Widely-tunable mid-infrared fiber-coupled quartz-enhanced photoacoustic sensor for environmental monitoring

• Published in: Optics express Vol. 22; no. 23; pp. 28222 - 28231
• Main Authors: Siciliani de Cumis, M, Viciani, S, Borri, S, Patimisco, P, Sampaolo, A, Scamarcio, G, De Natale, P, D'Amato, F, Spagnolo, V
• Format: Journal Article
• Language: English
• Published: United States 17.11.2014
• Subjects: Environmental Monitoring - instrumentation; Equipment Design; Gases - analysis; Lasers, Semiconductor; Quartz; Spectrum Analysis - instrumentation
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.22.028222

A compact widely-tunable fiber-coupled sensor for trace gas detection of hydrogen sulfide (H₂S) in the mid infrared is reported. The sensor is based on an external-cavity quantum cascade laser (EC-QCL) tunable between 7.6 and 8.3 μm wavelengths coupled into a single-mode hollow-core waveguide. Quartz-enhanced photoacoustic spectroscopy has been selected as detecting technique. The fiber coupling system converts the astigmatic beam exiting the laser into a TEM(00) mode. During a full laser scan, we observed no misalignment between the optical beam and the tuning fork, thus making our system applicable for multi-gas or broad absorber detections. The sensor has been tested on N₂:H₂S gas mixtures. The minimum detectable H₂S concentration is 450 ppb in ~3 s integration time, which is the best value till now reported in literature for H₂S optical sensors.