Abstract
A near-infrared NH3 sensor based on a 1512 nm distributed feedback (DFB) laser was designed to perform real-time and online detection of NH3 in the industrial denitrification. A miniaturized multi-pass gas cell (MPGC) is utilized as a site for infrared laser-gas interaction, in which the infrared light is reflected back and forth 76 times within the MPGC, with an effective optical path length of 20 m. High-precision concentration inversion of the detected second harmonic (2f) signals at both high and low concentrations was performed by the particle swarm optimization-least squares support vector machine (PSO-LSSVM) algorithm, and the linear correlation coefficient R2 between the standard and measured concentrations could be as high as 0.9999 or later in both cases. The sensor was tested for stability for 1 h and its Allan -Werle deviation was analyzed. The minimum limit of detection (LoD) of the sensor is 3.95 ppb at an averaging time of 38 s. An outdoors deployment of the sensor was reported for detection of the leaking NH3 in Laboratory Building.
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