Double-range near-infrared acetylene detection using a dual spot-ring Herriott cell (DSR-HC)

Design and fabrication of a dual spot-ring Herriott cell (DSR-HC) were proposed. The sealed Herriott cell with a dimensional size of 5.5 cm x 9.2 cm x 32.1 cm, possessed two input/output coupling holes leading to two absorption path lengths of similar to 20 m and similar to 6 m, respectively. An acetylene (C2H2) sensor system with a double-range was developed using the DSR-HC and wavelength modulation spectroscopy (WMS) technique. A near-infrared distributed feedback (DFB) laser was employed for targeting a C2H2 absorption line at 6521.2 cm(-1). C2H2 concentration measurements were carried out by modulating the laser at a 5 kHz frequency and demodulating the detector signal with LabVIEW software. An Allan-Werle deviation analysis indicated that the limit of detection (LoD) for the two absorption path lengths of 20 m and 6 m are 7.9 parts-per-million in volume (ppmv) and 4.0 ppmv, respectively. The DSR-HC concept can be used to fabricate similar cells for single-gas detection requiring two different detection ranges as well as for dual-gas detection requiring different absorption path lengths. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement