HIGH-SENSITIVITY DETECTION OF NO2 USING A 740 NM SEMICONDUCTOR DIODE-LASER

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