Sensitive trace gas detection with cavity enhanced absorption spectroscopy using a continuous wave external-cavity quantum cascade laser

Helden, J. H. van; Lang, N.; Macherius, U.; Zimmermann, H.; Röpcke, J.

doi:10.1063/1.4823545

Cited by 51 publications

(38 citation statements)

References 23 publications

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“…The performance of narrowband WMS detection is comparable to recent EC-QCL-based WMS setups [8,9,12] and close to cavity-enhanced spectrometers [10,13]. The sensitivity was ultimately limited by fluctuations in the wavelength-dependent background caused by fringes.…”

Section: Discussionsupporting

confidence: 52%

“…Such external-cavity QCLs (EC-QCLs) also offer a large (~100 cm −1 ) mode-hop-free tuning range and high-bandwidth fine tuning via piezoelectric elements and laser injection current [1,5]. Consequently, EC-QCLs have been used for highresolution broadband absorption spectroscopy [6,7], as well as for sensitive narrowband detection in environmental, combustion and medical applications [8][9][10][11][12][13]. Given the high output power, EC-QCLs are also well-suited for photo-acoustic spectroscopy [14].…”

Section: Introductionmentioning

confidence: 99%

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Real-time breath gas analysis of CO and CO2 using an EC-QCL

Ghorbani

Schmidt

2017

Appl. Phys. B

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Section: Discussionsupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Real-time breath gas analysis of CO and CO2 using an EC-QCL

Ghorbani

Schmidt

2017

Appl. Phys. B

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“…The included cavity-enhanced absorption spectroscopy [12], quartz-enhanced photoacoustic spectroscopy [13, 14], and open-path setups [15–17] were all successfully applied to industrial and environmental monitoring. The “golden standard” for QCL-based trace gas measurements in the MIR spectral region is established on absorbance measurements in multipass-reflection cells [18].…”

Section: Introductionmentioning

confidence: 99%

Implementation of a quantum cascade laser-based gas sensor prototype for sub-ppmv H2S measurements in a petrochemical process gas stream

et al. 2016

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The implementation of a sensitive and selective as well as industrial fit gas sensor prototype based on wavelength modulation spectroscopy with second harmonic detection (2f-WMS) employing an 8-μm continuous-wave distributed feedback quantum cascade laser (CW-DFB-QCL) for monitoring hydrogen sulfide (H2S) at sub-ppm levels is reported. Regarding the applicability for analytical and industrial process purposes aimed at petrochemical environments, a synthetic methane (CH4) matrix of up to 1000 ppmv together with a varying H2S content was chosen as the model environment for the laboratory-based performance evaluation performed at TU Wien. A noise-equivalent absorption sensitivity (NEAS) for H2S targeting the absorption line at 1247.2 cm−1 was found to be 8.419 × 10−10 cm−1 Hz−1/2, and a limit of detection (LOD) of 150 ppbv H2S could be achieved. The sensor prototype was then deployed for on-site measurements at the petrochemical research hydrogenation platform of the industrial partner OMV AG. In order to meet the company’s on-site safety regulations, the H2S sensor platform was installed in an industry rack and equipped with the required safety infrastructure for protected operation in hazardous and explosive environments. The work reports the suitability of the sensor prototype for simultaneous monitoring of H2S and CH4 content in the process streams of a research hydrodesulfurization (HDS) unit. Concentration readings were obtained every 15 s and revealed process dynamics not observed previously.

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“…However, a long effective path requires highly reflective cavity mirrors, and as the mirror reflectivity increases, less light exits the cavity [6]. In fact, the transmitted light intensity decreases at the same rate as L eff increases, and, since the signal generally is measured by an IR detector outside the cavity, extended effective path lengths make it increasingly difficult to measure the signal [3,4,6,7]. The reduction of signal strength has to be countered by employing more advanced, expensive and complicated detectors, and, hence, the currently used signal-detection technology has become a limiting factor in the continued development of commercial cavity-enhanced IR spectroscopy [5,7].…”

Section: Introductionmentioning

confidence: 99%

“…In some applications, where the sensitivity and limit-of-detection (LOD) are of extra importance, current IR spectroscopy relies on different cavity-enhanced methods, e.g., cavity ring-down spectroscopy (CRDS) [2], intracavity absorption spectroscopy (ICAS) [3], and integrated cavity output spectroscopy (ICOS) [4]. In all these methods, the spectroscopic signal is enhanced by letting the laser beam pass repeatedly through the sample, via multiple reflections between parallel mirrors.…”

Section: Introductionmentioning

confidence: 99%

Improved optogalvanic detection with voltage biased Langmuir probes

Persson

Berglund

Salehpour

2014

Journal of Applied Physics

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Optogalvanic detectors show great potential for infrared spectroscopy, especially in cavity enhanced techniques where they, in contrast to ordinary absorption detectors, can perform intracavity measurements. This enables them to utilize the signal-to-noise ratio improvement gained from the extended effective path length inside an optical cavity, without losing signal strength due to the limited amount of light exiting through the rear mirror.However, if optogalvanic detectors are to become truly competitive, their intrinsic sensitivity and stability has to be improved. This, in turn, requires a better understanding of the mechanisms behind the generation of the optogalvanic signal. The study presented here focuses on an optogalvanic detector based on a miniaturized stripline split-ring resonator plasma source equipped with Langmuir probes for detecting the optogalvanic signal. In particular, the effect of applying a constant bias voltage to one of the probes is investigated, both with respect to the sensitivity and stability, and to the mechanism behind the generation of the signal. Experiments with different bias voltages at different pressures and gas composition have been conducted. In particular, two different gas compositions (pure CO 2 and 0.25% CO 2 in 99.75% N 2 ) at six different pressures (100 Pa to 600 Pa) have been studied. It has been shown that probe biasing effectively improves the performance of the detector, by increasing the amplitude of the signal linearly over one order of magnitude, and the stability by about 40% compared with previous studies. Furthermore, it has been shown that relatively straightforward plasma theory can be applied to interpret the mechanism behind the generation of the signal, although additional mechanisms, such as rovibrational excitation from electron-molecule collisions, become apparent in CO 2 plasmas with electron energies in the 1-6 eV range. With the achieved performance improvement and the more solid theoretical framework presented here, stripline split-ring resonator optogalvanic detectors can evolve into a compact, inexpensive and easy-to-operate alternative for future infrared spectrometers.

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Sensitive trace gas detection with cavity enhanced absorption spectroscopy using a continuous wave external-cavity quantum cascade laser

Cited by 51 publications

References 23 publications

Real-time breath gas analysis of CO and CO2 using an EC-QCL

Real-time breath gas analysis of CO and CO2 using an EC-QCL

Implementation of a quantum cascade laser-based gas sensor prototype for sub-ppmv H2S measurements in a petrochemical process gas stream

Improved optogalvanic detection with voltage biased Langmuir probes

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