RES-Q-Trace: A Mobile CEAS-Based Demonstrator for Multi-Component Trace Gas Detection in the MIR.

Norbert Lang,Mathias Wiese,Jürgen Röpcke,Jean-Pierre H Van Helden,Henrik Zimmermann,Uwe Macherius,Sven Glitsch

doi:10.3390/s18072058

Abstract

Sensitive trace gas detection plays an important role in current challenges occurring in areas such as industrial process control and environmental monitoring. In particular, for medical breath analysis and for the detection of illegal substances, e.g., drugs and explosives, a selective and sensitive detection of trace gases in real-time is required. We report on a compact and transportable multi-component system (RES-Q-Trace) for molecular trace gas detection based on cavity-enhanced techniques in the mid-infrared (MIR). The RES-Q-Trace system can operate four independent continuous wave quantum or interband cascade lasers each combined with an optical cavity. Twice the method of off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) was used, twice the method of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS), respectively. Multi-functional software has been implemented (i) for the general system control; (ii) to drive the four different laser sources and (iii) to analyze the detector signals for concentration determination of several molecular species. For the validation of the versatility and the performance of the RES-Q-Trace instrument the species NO, N2O, CH4, C2H4 and C3H6O, with relevance in the fields of breath gas analysis and the detection of explosives have been monitored in the MIR with detection limits at atmospheric pressure in the ppb and ppt range.

Highlights

For more than a decade, a broad variety of applications invigorating efforts to further improve the sensitivity of technologies for trace gas detection have been required
The usage of laser sources operating in the mid-infrared (MIR, 3–20 μm), such as quantum cascade lasers (QCLs) or interband cascade lasers (ICLs), enables access to the strong fundamental vibrational bands of many molecular species and, opens up the possibility of detecting them up Sensors 2018, 18, 2058; doi:10.3390/s18072058
For the discrimination of the laser beams passing through the multipass optical cell time, multiplexing techniques must be applied, this could be realized in the kHz regime

Summary

Introduction

For more than a decade, a broad variety of applications invigorating efforts to further improve the sensitivity of technologies for trace gas detection have been required. This applies to the development, optimization and controlling of industrial production processes, and to the field of medical breath analysis [1] and to the detection of illegal substances, such as drugs and explosives [2], where detection sensitivities down to part per billion (ppb) and part per trillion (ppt) levels are required. About four hundred VOCs occur only at ppb or ppt levels [1]. The usage of laser sources operating in the mid-infrared (MIR, 3–20 μm), such as quantum cascade lasers (QCLs) or interband cascade lasers (ICLs), enables access to the strong fundamental vibrational bands of many molecular species and, opens up the possibility of detecting them up Sensors 2018, 18, 2058; doi:10.3390/s18072058 www.mdpi.com/journal/sensors

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