Off-resonant photoacoustic spectroscopy for analysis of multicomponent gas mixtures at high concentrations using broadband vibrational overtones of individual gas species
TL;DR: The broadband photoacoustic spectroscopy technique is proposed and demonstrated for measurement of CH4, CO2, and H2O vapor in the 1.6 to 2.0 μm wavelength region and exhibits a wide concentration measurement range of parts per billion by volume to 100%.
Abstract: The broadband photoacoustic spectroscopy (PAS) technique is proposed and demonstrated for measurement of CH4, CO2, and H2O vapor in the 1.6 to 2.0 μm wavelength region. The wide spectrum of a supercontinuum light source is used to cover broadband absorption bands of multiple gas species. This sensor works in the off-resonant frequency of the designed photoacoustic cell and exhibits a wide concentration measurement range of parts per billion by volume (ppb-v) to 100%. The PAS sensor is further tested in real time by measuring the concentration of CO2, CH4, and H2O vapor in biogas plants.
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TL;DR: While mid-infrared point-of-care instrumentation promises high sensitivity and inherent molecular selectivity, the lack of standardization of the various techniques has to be overcome for translating these techniques into more widespread real-time clinical use.
Abstract: Human exhaled breath consists of more than 3000 volatile organic compounds, many of which are relevant biomarkers for various diseases. Although gas chromatography has been the gold standard for volatile organic compound (VOC) detection in exhaled breath, recent developments in mid-infrared (MIR) laser spectroscopy have led to the promise of compact point-of-care (POC) optical instruments enabling even single breath diagnostics. In this review, we discuss the evolution of MIR sensing technologies with a special focus on photoacoustic spectroscopy, and its application in exhaled breath biomarker detection. While mid-infrared point-of-care instrumentation promises high sensitivity and inherent molecular selectivity, the lack of standardization of the various techniques has to be overcome for translating these techniques into more widespread real-time clinical use.
59 citations
TL;DR: An off-resonance broadband photoacoustic spectroscopy (PAS) technique with a supercontinuum laser (SCL) in the near-infrared range is demonstrated for biogas measurements with different biomass matrices, showing the suitability of the PAS sensor to be employed in a fully operational large scaleBiogas plant for online monitoring.
Abstract: An off-resonance broadband photoacoustic spectroscopy (PAS) technique with a supercontinuum laser (SCL) in the near-infrared range is demonstrated for biogas measurements with different biomass mat...
10 citations
TL;DR: A two-component gas sensor in quartz-enhanced photoacoustic spectroscopy based on time-division multiplexing (TDM) technology of a distributed-feedback (DFB) laser driver current was proposed and experimentally demonstrated.
Abstract: A two-component gas sensor in quartz-enhanced photoacoustic spectroscopy based on time-division multiplexing (TDM) technology of a distributed-feedback (DFB) laser driver current was proposed and experimentally demonstrated. The quartz tuning-fork-based photoacoustic spectroscopy (PAS) cell configuration with two optical collimators and two acoustic microresonators was designed to detect the second-harmonic (${2}f$2f) PAS signal. The two optical collimators guaranteed that the two laser beams would inject the PAS cell conveniently, providing higher power input than a 3 dB optical fiber coupler. Two-component gas sensing was achieved by the TDM of the DFB laser driver current. We used this two-component gas sensing technique to detect acetylene (${{\rm C}_2}{{\rm H}_2}$C2H2) at 1532.83 nm and methane (${{\rm CH}_4}$CH4) at 1653.722 nm. The ${{\rm C}_2}{{\rm H}_2}$C2H2 and ${{\rm CH}_4}$CH4 detection was achieved at a 2.4 s interval. The minimum detection limits of 1 ppmv for ${{\rm C}_2}{{\rm H}_2}$C2H2 and 13.14 ppmv for ${{\rm CH}_4}$CH4 were obtained, and the linear responses reached were 0.99968 and 0.99652 for ${{\rm C}_2}{{\rm H}_2}$C2H2 and ${{\rm CH}_4}$CH4, respectively. Moreover, the continuous monitoring of ${{\rm CH}_4}$CH4 and ${{\rm C}_2}{{\rm H}_2}$C2H2 for 40 min showed a good stability. The TDM technology of the DFB laser driver current would play an important role on the multi-component detection.
8 citations
TL;DR: In this article, a compact and portable quartz-enhanced photoacoustic spectroscopy gas sensor was developed for four-component gas detection using two off-beam acoustic microresonators (AMRs).
Abstract: A compact and portable quartz-enhanced photoacoustic spectroscopy gas sensor was developed for four-component gas detection using two off-beam acoustic microresonators (AMRs). The two AMRs were placed in parallel on opposing sides of a quartz tuning fork (QTF) for photoacoustic signal enhancement. Four distributed feedback (DFB) lasers were connected to the four ends of the two off-beam AMRs using a fiber collimator for photoacoustic signal excitation. Four-component gas sensing was achieved via time-division multiplexing of the DFB laser driver currents. The four-component gas sensing scheme was used to detect acetylene (C2H2) at 1532.83 nm, methane (CH4) at 1653.722 nm, water vapor (H2O) at 1368.597 nm and carbon dioxide (CO2) at 1577.787 nm for feasibility testing. Minimum detection limits of 3.6 ppmv for C2H2, 34.71 ppmv for CH4, 1.09 ppmv for H2O, and 341.18 ppmv for CO2 were obtained, and the linear responses reached 0.9982, 0.9969, 0.99843 and 0.99591 for C2H2, CH4, H2O and CO2, respectively, at 1.5 s intervals.
2 citations
Cites methods from "Off-resonant photoacoustic spectros..."
...0 μm to detect CH4, CO2, and H2O via the broadband PAS technique [27]....
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TL;DR: In this paper , photoacoustic spectroscopy (PAS) is used for the detection of trace gases and isotopologic analysis of short-chain hydrocarbons such as methane, ethane or propane.
Abstract: Photoacoustic spectroscopy (PAS) is typically used for the detection of trace gases. In this way, mixtures of short-chain hydrocarbons such as methane, ethane or propane can be analyzed with detection limits in the range of parts per million (ppm) or parts per billion (ppb) or even below. However, there are a number of applications where highly concentrated mixtures need to be analyzed. In some cases even the isotopologic composition of certain hydrocarbons needs to be determined. Examples can be found in natural gas production and planetary research. We present PAS-based isotopologic analyses of two digit percentage-level methane concentrations in nitrogen. The investigation allows conclusions to be drawn about the extent to which PAS is suitable for an isotopologic analysis of undiluted natural gas-like mixtures.
2 citations
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TL;DR: In this paper, the theoretical and practical aspects of high-Q and low-Q resonators and their integration into complete photoacoustic detection systems for trace gas monitoring and metrology are covered in detail.
Abstract: The application of different types of acoustic resonators such as pipes, cylinders, and spheres in photoacoustics is considered. This includes a discussion of the fundamental properties of these resonant cavities. Modulated and pulsed laser excitation of acoustic modes is discussed. The theoretical and practical aspects of high-Q and low-Q resonators and their integration into complete photoacoustic detection systems for trace gas monitoring and metrology are covered in detail. The characteristics of the available laser sources and the performance of the photoacoustic resonators, such as signal amplification, are discussed. Setup properties and noise features are considered in detail. This review is intended to give newcomers the information needed to design and construct state-of-the-art photoacoustic detectors for specific purposes such as trace gas analysis, spectroscopy, and metrology.
621 citations
TL;DR: In this article, the authors extended the theory of photoacoustic effect to include the contribution of mechanical vibration of the sample and solved equations for thermal and acoustic waves in both sample and gas.
Abstract: The theory of the photoacoustic effect is extended to include the contribution of mechanical vibration of the sample. Coupled equations for thermal and acoustic waves are solved in both sample and gas. It is shown that the pressure signal in the gas may be significantly affected by acoustic coupling in the sample, and experimental confirmation of this extended theory is given. The results of the fully coupled treatment are shown to be accurately reproduced by an extension of the Rosencwaig piston model: the pistonlike motion of the gas boundary layer adjoining the sample is superimposed on the mechanical vibration of the sample surface to give a composite piston displacement which then produces the pressure signal in the gas. The composite‐piston model provides relatively simple algebraic results applicable to many cases of physical interest.
451 citations
TL;DR: TOLAS has become an accepted technique in the process industries for difficult measurement tasks, because it is compatible with high temperatures, pressures, dust levels and corrosive media as discussed by the authors. And TOLAS is used widely for continuous emission monitoring and process control with over 1,000 field instruments worldwide.
Abstract: The availability of new lasers in the nearand mid infrared spectral region has led to the development of sensors for gas measurements that are now applied extensively in the process industries. Based on tunable diode laser absorption spectroscopy (TOLAS) molecules like O2, CH* H2O, CO, CO2, NH3, HC1 and HF can be detected in-situ with high selectivity and sensitivity in continuous, real time operation. Using sensitive detection techniques like wavelength modulation spectroscopy (WMS), often low ppb and ppm concentration measurements with Is integration time are feasible. Detection limits can be improved by using extractive sampling and a long multi-pass cell. TOLAS has become an accepted technique in the process industries for difficult measurement tasks, because it is compatible with high temperatures, pressures, dust levels and corrosive media. Gas concentrations, temperatures, velocities and pressures can be determined. TOLAS is used widely for continuous emission monitoring and process control with over 1,000 field instruments worldwide. In this article, after an introduction to the basics of TOLAS, several interesting applications and installations in various process industrial units with some examples from other industries are reviewed.
247 citations
TL;DR: This OB-QEPAS configuration not only allows for use of larger excitation optical beams and facilitating optical alignment but also provides higher enhancement of photoacoustic signals than previously published results based on the common on-beam QEPAS under the same experimental conditions.
Abstract: An off-beam (OB) detection approach is suggested and experimentally investigated and optimized for quartz-enhanced photoacoustic spectroscopy (QEPAS). This OB-QEPAS configuration, very simple in assembly, not only allows for use of larger excitation optical beams and facilitating optical alignment but also provides higher enhancement of photoacoustic signals than previously published results based on the common on-beam QEPAS under the same experimental conditions. A normalized noise equivalent absorption coefficient (1σ) of 5.9×10−9 cm−1W/Hz1/2 was obtained for water vapor detection at normal atmospheric pressure.
194 citations
TL;DR: In this article, the performance of various spectroscopic systems with different lasers (gas lasers, nonlinear optical sources like optical parametric oscillators and difference frequency generation, near-infrared external cavity diode lasers, quantum cascade lasers) and different detection schemes (photoacoustic, multipass transmission, cavity ringdown) are discussed and illustrated with examples from various areas.
Abstract: Trace gas sensing systems have to meet several requirements like high detection sensitivity and selectivity, multicomponent capability, field suitability, etc. In this respect devices based on tunable lasers combined with appropriate detection schemes are attracting great interest. This report reviews recent developments demonstrating the potential of such systems. The performance of various spectroscopic systems with different lasers (gas lasers, nonlinear optical sources like optical parametric oscillators and difference frequency generation, near-infrared external cavity diode lasers, quantum cascade lasers) and different detection schemes (photoacoustic, multipass transmission, cavity ringdown) is discussed and illustrated with examples from various areas. Applications include laboratory analyses of multicomponent samples with isotopic selectivity, field measurements in ambient urban and rural air or even at volcanic sites, as well as investigations in the area of biology and medical diagnostics.
161 citations