AS5.3

Laser-based spectroscopic methods, such as tunable diode laser absorption spectroscopy (TDLAS) ^[1] and quartz-enhanced photoacoustic spectroscopy (QEPAS) ^[2], have been developed for trace gas detection, leading to the advent of reliable and robust gas sensors. Among them, QEPAS is an attractive approach characterized by high cost-effectiveness, high sensitivity and small footprint, due to the use of a high Q-factor, low-cost quartz tuning fork (QTF) ^[3] as acoustic detector ^[4]. In the traditional single-pass QEPAS, modulated laser beam is focused at the QTF gap and only one acoustic source is generated between the QTF prongs. In the present work, multiple sound-source excitation has been applied to quartz-enhanced photoacoustic spectroscopy (MSSE-QEPAS) by using a single-line spot pattern multi-pass cell (MPC) ^[5]. The single-line spot pattern MPC is designed to make laser beam passing through the QTF 60 times to produce 60 acoustic sources between the QTF prongs. A signal gain factor of ~ 20 was realized in the MSSE-QEPAS approach with respect to the traditional single-pass QEPAS. A theoretical mode based on convolution method is proposed to modeling the MSSE-QEPAS approach. Highly sensitive QEPAS sensors based on MSSE-QEPAS described in this paper represents high opportunities for applications in atmospheric monitoring, industry process control and medical diagnostics.

Acknowledgments : The project is sponsored by National Key R&D Program of China (2019YFE0118200), National Natural Science Foundation of China (NSFC) (62075119, 61805132), Sanjin Scholar (2017QNSJXZ-04) and Shanxi “1331KSC”. Frank K. Tittel acknowledges support by the Robert Welch Foundation (Grant #C0586).

References

[1] R. Cui, L. Dong, H. Wu, W. Ma, L. Xiao, S. Jia, W. Chen, and F. K. Tittel, Anal. Chem. 92 (2020) 13034-1304.

[2] H. Wu, L. Dong, H. Zheng, Y. Yu, W. Ma, L. Zhang, W. Yin, L. Xiao, S. Jia, F. K. Tittel, Nat. Commun. 8 (2017) 15331.

[3] T. Wei, A. Zifarelli, S. Dello Russo, H. Wu, G. Menduni, P. Patimisco, A. Sampaolo, V. Spagnolo, L. Dong, Appl. Phys. Rev. 8 (2021) 041409.

[4] P. Patimisco, A. Sampaolo, L. Dong, F. K. Tittel, V. Spagnolo, Appl. Phys. Rev. 5 (2018) 011106.

[5] R. Cui, H. Wu, L. Dong, W. Chen, F. K. Tittel, Appl. Phys. Lett. 118 (2021) 161101.

How to cite: Cui, R., Wu, H., Tittel, F. K., Dong, L., and Chen, W.: Multiple-sound-source-excitation quartz-enhanced photoacoustic spectroscopy based on a single-line spot pattern multi-pass cell, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1534, https://doi.org/10.5194/egusphere-egu22-1534, 2022.

In the past decade, the rapid development of infrared laser technology has led to an increasing demand for photodetectors with high sensitivity and a wide operative spectral range suitable for spectroscopic applications ^[1-2]. In this work, we report on the performance of a custom quartz tuning fork (QTF), having a fundamental resonance frequency of 9.78 kHz and quality factor of 11500 at atmospheric pressure, which was used as a sensitive and broadband infrared photodetector for laser absorption spectroscopy ^[3]. Fourier infrared spectrometer was used to characterize the infrared absorption capacity of quartz material at the wavelength of 1-20 μm. Wide spectral response capability of the used QTF detector was investigated based on tunable diode absorption spectroscopy using lasers operating at five different wavelengths (1.6-10.35 μm). A spectrally flat responsivity of ~2.2 kV/W was demonstrated, corresponding to a noise-equivalent power of 1.5 nW/Hz^1/2, without employing any thermoelectrical cooling systems. In order to compensate for the drift of inherent characteristics (resonance frequency and quality factors) of the QTF detector, a heterodyne detection scheme was implemented to retrieve the resonance properties of the QTF detector together with the gas concentration in a single, fast measurement ^[4]. Experimental details including theoretical simulation and application demonstration will be discussed and presented.

Acknowledgments

The authors acknowledge financial support from National Key R&D Program of China (No. 2019YFE0118200), THORLABS GmbH, within PolySense, a joint-research laboratory, and the National Natural Science Foundation of China (Nos. 62075119 and 61805132).

References

[1] L. Dong, F. K. Tittel, C. Li, N. P. Sanchez, H. Wu, C. Zheng, Y. Yu, A. Sampaolo, and R. J. Griffin, Opt. Express 24 (2016) A528-A535.

[2] S. Dello Russo, A. Zifarelli, P. Patimisco, A. Sampaolo, T. Wei, H. Wu, L. Dong, and V. Spagnolo, Opt. Express 28 (2020) 19074-19084.

[3] T. Wei, A. Zifarelli, S. Dello Russo, H. Wu, G. Menduni, P. Patimisco, A. Sampaolo, V. Spagnolo, L. Dong, Appl. Phys. Rev. 8 (2021) 041409.

[4] H. Wu, L. Dong, H. Zheng, Y. Yu, W. Ma, L. Zhang, W. Yin, L. Xiao, S. Jia, and F. K. Tittel, Nat. Commun. 8 (2017) 15331.

How to cite: Wei, T., Zifarelli, A., Dello Russo, S., Wu, H., Menduni, G., Patimisco, P., Sampaolo, A., Vincenzo, V., Dong, L., and Chen, W.: High and flat spectral responsivity of quartz tuning fork used as infrared photodetector in tunable diode laser spectroscopy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1540, https://doi.org/10.5194/egusphere-egu22-1540, 2022.

The GrAnada Lightning Ultrafast Spectrograph (GALIUS) is a portable, ground-based slit spectrograph designed and developed at the Instituto de Astrofísica de Andalucía, in Granada, Spain. It is able to record spectra of natural and triggered lightning or lightning-like plasmas with submicrosecond time resolution in a spectral range from 380 nm to 854 nm. Our work shows GALIUS radial-resolved slit spectroscopy of 20 laboratory produced lightning-like discharges of 30 mm length and 8 ± 2 mm mean width, generated with an automated Wimshurst machine, being their mean peak voltage and current 32.70 kV and 149.58 A, respectively. We analyze the visible (645.0 - 663.0 nm) region operated at 900 kfps with 0.79 µs exposure time, spectral resolution better than 0.38 nm and spectral dispersion of 0.58 mm/px, that allows us to experimentally quantify the profiles of electron density and electron/gas temperature along the radial dimension of the lightning-like plasma channels and their temporal dynamics. To do so, we analyze the rows of the 2D spatial-spectral images of the heated channel of every lightning-like discharge, to follow the radial and temporal variation of neutral (atoms and molecules) and ion spectroscopic signatures. From these measurements we also estimate the evolution of the radial profiles of electrical conductivity, overpressure and populations of key chemical species(N₂, NO, O₂, OH, H₂, N₂O, NO₂, HO₂, O₃ and H₂O) produced along the radius of the plasma channel.

How to cite: Passas-Varo, M., Gordillo-Vázquez, F. J., Sánchez del Río, J., and Kieu, T. N.: Experimental radial profiles of early time (< 4 μs) neutral and ion spectroscopic signatures in lightning-like discharges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2860, https://doi.org/10.5194/egusphere-egu22-2860, 2022.

The intensive development of industry, agriculture, and transportation causes many issues related to the negative impact on the environment and human health. Harmful products of human technogenic activity accumulate in the environment. Due to increasing concentrations of greenhouse gases (methane, carbon dioxide, etc.), the effects of global warming are already being observed. Research that addresses the challenges of climate change mitigation and creates science-based assumptions for new environmental monitoring systems and technologies is becoming more and more relevant.

A new two drone system with a variable optical path for measuring greenhouse gases (CH₄, CO₂) is currently in development. Here, we will present a distributed feedback (DFB) quantum cascade laser absorption spectroscopy system which is used for measuring methane concentrations in the atmosphere. The DFB laser for methane measurements is being operated at 3371.5 nm and 3368.8 nm, for higher and lower concentrations respectively.

The results of the Allan-Werle deviation analysis will be introduced. Also, measurement capabilities and detection limits of the system will be presented and discussed.

How to cite: Butkus, L., Ežerinskis, Ž., Plotnikov, A., Koroliov, A., Šapolaitė, J., Pabedinskas, A., Plukis, A., and Remeikis, V.: Distributed feedback quantum cascade laser absorption spectroscopy for airborne methane measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6174, https://doi.org/10.5194/egusphere-egu22-6174, 2022.

Buffer gas cooling relies on the thermalization of a buffer gas with a surface brought to cryogenic temperatures, which in turn thermalizes the target molecules through collisions. Because this process does not rely on any particular energy pattern, any molecule can be brought to the temperature of the buffer gas. Advantages of buffer gas cooling are numerous: it is a continuous source of slow laboratory frame velocities, allowing for long observation times. Moreover, in contrast to supersonic expansion, it does not require important pumping infrastructure because it relies on small gas throughput and cryogenic pumping (Changala et al., Appl. Phys. B 122 (2016) 292). Finally, buffer gas cooling is applicable to nearly all molecules and is very efficient in terms of sample density (Santamaria et al., ApJ 801 (2015) 50). The technique requires continuous injection of helium atoms and the species under study inside a vacuum chamber. We developed a cavity ringdown spectroscopy setup to seek the first cold molecules obtained with our apparatus.

One of our first molecular targets is a six-atoms asymmetric top molecule and the smallest molecule to present internal rotation: methanol (CH₃OH).
The size of this molecule and the presence of this large amplitude motion lead to a dense and disordered rotational structure. This structure gets even more complicated when one goes up in energy with vibrational excitations. Due to its complicated spectrum, this molecule remains poorly known, especially in the NIR. This frequency range was recently explored by Svoboda et al. (Phys. Chem. Chem. Phys., 17 (2015) 15710), probing the 2ν₁ vibration overtone around 7200 cm^-1. In this report, the authors were able to assign on the order of a few percent of the observed lines. It thus seemed to be a promising candidate to challenge our ability to record and understand the spectral signature of large molecules in the overtone range using the cooling efficiency of the buffer gas cooling setup and the sensitivity of the cavity ringdown spectrometer.

The experiment and the spectra of CH₃OH will be discussed. The floor will be open for discussion to identify new targets of astrophysical or atmospheric interest.

How to cite: Libert, A., Robert, S., Fabre, B., Kassi, S., Roucou, A., Glorieux, R., Daman, M., Vanlancker, G., Hays, B., and Lauzin, C.: A Buffer Gas Cooling experiment coupled to Cavity Ring Down Spectroscopy to explore complex spectra in the Near-Infrared range, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9108, https://doi.org/10.5194/egusphere-egu22-9108, 2022.

A large number of Earth atmosphere observation missions based on Fourier Transform Spectroscopy produce interferograms, which are then processed for being used as spectral radiances. The idea that the useful information for retrieving a given set of atmospheric variables is concentrated in a small portion of the interferogram appeared in the late 1970s [1], [2]. More recently, the interest of such an approach has been demonstrated for the nadir measurement of atmospheric trace components (CO2, CO, CH4 and N2O): the biases induced by the uncertainties on H2O and temperature profiles are largely reduced and the method is totally insensitive to the ground background in IASI-Metop spectral range. Moreover, performing inversions directly on partial interferograms allows improving the signal-to-noise ratio of the data to be processed and thus the instrumental sensitivity [3], [4].
We are currently developing new spectro-imagers founded on the acquisition of partial interferograms, based on an innovative concept of static Fourier transform spectro-imager called imSPOC  [5]. In the framework of the Strategic Research Initiative SPACEOBS, which aims at setting up a "space incubator", a laboratory demonstrator for the measurement of the CO total column measurement in solar occultation mode has been built. Its potential application is the estimation of anthropogenic emissions in urban area [6].  The  imSPOC concept is also evaluated for the measurement of anthropogenic CO2 and CH4 emissions from a constellation of small satellites [7],[8].
Based on these developments, a retrieval algorithm for the simulation and exploitation of the imSPOC partial interferograms has been developed. This algorithm allows performing calculations with (i) a forward approach (performance assessment in the design phase) and (ii) a backward approach (performance assessment and optimization in the design phase, and exploitation of the acquired data). The interferograms can be generated on regular or non-regular grid of optical path differences, and the transmissions of the instrument and the interferometric cavity can be analytically calculated or experimentally determined.  It is also possible to directly work on radiances, without computing any interferograms. We will present an application of this algorithm to the performance assessment of the CO prototype and we will demonstrate the interest of such concepts and the possibility of jointly retrieving geophysical parameters such as the total column of CO and H2O and instrumental parameters such as the temperature of the interferometer from a partial interferogram.
[1]    T. G. Kyle, Appl. Opt., vol. 16, no 2, p. 326 333, févr. 1977.
[2]    G. Fortunato, J. Opt., vol. 9, no 5, p. 281, 1978.
[3]    C. Serio et al, in Atmospheric Model Applications, Intech, 2012.
[4]    G. Grieco et al., Appl. Opt., vol. 50, no 22, p. 4516 4528, août 2011.
[5]    patent WO2018002558A1
[6]    S. Gousset et al.  (2018, April). On the use of partial interferograms for GHG measurement using a solar occultation geometry. In EGU General Assembly Conference Abstracts (p. 12035).
[7]    L. Brooker Lizon-Tati et al., International Astronautical Congress (IAC), 2018.
[8]    M. Dogniaux et al., Atmospheric Measurement Techniques Discussions, 1-38.

How to cite: Croize, L., Payan, S., and Ferrec, Y.: Joint retrieval of geophysical and instrumental parameters from partially sampled interferograms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10125, https://doi.org/10.5194/egusphere-egu22-10125, 2022.

The usefulness of the equally spaced, phase-coherent, narrow-band spectral lines of a frequency combs (FC) for spectroscopy has long been recognized for applications in gas-phase sensing. Among the different type of frequency combs the gain switching of commercially available semiconductor lasers in the near IR has recently gained interest due to the simplicity and flexibility of this approach [1, 2]. In this study we present a custom-designed gain-switched frequency comb (GSFC) with a small free spectral range of merely 100 MHz [3]. This GSFC was passively coupled to a medium finesse (F = 520) cavity in off-axis configuration for the detection of ammonia (¹⁴NH₃) in static dry air [4]. The absorption of ammonia was measured between 6604.5 and 6606.0 cm^-1 using a Fourier transform spectrometer. More than 60 lines of the GSFC overlapped with the strongest ro-vibrational ammonia absorption features in that spectral region. With the cavity in off-axis configuration, an NH₃ detection limit of ~5 ppmv in 20 s was accomplished in a static laboratory environment. The characterization and experimental performance of the GSFC and prototype spectrometer are presented in this contribution together with a discussion of the corresponding technical advantages and drawbacks, as well as the potential for alternative future applications.

Acknowledgement

This publication has emanated from research supported in part by Grants from Science Foundation Ireland with the numbers 21/FFP-A/8973, 15/CDA/3640, and 14/TIDA/2415. Financial support by Enterprise Ireland’s Commercialization Fund (CF 2017 0683) is also gratefully acknowledged.

References

[1] P.M. Anandarajah, R. Maher, Y. Xu, S. Latkowski, J. O’Carroll, S.G. Murdoch, R. Phelan, J. O’Gorman, L.P. Barry, IEEE Photonics J. 3 (2011) 112. Doi: 10.1109/jphot.2011.2105861

[2] M.D. Guitérrez-Pascual,V. Vujicic, J. Braddell, F. Smyth, P.M. Anandarajah, L.P. Barry, Opt. Lett. 42 (2017) 555. Doi: 10.1364/OL.42.000555

[3] A. Rosado, E. P. Martin, A. Pérez-Serrano, J. M. G. Tijero, I. Esquivias, P. M. Anandarajah, Opt. Laser Technol. 131 (2020) 106392. Doi: 10.1016/j.optlastec.2020.106392

[4] S. Chandran, A.A. Ruth, E.P. Martin, J.K. Alexander, F.H. Peters, P.M. Anandarajah, Sensors 19 (2019) 5217. Doi: 10.3390/s19235217

How to cite: Ruth, A. A., Chandran*, S., Martin, E. P., Rosado, A., Soderholm, E. P., Alexander, J. K., Peters, F. H., and Anandarajah, P. M.: Ammonia Sensing with a Gain Switched Frequency Comb of 100 MHz Free Spectral Range using Off-Axis Cavity-Enhanced Absorption Spectroscopy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10136, https://doi.org/10.5194/egusphere-egu22-10136, 2022.

Reliable sub-ppb monitoring of reactive trace gas concentrations is essential for industrial and air quality monitoring purposes. Calibrating reactive trace gas analyzers is challenging because of the lack of certified primary standards.

Here we present a three-fold approach for calibration (validation) of Picarro’s Cavity Ring-Down analyzers (CRDS) for reactive trace gas monitoring: (i) calibration of a golden analyzer, (ii) validation of linearity using a surrogate gas approach, and (iii) accurate determination of the zero value. We use formaldehyde (H₂CO) to highlight best practices for QA/QC of reactive trace gas measurements and we demonstrate that this strategy can be applied to other reactive trace gases, such as NH₃, HCl, H₂O₂, and HF.

• The golden analyzer approach is based on a carefully calibrated inhouse reference instrument that is used as a transfer standard to cross-calibrate production units. After initial scaling based on the spectroscopy of Saha et al. [1], we present new data of primary formaldehyde standards (Apel-Riemer) that are used to adjust the scale of the golden formaldehyde analyzer.
• The surrogate gas validation approach is based on the principle that the accurarcy and linearity of the analyzer can be validated using a surrogate gas standard that is non-reactive, commercially available, and has a spectral adsorption line adjacent to the primary gas. In the case of formaldehyde, methane (CH₄) meets these criteria, and using methane standards therefore remove the need for regularly measuring formaldehyde standards.
• Accurate and regular determination of the zero value of a trace gas analyzer is key to achieve the highest data quality. We discuss the use of different scrubbing agents (DrieRite, 4,2-DNPH cartridges, activated charcoal) in combination with an automated valve switching procedure to track the zero drift of the G2307 formaldehyde analyzer (typically <0.33ppb in 72hrs).

Reference

[1] Saha et al., Molecular Physics, 2007

How to cite: Hofmann, M. E. G., Bent, J., and van Zwieten, R.: Innovative calibration strategies for quality assurance and quality control of reactive trace gas analyzers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10337, https://doi.org/10.5194/egusphere-egu22-10337, 2022.