Sensitivity limits of a tunable diode laser spectrometer, with application to the detection of NO(2) at the 100-ppt level.

A laser absorption spectrometer is described which uses a tunable diode laser and a 1-m multipass White cell to detect NO(2) 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 greater, similar 10(-7) m(-1), are examined.