Laser driving and data processing concept for mobile trace gas sensing: Design and implementation

Abstract

High precision mobile sensing of multi-species gases is greatly demanded in a wide range of applications. Although quantum cascade laser absorption spectroscopy demonstrates excellent field-deployment capabilities for gas sensing, the implementation of this measurement technique into sensor-like portable instrumentation still remains challenging. In this paper, two crucial elements, the laser driving and data acquisition electronics, are addressed. Therefore, we exploit the benefits of the time-division multiplexed intermittent continuous wave driving concept and the real-time signal pre-processing capabilities of a commercial System-on-Chip (SoC, Red Pitaya). We describe a re-designed current driver that offers a universal solution for operating a wide range of multi-wavelength quantum cascade laser device types and allows stacking for the purpose of multiple laser configurations. Its adaptation to the various driving situations is enabled by numerous field programmable gate array (FPGA) functionalities that were developed on the SoC, such as flexible generation of a large variety of synchronized trigger signals and digital inputs/outputs (DIOs). The same SoC is used to sample the spectroscopic signal at rates up to 125 MS/s with 14-bit resolution. Additional FPGA functionalities were implemented to enable on-board averaging of consecutive spectral scans in real-time, resulting in optimized memory bandwidth and hardware resource utilisation and autonomous system operation. Thus, we demonstrate how a cost-effective, compact, and commercial SoC can successfully be adapted to obtain a fully operational research-grade laser spectrometer. The overall system performance was examined in a spectroscopic setup by analyzing low pressure absorption features of CO at 4.3 μm.

High-precision ethanol measurement by mid-IR laser absorption spectroscopy for metrological applications

“…The sample gas temperature and pressure are monitored by a high-precision NTC-thermistor (10 kΩ, BetaTHERM Sensors, Ireland) and an absolute capacitance manometer (722B, MKS Instruments, Inc., USA), respectively. The electronics compartment includes a power supply unit, an embedded computer, a temperature controller for the optical module temperature stabilization, the laser driver electronics, and an FPGA-based system-on-chip hardware-control and data acquisition module with a sampling rate of 125 MS/s and 14 bit resolution [21]. The custom-built laser driver is based on the concept of intermittent continuous wave (iCW) scanning.…”

Compact and Lightweight Mid-IR Laser Spectrometer for Balloon-borne Water Vapor Measurements in the UTLS

“…This partly open source hardware features a field programmable gate array (FPGA) and a microcontroller unit (MCU) running a GNU/Linux operating system. The FPGA on Red Pitaya has been reconfigured to provide the functionalities for high-resolution absorption spectroscopy (Liu et al, 2018;Tuzson et al, 2020).…”

“…In comparison to the generic continuous wave (CW) driving schemes, icw driving drastically reduces the energy consumption and, thus, the production of excess heat. The current ramps are generated by custom-developed analogue electronics (Liu et al, 2018).…”

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“…An extension of the observation record, spanning the last 800 kyr, has become possible using polar ice cores, from which small samples of past atmospheric air can be extracted. Thus, a reconstruction of the CO 2 , CH 4 , and N 2 O records over the entire anthropogenic era (Rubino et al, 2013;MacFarling Meure et al, 2006) and further back in time over past glacial-interglacial cycles covering up to the last 800 kyr was realized (Loulergue et al, 2008;Schilt, 2013;Bereiter et al, 2015;Petit et al, 1999;Lüthi et al, 2008). Apart from greenhouse gas concentrations in ice cores, which are often determined by gas chromatography (GC) techniques, the precise quantification of their isotopic composition using mass spectrometry (MS) or coupled gas chromatography-mass spectrometry (GC-MS) analyses of ice core samples has become possible in recent years (Schmitt et al, 2012;Schilt et al, 2014;Bock et al, 2017;Bauska et al, 2018).…”