Simultaneous trace detection of carbon monoxide and methane at 2.33 μm

The spectrum of a series of low concentration carbon monoxide and mixed gas (carbon monoxide, methane and nitrogen) was obtained around 2.33 μm using a tunable distributed feedback semiconductor laser with an astigmatic mirror multi-pass absorption cell (optical path length 100 m) at room temperature through direct absorption technique. The absorption lines of carbon monoxide at 4 288.289 8 cm-1 and methane at 4 287.650 15 cm-1 were chosen for trace detection. At the total pressure of 40 698 Pa, the detection limits of carbon monoxide and methane were gotten respectively, i.e. 8.15×10-6 for carbon monoxide (signal-to-noise ratio is about 216) and 18.48×10-6 for methane (signal-to-noise ratio is about 147).