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

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 similar to 580 m path length, and achieved the sensitivity about 7.6 x 10(-7) cm(-1) with 80 ms data acquisition time. We determined the methane concentration as similar to 1.5 ppmv in the ambient air of the laboratory, and the detection limit as similar to 60 ppbv for the current setup.