Vasili L. Kasyutich

Phase-shift off-axis cavity-enhanced absorption detector of nitrogen dioxide

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.

In situ vehicle engine exhaust measurements of nitric oxide with a thermoelectrically cooled, cw DFB quantum cascade laser

This paper describes the application of a thermoelectrically cooled, continuous wave (cw), single mode distributed feedback (DFB) quantum cascade laser (QCL) to the real-time, in situ vehicle engine exhaust monitoring of nitric oxide. Experiments have been carried out on a static gasoline engine test bed where the engine operating conditions can be varied in a controlled manner. Results show the response of the nitric oxide concentration to engine conditions. The prospects for further multispecies in situ measurements are discussed.