Phase-sensitive, off-axis cavity-enhanced absorption spectroscopy techniques with a rectangular pulse current modulated violet diode laser (∼404 nm) were applied to measurement of nitrogen dioxide (NO2) in diluted standard mixture and laboratory air. An optical cell of an NO2 detector was bounded by two plano-concave mirrors with a diameter of 7.75 mm and a reflectivity of 0.999, separated by a distance of 43 cm. The phase shift measurements due to Rayleigh scattering extinction were used for calibration of the detector. NO2 sensitivities were extracted from synchronous measurements of either the cavity output light intensity or the phase shift induced by the cavity. NO2 noise equivalent detection limit (S/N = 1) of 1–2 ppbv was demonstrated for the intensity measurements with a lock-in amplifier time constant of 1 s. From the Allan plot of the intensity measurements the NO2 minimum concentration was estimated to be 0.24 ppbv in 80 s at atmospheric pressure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.