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

Abstract

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.

Intercomparison of measurements of NO<sub>2</sub> concentrations in the atmosphere simulation chamber SAPHIR during the NO3Comp campaign

“…During the last decade cavity ring-down spectroscopy (CRDS) and its related forms cavity enhanced absorption spectroscopy (CEAS) and cavity attenuated phase shift spectroscopy (CAPS) have become powerful techniques to detect atmospheric trace gases (Ball and Jones, 2003;Brown, 2003) and have also been applied to NO 2 detection. A pulsed laser system , continuous wave laser diodes (Mazurenka et al, 2003;Kasyutich et al, 2003;Wada and Orr-Ewing, 2005;Kasyutich et al, 2006;Courtillot et al, 2006), light emitting diodes (LEDs) (Kebabian et al, 2005;Langridge et al, 2006;Gherman et al, 2008) and a xenon short-arc lamp (Venables et al, 2006) have been used as light sources.…”

Characterisation of the potential of frequency modulation and optical feedback locking for cavity-enhanced absorption spectroscopy

“…Fine adjustment of the distance and the phase of optical feedback were conducted by varying a voltage applied to the PZT- by means of a single voltage amplifier (SQV1/500, Piezomechanik). Laser radiation transmitted through the cavity mirror M2 was focused by means of an off-axis parabolic mirror An average mirror reflectivity of 99.97 % was estimated from the measurements of the ring-down time of the V-shaped cavity output (a cavity finesse F of ~10465) and compared to the phase-shift cavity ring-down spectroscopy measurements [18]. The cavity path length enhancement gain of 3333 and an effective absorption path length of 4133 m were obtained.…”

Stability of widely tuneable, continuous wave external-cavity quantum cascade laser for absorption spectroscopy

“…In most practical cases it is very useful to refer to the particular integration time corresponding to the minimum in the Allan variance plot [25,26]. This minimum describes the turn-over point where the ''white" noise with a slope of ''À1" in the logarithmic plot becomes dominated by the additional and undesired drift noise.…”

“…The Allan variance analysis was applied separately to the peak centre positions and also to the integrated absorbance areas. The variances were calculated for different numbers of successive scans (N) of the 200 recorded spectra using a program written in MathCad following an expression described elsewhere [14,26] for the strongest NO absorption peaks. The Allan variances of the peak centre positions are shown in Fig.…”