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

A trace gas absorption sensor for formaldehyde (H2CO) 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 in its v1 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 H2CO measurements at 1 Hz sampling rate. The AllanWerle deviation plot reveals that a minimum detection limit of ~1.5 ppbv can be achieved for an averaging time of 140 seconds.