Laser photo-acoustic detection of nitrogen oxide

Abstract

The absorption property of NO in the wavelength region of 420-470nm is surveyed by the technique of photo-acoustic (PA) spectroscopy. It is found that NO molecule is excited though multi-photon process. The optimum excitation wavelength in this region is decided when one detect NO with PA technique. It is 452.4nm or 429.6nm which corresponding to the transition of NO A 2 Σ(v'=0,1)←X 2 Π (v=0). The variation of PA signal versus buffer gas pressure and NO concentration is measured. It is shown that owing to the enhancement of V-T transfer energy with buffer gas pressure, the intensity of the PA signal increases when the pressure of the buffer gas is increased. But the PA signal is almost invariable when the buffer gas pressure is more than 5.32×10 4 Pa. The PA signal shows itself as linearity variation with NO concentration. Under the condition of standard atmosphere, a detection limit of 5ppm is obtained on the basis of SNR=1 with a homemade apparatus.