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Sensitive harmonic detection of ammonia trace using a compact photoacoustic resonator at double-pass configuration and a wavelength-modulated distributed feedback diode laser

: Lima, Guilherme; Mota, Leonardo; Miklós, András; Angster, Judit; Dubovski, Zlatko; Silva, Marcelo da; Sthel, Marcelo; Vargas, Helion


Applied Physics. B 117 (2014), No.1, pp.333-341
ISSN: 0340-3793
ISSN: 0721-7269
ISSN: 0946-2171
ISSN: 1432-0649
Journal Article
Fraunhofer IBP ()

A sensitive detection of ammonia in parts per billion by volume is described. The system based on photoacoustic spectroscopy (PAS) consists of distributed feedback laser diode emitting near 1,531.7 nm and a compact PA cell at double-pass configuration. In order to optimize the signal background ratio of the system, two types of modulations were tested, amplitude and wavelength modulations (WM). Using a digital lock-in amplifier, the 1f and 2f detection in WM could be investigated. A detection limit of 470 parts per million by volume could be achieved at WM-2f. In the sense of quantifing the adsorption–desorption process, the response time of the system and detection accuracy was performed in different flows. Response times between 10 and 49 s, depending on the flow rate, were obtained which enables the PA system to measure low concentrations of ammonia with high accuracy in real time.