title: Application of a ring cavity surface emitting quantum cascade laser (RCSE-QCL) on the measurement of H2S in a CH4matrix for process analytics.
abstract: The present work reports on the first application of a ring-cavity-surface-emitting quantum-cascade laser (RCSE-QCL) for sensitive gas measurements. RCSE-QCLs are promising candidates for optical gas-sensing due to their single-mode, mode-hop-free and narrow-band emission characteristics along with their broad spectral coverage. The time resolved down-chirp of the RCSE-QCL in the 1227-1236 cm-1(8.15-8.09 µm) spectral range was investigated using a step-scan FT-IR spectrometer (Bruker Vertex 80v) with 2 ns time and 0.1 cm-1spectral resolution. The pulse repetition rate was set between 20 and 200 kHz and the laser device was cooled to 15-17°C. Employing 300 ns pulses a spectrum of ~1.5 cm-1could be recorded. Under these laser operation conditions and a gas pressure of 1000 mbar a limit of detection (3σ) of 1.5 ppmv for hydrogen sulfide (H2S) in nitrogen was achieved using a 100 m Herriott cell and a thermoelectric cooled MCT detector for absorption measurements. Using 3 µs long pulses enabled to further extend the spectral bandwidth to 8.5 cm-1. Based on this increased spectral coverage and employing reduced pressure conditions (50 mbar) multiple peaks of the target analyte H2S as well as methane (CH4) could be examined within one single pulse.
authors.forename: Harald
authors.initials: H
authors.lastname: Moser
authors.forename: Andreas
authors.initials: A
authors.lastname: Genner
authors.forename: Johannes
authors.initials: J
authors.lastname: Ofner
authors.forename: C
authors.initials: C
authors.lastname: Schwarzer
authors.forename: Gottfried
authors.initials: G
authors.lastname: Strasser
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lendl