High-sensitivity detection of NO2 using a 740 nm semiconductor diode laser
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An AlGaAs diode laser was used to detect NO2 absorption lines belonging to the (0 0 0)–(2 13 1) vibrational band, within the X˜2A1 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 μbar 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 N2 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.
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