared frequency comb sources based on femtosecond Er:fiber oscillators are produced through difference frequency generation with periodically poled MgO-doped lithium niobate crystals and stabilized at slightly different repetition rates at about 250 MHz. We performed dual frequency comb spectroscopy in the spectral range between 2900 cm−1 and 3150 cm−1 with 0.07 cm−1 resolution using a multipass cell of ~580 m path length, and achieved the sensitivity about 7.6 × 10−7 cm−1 with 80 ms data acquisition time. We determined the methane concentration as ~1.5 ppmv in the ambient air of the laboratory, and the detection limit as ~60 ppbv for the current setup.