Multipass Gas Cell Research Articles

A mid-infrared exhaled carbon dioxide isotope detection system based on 4.35 μm quantum cascade laser

The carbon dioxide isotope in human exhaled gas can be used as an indicator to determine Helicobacter pylori (HP), the detection of carbon dioxide isotope in human exhaled gas is of great significance for the treatment of human diseases. Based on Tunable Diode Laser Absorption Spectroscopy (TDLAS), a carbon dioxide isotope detection system for exhaled gas was developed to detect the carbon dioxide isotope in human exhaled gas, a 4.35 μm quantum cascade laser (QCL) and a 3 m optical path multi-pass gas cell (MPGC) were adopted in the detection system. The exhaled gas pretreatment system was designed to pass through human exhaled gas into the MPGC. The performance of the system was researched using a gas distribution station fitted with standard 12CO2 and 13CO2 concentrations. The results show that the limits of detection（LOD）of 12CO2 and 13CO2 reach up ∼ 0.0134 ppm and ∼ 0.0149 ppm, respectively. The detection precision of the system is ∼ 0.00214 ‰ with a 48 s averaging time. QCL-based mid-infrared detection system has higher sensitivity and lower detection limit compared with near-infrared detection system. The volume of MPGC is 250 ml, which is much less than the volume of normal human exhaled gas, therefore the majority of human exhaled gas can be filled with MPGC. Two-stage proportional-integral-derivative (PID) temperature control is adopted to eliminate the effect of drift of the spectrum due to the change of temperature, so that the stability of the system is improved. A high precision and high-speed Genetic Algorithm Extreme Learning Machine (GA-ELM) algorithm is applied for improving the concentration inversion precision of the system. Finally, the performance of detection system was validated at Sichuan Cancer Hospital for detecting carbon dioxide isotope in exhaled gas, and the verification results illustrate that the detection system has a very important application prospect in the field of exhaled gas detection.

A near‐infrared CO2 detection system for greenhouse gas based on PCA‐DNN

AbstractCarbon dioxide (CO2) gas is one of the main greenhouse gases. The detection of CO2 gas content is of great significance to the study of the greenhouse effect. The CO2 detection system based on the principle of tunable diode laser absorption spectroscopy (TDLAS) was demonstrated. A distributed feedback (DFB) laser with a central wavelength of 1580 nm was used as the laser source, multipass gas cell (MPGC) was used as gas cell, and indium gallium arsenic (IGA) photodetector was used to complete photoelectric conversion, and the original extracted second harmonic signal was smooth and denoised by wavelet transform. The signal‐to‐noise ratio (SNR) of the wavelet‐filtered spectrum improved from 6.88 to 13.87 dB, an improvement of 2.02 times. Principal component analysis was used to reduce the complexity of the data by compressing the spectrum from 800 dimensions to 2 dimensions. For the concentration inversion, the back‐propagation deep neural network (BP‐DNN) model was used to perform standard gas concentration step experiments and compared with the back‐propagation neural network (BPNN). The experimental results show that the BP‐DNN inversion of CO2 concentration has improved computational accuracy and the root mean square error (RMSE) is 3.55 times lower than that of the traditional BPNN, showing favorable application prospects.

Vehicle‐mounted mobile mid‐infrared high‐precision atmospheric ethane sensor system

AbstractEthane (C2H6) is an important gas in environmental monitoring, especially in urban areas, and the development of vehicle‐mounted mobile C2H6 sensors is meaningful for high‐efficiency and wide‐range detection of C2H6 concentration levels. Based on tunable diode laser absorption spectroscopy, a sensor system for the detection of trace C2H6 concentration in the atmosphere was developed using wavelength modulation spectroscopy. An interband cascade laser with a central wavelength of 3337 nm and a multipass gas cell (MPGC) with an optical path length of 26.4 m was used as core optical components. The pressure in the MPGC was optimized at 200 Torr, and such pressure was stabilized by a self‐developed pressure control system. The sensor system was compactly integrated into a standalone instrument with a dimension size of 52 × 33 × 28.8 cm3. The detection limit (1σ) was measured to be 3.45 parts per billion at an averaging time of 0.5 s. Forty‐eight‐hour field experiment and vehicle‐mounted mobile measurement of atmospheric C2H6 levels with concentration mapping were carried out on the Jilin University campus to validate the practical application ability of the system.

Oxygen detection system based on TDLAS–WMS and a compact multipass gas cell

AbstractIn this paper, a sensitive oxygen monitoring system was demonstrated using tunable diode laser absorption spectroscopy and wavelength modulation spectroscopy. Light from a distributed feedback laser near 760.8 nm was coupled into a compact Herriott cell with a 3.3 m optical path. A LabVIEW‐based orthogonal lock‐in amplifier was developed to extract the gas concentration information from the absorption signal, which can achieve baseline fitting, background deduction, filtering, and harmonic extraction. Oxygen measurement experiments were conducted, and the performance of the system was obtained. Based on an Allan deviation analysis, the minimum detection limit of the system was 0.247% at an averaging time of 1 s and could improve to 0.022% when the averaging time was 40 s.

A Laser-Based Multipass Absorption Sensor for Sub-ppm Detection of Methane, Acetylene and Ammonia.

A compact, sensitive laser-based absorption sensor for multispecies monitoring of methane (CH4), acetylene (C2H2) and ammonia (NH3) was developed using a compact multipass gas cell. The gas cell is 8.8 cm long and has an effective optical path length of 3.0 m with a sampling volume of 75 mL. The sensor is composed of three fiber-coupled distributed feedback lasers operating near 1512 nm, 1532 nm and 1654 nm, an InGaAs photodetector and a custom-designed software for data acquisition, signal processing and display. The lasers were scanned over the target absorption features at 1 Hz. First-harmonic-normalized wavelength modulation spectroscopy (f = 3 kHz) with the second harmonic detection (WMS-2f/1f) is employed to eliminate the unwanted power fluctuations of the transmitted laser caused by aerosol/particles scattering, absorption and beam-steering. The multispecies sensor has excellent linear responses (R2 > 0.997) within the gas concentration range of 1–1000 ppm and shows a detection limit of 0.32 ppm for CH4, 0.16 ppm for C2H2 and 0.23 ppm for NH3 at 1 s response time. The Allan–Werle deviation analysis verifies the long-term stability of the sensor, indicating a minimal detection limit of 20–34 ppb were achieved after 60–148 s integration time. Flow test of the portable multispecies sensor is also demonstrated in this work.

A compact self-calibration atmospheric CH4 sensor based on NIR laser and new type multi-pass gas cell

A near-infrared (NIR) laser-based optical sensor was developed for atmospheric methane (CH4) measurement. The sensor adopted a distributed feedback (DFB) fiber laser operating at ∼ 2334 nm as the light source. A compact new type multi-pass gas cell (MPGC) with 41.5 m effective optical path length (EOPL) and a high-speed data acquisition (DAQ) card with 1 million samples per second (MS/s) sample rate were utilized to improve the system performance. A self-calibration method was used to solve the problem of needing periodic external intervention for concentration calibration which has been encountered in traditional wavelength modulation spectroscopy (WMS) technology-based sensor system. For the selected CH4 molecule absorption line, located at 4284.512 cm−1, a detection limit (three-sigma value (3σ)) of 0.66 parts per million by volume (ppmv) at ambient temperature and pressure was achieved. Allan deviation analysis results indicate that measurement precision of 0.17 ppmv was obtained with a 1-s integration time, which could be further optimized to 0.03 ppmv by averaging up to ∼ 83 s. The CH4 concentration measurement both in the lab and in the field were carried out successively, which demonstrates the stability and robustness of the developed sensor.

Non-destructive mid-IR spectroscopy with quantum cascade laser can detect ethylene gas dynamics of apple cultivar \u2018Fuji\u2019 in real time

Many plants, including fruits and vegetables, release biogenic gases containing various volatile organic compounds such as ethylene (C2H4), which is a gaseous phytohormone. Non-destructive and in-situ gas sampling technology to detect trace C2H4 released from plants in real time would be attractive for visualising the ageing, ripening, and defence reactions of plants. In this study, we developed a C2H4 detection system with a detection limit of 0.8 ppb (3σ) using laser absorption spectroscopy. The C2H4 detection system consists of a mid-infrared quantum cascade laser oscillated at 10.5 µm, a multi-pass gas cell, a mid-IR photodetector, and a gas sampling system. Using non-destructive and in-situ gas sampling, while maintaining the internal pressure of the multi-pass gas cell at low pressure, the change in trace C2H4 concentration released from apples (Malus domestica Borkh.) can be observed in real time. We succeeded in observing C2H4 concentration changes with a time resolution of 1 s, while changing the atmospheric gas and surface temperature of apples from the ‘Fuji’ cultivar. This technique allows the visualisation of detailed C2H4 dynamics in plant environmental response, which may be promising for further progress in plant physiology, agriculture, and food science.

A trace CH4 detection system based on DAS calibrated WMS technique

We report the development of a compact near-infrared (NIR) laser-based trace methane (CH4) detection system. This detection system relied on a 2334 nm distributed feedback (DFB) fiber laser as the light source. A parallel dense light-spot pattern multipass gas cell (MGC) with 41.5 m effective absorption path length was utilized to improve the system sensitivity. A self-calibration approach based on direct absorption spectroscopy (DAS) calibrated wavelength modulation spectroscopy (WMS) technique was employed to solve the problem of extra concentration calibration requirement in traditional WMS technique, and to improve the accuracy and stability of the system. According to the Allan deviation analysis, 1-s measurement precision of 0.61 ppmv for DAS and 0.16 ppmv for WMS was obtained, which could be further reduced to 0.11 ppmv for DAS and 0.03 ppmv for WMS by averaging up to 80 s and 50 s, respectively. A week-long continuous atmospheric CH4 concentration measurement was also carried out to demonstrate the long-term performance of our CH4 detection system. With a fast dynamic response characteristics, high-accuracy and high-sensitivity, the proposed detection system is suitable for CH4 measurement in many fields such as atmospheric chemistry analyzation, industrial safety monitoring, agricultural information acquisition, etc.

Portable membrane inlet mass spectrometric detection and analysis of chemical warfare agent simulants at the U.S. Army Dugway Proving Ground S/K challenge event

There has been a significant demand for the development and improvement of technology used for the detection and identification of Chemical Warfare Agents (CWAs). Some of the current detection technology being used by the U.S. government includes multipass gas cell coupled Fourier Transform Infrared (FTIR) spectroscopy and Lightweight Chemical Detectors (LCD) systems. While these systems possess adequate sensitivity to detect CWAs in general, their analysis times are not considered 'rapid' nor are they able to identify the specific CWA. The U.S. Army Dugway Proving Ground's annual S/K Challenge event provides the opportunity to assess the performance and reliability of prospective detection instrumentation being developed by researchers worldwide to optimize their performance. To do so, trial testing of CWA simulants in both indoor and outdoor environments was performed, mimicking past attack scenarios. Membrane Inlet Mass Spectrometric (MIMS) technology on a portable system was successful in performing a rapid analysis along with identification of each CWA simulant utilized during the trials. The MIMS system can detect and quantify low-mass permeable compounds with parts-per-trillion limits of detection. This allows for analysis to be achieved within seconds after the initial exposure time, which is significantly faster than the FTIR and LCD systems currently used.

Line intensities of the 01111–00001 magnetic dipole absorption band of 12C16O2: Laboratory measurements

The spectra of carbon dioxide in the 3.3 µm region were recorded at three pressures using Bruker IFS 125 HR Fourier transform spectrometer and a 30 m base multipass gas cell of V.E. Zuev Institute of Atmospheric Optics SB RAS. Several lines of the 01111–00001 (ν2 + ν3) magnetic dipole band of 12C16O2 were detected and their line intensities were measured. The vibrational transition magnetic dipole moment was fitted to the observed line intensities. The fitted value of the vibrational transition magnetic dipole moment of 0.71(1)µN is substantially smaller than the value of 0.96µN obtained in the result of the analysis of the Martian atmosphere spectra (here µN is the nuclear magneton). Using the known set of the effective Hamiltonian parameters and fitted value of the vibrational transition magnetic dipole moment the list of the line parameters of this band was generated for the HITRAN database. In addition the line intensities of the R-branch of the electric dipole 01111–00001 band of the 16O12C18O isotopologue were measured for the first time.

The foreign-continuum absorption of water vapour in the far-infrared (50–500 cm−1)

We investigated the continuum absorption of water vapour diluted in nitrogen, oxygen and air in the range of the pure rotational band of the water molecule (50-500 cm−1). Spectra recordings were performed at room temperature with a Fourier transform spectrometer associated to a 151-m multipass gas cell located at the AILES beamline of SOLEIL synchrotron facility. The study includes the first laboratory measurements in the wide 90-330 cm−1 interval. Tests of the baseline stability, crucial for the continuum determination, are reported together with the expected pressure dependences of the continuum absorption, measured over different pressure ramps. Retrieved foreign-continuum cross-sections are found in good agreement with literature values available in the lower and upper parts of the studied frequency range. The reported results validate the MT_CKD foreign-continuum empirical model, widely used in atmospheric applications, even if some overestimation of the MT_CKD values is noted in the centre of the band where experimental data were absent.

Continuous monitoring of chemical warfare agents in vapor using a Fourier transform infra-red spectroscopy instrument with multi pass gas cell, mercury cadmium telluride detector and rolling background algorithm

Identification and quantification method for chemical warfare agents (CWAs) was developed using a continuous and standalone type hazardous gas detection instrument (MKS AIRGARD® Air Analyzer), Fourier transform infra-red (FT-IR) spectroscopy system which uses a multi pass gas cell, a Stirling-cooled mercury cadmium telluride detector, and advanced data processing including an exponentially weighted moving background and chemical identification algorithm. Although FT-IR spectrum of sarin vapor prepared in ambient air included absorbance bands of carbon dioxide and water remaining due to incomplete background correction, characteristic absorbance bands were clearly observed in the fingerprint region (700–1400 cm−1) and around 2950 cm−1. n-Hexane was used not only as dissolving solvent for volatile CWAs but also as an interfering field matrix compound. The instrument provided a “GB” alarm against n-hexane (1320 mg/m3) vapor containing dilute sarin (more than 0.44 mg/m3). The height of the band peak at 1021 cm−1 increased proportionally with the concentration. Vapors of soman, tabun, cyclohexylsarin, VX and RVX, which were prepared in ambient air, provided correct alarms, and showed FT-IR spectra similar to that of sarin. The vapors of sulfur mustard, nitrogen mustard 3, Lewisite 1, cyanogen chloride and phosgene provided correct alarms with characteristic FT-IR features, which are different from those of nerve agents. The vapors of volatile CWAs except for VX and RVX provided correct alarm even in the presence of high level of n-hexane. The vapors of unregistered CWAs and mixture vapor of nerve agents were also examined.

Terahertz Time-Domain Spectroscopy of Low-Concentration N2O Using Long-Range Multipass Gas Cell

We developed a long-range multipass gas cell that extends the beam path to 18.61 m, for which a THz beam shows multiple reflections within a diameter of only 32 cm and a height of 54 cm. Due to the very long propagation THz beam path in the multipass gas cell, the absorbance and absorption coefficients of nitrous oxide can be measured very sensitively from 0.2 to 1.2 THz bandwidth. The gas concentration can be determined from the measured THz pulses for the absorption. As the gas concentration increased sequentially from 1.0% to 8.3% at atmospheric pressure, the absorbance lines also increased sequentially. The resulting absorptions and frequencies of transitions showed good agreement between experiment and calculations performed with the HITRAN database.

A Prototype of High-Precision Carbon Isotopic Ratio Sensing System for CO₂ Dissolved in Water

In natural gas hydrates' (NGHs) exploration, the carbon dioxide isotope abundance of dissolved gas in seawater should be accurately measured. However, in practical application, many challenges, such as the interference by organic compounds or the influence of the scatter distribution of NGHs, should be solved. In this study, a prototype of a midinfrared (MIR) CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> isotope abundance sensing system utilizing a simple linear optical structure is investigated to achieve a better precise measurements performance than current instruments. A self-designed temperature controlling system with a precision of 0.1 °C for the multipass gas cell (MPGC) is fabricated to guarantee the carbon isotope measuring precision. For <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> CO2 measurement, the minimum detection limit (MDL) is 48.4 ppbv with an integral time of 75 s. In addition, the precision of carbon isotope is low to 0.083 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> / <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> with an integration time of 121 s. A gas-liquid separator (GLS) combined with the sensing system is utilized to measure the carbon isotope ratio of the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The results validate the ability of the sensing system to measure continuously dissolved gases from water.

Silicon Multi-Pass Gas Cell for Chip-Scale Gas Analysis by Absorption Spectroscopy.

Semiconductor and micro-electromechanical system (MEMS) technologies have been already proved as strong solutions for producing miniaturized optical spectrometers, light sources and photodetectors. However, the implementation of optical absorption spectroscopy for in-situ gas analysis requires further integration of a gas cell using the same technologies towards full integration of a complete gas analysis system-on-chip. Here, we propose design guidelines and experimental validation of a gas cell fabricated using MEMS technology. The architecture is based on a circular multi-pass gas cell in a miniaturized form. Simulation results based on the proposed modeling scheme helps in determining the optimum dimensions of the gas cell, given the constraints of micro-fabrication. The carbon dioxide spectral signature is successfully measured using the proposed integrated multi-pass gas cell coupled with a MEMS-based spectrometer.

A Quantum Cascade Laser-Based Multi-Gas Sensor for Ambient Air Monitoring.

A quantum cascade laser-based sensor for ambient air monitoring is presented and five gases, affecting the air quality, can be quantified. The light sources are selected to measure CO, NO, NO2, N2O and SO2. The footprint of the measurement setup is designed to fit in two standard 19” rack (48 cm × 65 cm) with 4 height units (18 cm) whereas one is holding the optical components and the other one contains the electronics and data processing unit. The concentrations of the individual analytes are measured using 2f-Wavelength Modulation Spectroscopy (2f-WMS) and a commercially available multipass gas cell defines the optical path. In addition, CO can also be measured with a dispersion-based technique, which allows one to cover a wider concentration range than 2f-WMS. The performance of this prototype has been evaluated in the lab and detection limits in the range of 1ppbv have been achieved. Finally, the applicability of this prototype for ambient air monitoring is shown in a five-week measurement campaign in cooperation with the Municipal Department for Environmental Protection (MA 22) of Vienna, Austria.

Novel gas-phase sensing scheme using fiber-coupled off-axis integrated cavity output spectroscopy (FC-OA-ICOS) and cavity-reflected wavelength modulation spectroscopy (CR-WMS)

By feeding back the reflected light from the first cavity mirror to a single-/multi-pass gas cell via a multi-mode fiber, we demonstrated a novel gas-phase analytical scheme for methane (CH4) detection by combing fiber-coupled off-axis integrated cavity output spectroscopy (FC-OA-ICOS) and cavity-reflected wavelength modulation spectroscopy (CR-WMS). This scheme has an electrical module and two optical sensing modules which are connected through both single- and multi-mode optical fibers. Long-distance gas sensing application was conducted for verifying the analytical ability of the demonstrated technique exploiting the two fiber-coupled optical modules. A detection limit of 3 parts-per-million in volume (ppmv) for an 84 s averaging time and a precision of 56 ppmv for a 150 s averaging time were achieved using FC-OA-ICOS and CR-WMS, respectively. Two different CH4 measurement ranges were achieved in the sensor system with a wide dynamic range from ~15 ppmv to ~12% for CH4 detection. Field monitoring of CH4 leakage was performed for environmental analysis under a static and mobile mode using the wireless-controlled vehicle-mounted gas sensor. The proposed gas sensing scheme with fiber-coupled dual optical modules demonstrates a good potential for long-distance field CH4 measurements, especially for those in hazardous environment where in-situ human observation is impossible.

A Compact Circular Multipass Cell for Millimeter-Wave/Terahertz Gas Spectroscopy

Millimeter-wave/terahertz (mmW/THz) spectros-copy is a promising tool for gas sensing applications, such as breath analysis or the detection of toxic chemicals, which require compact portable systems. Long gas cells that are needed for high sensitivities are often bulky and limit the portability of the system. We present a compact mmW/THz circular multipass gas cell with an optical path length of 1.9 m and an outer diameter of only 21.5 cm. The beam is refocused at each internal reflection as a consequence of the large divergence of the mmW/THz beams. We determined the losses of the cell to about 3 dB around 250 GHz and demonstrated sensitive gas spectroscopy with a detection limit of 14 ppm/√Hz for acetaldehyde in a mixture with methanol.

The O2 far-infrared absorption spectrum between 50 and 170 cm-1

The oxygen absorption spectrum in the 50–170 cm-1 spectral range is studied at the AILES beam line of the SOLEIL synchrotron with a Fourier transform spectrometer equipped with a 151-m multipass gas cell. The spectrum recorded at room temperature (23.15 °C) with a pressure of 19.76 Torr is formed by weak pure rotational magnetic dipole transitions. Line parameters of 26 lines are derived and compared to literature values. In particular, measured line intensities confirm the 45 years-old previous values reported by Boreiko et al. (J. Quant. Spectrosc. Radiat. Transfer 32 (1984)109–117). The agreement with HITRAN intensities (within 1% level for the strongest lines) indicates that the 20% HITRAN error estimate was overly cautious: we show that the error is more likely within 2%.

Time-resolved characterization of non-thermal plasma-assisted photocatalytic removal of nitric oxide

We performed time-resolved characterization of plasma-photocatalytic removal of nitric oxide (NO) in a ceramic foam packing double dielectric barrier discharge reactor using mid-infrared laser absorption spectroscopy. Non-thermal plasma (NTP) was generated in the porous ceramic foam coated with mesoporous TiO2 thin film. Real-time NO monitoring was performed using a quantum cascade laser at 5.26 µm combined with a custom-designed multipass gas cell, leading to a sub-ppm detection limit at 0.1 s measurement time. By analyzing the feed gas of 90 ppm NO/1% O2 balanced in N2, the plasma treatment without TiO2 photocatalyst had no effect on NO removal when the discharge power was below 45 W. In comparison, the NTP-TiO2 system achieved an efficiency of 49% for NO removal even at the relatively low discharge power of 18 W. The synergy between NTP and TiO2 photocatalyst effectively promotes the NO removal at low plasma discharge powers. However, we also observed a negative effect of TiO2 photocatalyst on NO removal at a relatively high discharge power of 135 W.