MQW laser diode photoacoustic detection of formaldehyde in 2.3 μm spectral range

The spectrum of formaldehyde was studied in the 4350 - 4361 cm-1 region using photoacoustic detection in combination with a semiconductor GalnAsSb/AlGaAsSb diode laser as a radiation source. This laser operates at laboratory and higher temperatures in the 4342 - 4362 cm-1 region with an output of about 1 mW. The spectrum of formaldehyde was measured photoacoustically and this was compared with other techniques, such as laser absorption in a single path 0.4 m long cell and Fourier transform spectroscopy. The dependence of the photoacoustic signal on the pressure of the measured gas was recorded. The same technique was employed to determine the detection limit (less than 0.1 ppmV) of formaldehyde diluted with nitrogen for the strongest absorption line in the emission region of the diode laser.