Interband cascade laser based absorption sensor for ppb-level formaldehyde detection

摘要

A trace gas absorption sensor for formaldehyde (H_2CO) detection was developed using a continuous wave, room temperature, low-power consumption interband cascade laser (ICL) at 3.6 μm. The recent availability of ICLs with wavelength ranged between 3-4 μm enables the sensitive detection of trace gases such as formaldehyde that possesses a strong absorption band in this particular wavelength region. This absorption sensor detected a strong formaldehyde line at 2778.5 cm~(-1) in its v_1 fundamental band. Wavelength modulation spectroscopy with second harmonic detection (WMS-2f) combined with a compact and novel multipass gas cell (7.6 cm physical length, 32 ml sampling volume, and 3.7 m optical path length) was utilized to achieve a sensitivity of ～6 ppbv for H_2CO measurements at 1 Hz sampling rate. The Allan-Werle deviation plot reveals that a minimum detection limit of ～1.5 ppbv can be achieved for an averaging time of 140 seconds.