High-sensitivity detection of NO2 using a 740 nm semiconductor diode laser

An AlGaAs diode laser was used to detect NO2 absorption lines belonging to the (000)-(2131) vibrational band, within the (X) over tilde(2) A(1) electronic ground state, at 739 nm. A simple absorption spectrometer based on wavelength-modulation spectroscopy with second-harmonic detection was developed. The minimum detectable pressure of pure NO2 was 0.1 mu bar with 2 m absorption path-length, corresponding to an absorbance of 10(-6). High-sensitivity detection of NO2 was also performed in the presence of N-2 and air at different total pressures: The effects on the detection limit of our apparatus were accurately investigated. The minimum NO2 concentration at 500 mbar of air was measured to be 2 ppm.