Sensitivity limits of a tunable diode laser spectrometer, with application to the detection of NO_2 at the 100-ppt level

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Abstract
A laser absorption spectrometer is described which uses a tunable diode laser and a 1-m multipass White cell to detect NO2 in air with a sensitivity of better than 100 ppt. The modulation techniques employed to achieve this sensitivity are described in detail, and the noise mechanisms, which currently limit the detectable absorption coefficients to ≳10−7 m−1, are examined.