Sensing methane in air with a mid-infrared frequency comb source

Summary form only given. We exploited a mid-infrared frequency comb source as a high brightness laser source for trace gas detection in air with different path lengths. The MIR frequency comb source (Menlo Systems, Mid-IR Comb) was based on difference frequency generation with fiber lasers [1]. We employed flip mirrors to reroute the mid-infrared beam for different path lengths, including a homebuilt multipass cell of ~584 m path length and open air paths of up to ~40 m. The transmission spectra were recorded with an optical spectrum analyser (Yokogawa, AQ6376).