Long-path monitoring of NO_2 with a 635 nm diode laser using frequency-modulation spectroscopy

Abstract

In situ monitoring of traffic-generated nitrogen dioxide (NO 2 ) emissions using long-path absorption spectroscopy is reported. High-sensitivity detection of NO 2 is achieved by employing two-tone frequencymodulation spectroscopy at a visible absorption band using a tunable high-power diode laser operated around 635 nm. A real-time absorption spectrometer is accomplished by repetitively applying a rectangular current pulse to the diode-laser operating current, allowing detection of isolated NO 2 absorption lines. A detection limit of 10 g͞m 3 for NO 2 at atmospheric pressure using a 160 m absorption path is demonstrated. Continuous monitoring of NO 2 over a road intersection at peak traffic is performed.

Combined optical porosimetry and gas absorption spectroscopy in gas-filled porous media using diode-laser-based frequency domain photon migration

“…We should note that the refractive index only affects the optical properties but not the MOPL, since we use the same refractive index to calculate MOPL in Eqs. 3and (4). An extended application of the combined FDPM and GASMAS method is to provide information on the refractive index of the scattering medium (bulk material), i.e., sm n , which is important for understanding its optical properties [46].…”

“…Tunable diode laser absorption spectroscopy (TDLAS) has been widely used for selective and sensitive gas detection in a multitude of contexts, e.g., combustion diagnostics [1,2], atmospheric trace gas monitoring [3,4], and biomedical applications such as human breath monitoring [5,6]. A review paper regarding the application of the TDLAS technique can be found in [7].…”

A New Laser Based Approach for Measuring Atmospheric Greenhouse Gases

“…Although several other open path techniques exist [7][8][9][10][11][12][13][14], LAnTeRN is a different implementation which simultaneously transmits and receives both the on and the offline wavelengths. This key difference makes many of the noise sources including scintillation common to both wavelengths and since this is a ratiometric measurement they cancel in the ratio.…”

Detection of nitrogen dioxide using an external modulation diode laser

“…Various approaches have been used to detect concentrations of NO 2 . Conventional NO 2 measurement techniques include chemical analysis [3], differential optical absorption spectroscopy [4][5][6][7][8], broadband absorption spectroscopy [9][10][11][12], and tunable diode laser absorption spectroscopy [13]. These approaches have been widely noted and could achieve high sensitivity.…”