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Kwaśny M, Bombalska A. Optical Methods of Methane Detection. SENSORS (BASEL, SWITZERLAND) 2023; 23:2834. [PMID: 36905038 PMCID: PMC10007260 DOI: 10.3390/s23052834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 03/02/2023] [Accepted: 03/02/2023] [Indexed: 06/18/2023]
Abstract
Methane is the most frequently analyzed gas with different concentrations ranging from single ppm or ppb to 100%. There are a wide range of applications for gas sensors including urban uses, industrial uses, rural measurements, and environment monitoring. The most important applications include the measurement of anthropogenic greenhouse gases in the atmosphere and methane leak detection. In this review, we discuss common optical methods used for detecting methane such as non-dispersive infrared (NIR) technology, direct tunable diode spectroscopy (TDLS), cavity ring-down spectroscopy (CRDS), cavity-enhanced absorption spectroscopy (CEAS), lidar techniques, and laser photoacoustic spectroscopy. We also present our own designs of laser methane analyzers for various applications (DIAL, TDLS, NIR).
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Widely-Tunable Quantum Cascade-Based Sources for the Development of Optical Gas Sensors. SENSORS 2020; 20:s20226650. [PMID: 33233578 PMCID: PMC7699741 DOI: 10.3390/s20226650] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 11/16/2020] [Accepted: 11/16/2020] [Indexed: 01/22/2023]
Abstract
Spectroscopic techniques based on Distributed FeedBack (DFB) Quantum Cascade Lasers (QCL) provide good results for gas detection in the mid-infrared region in terms of sensibility and selectivity. The main limitation is the QCL relatively low tuning range (~10 cm-1) that prevents from monitoring complex species with broad absorption spectra in the infrared region or performing multi-gas sensing. To obtain a wider tuning range, the first solution presented in this paper consists of the use of a DFB QCL array. Tuning ranges from 1335 to 1387 cm-1 and from 2190 to 2220 cm-1 have been demonstrated. A more common technique that will be presented in a second part is to implement a Fabry-Perot QCL chip in an external-cavity (EC) system so that the laser could be tuned on its whole gain curve. The use of an EC system also allows to perform Intra-Cavity Laser Absorption Spectroscopy, where the gas sample is placed within the laser resonator. Moreover, a technique only using the QCL compliance voltage technique can be used to retrieve the spectrum of the gas inside the cavity, thus no detector outside the cavity is needed. Finally, a specific scheme using an EC coherent QCL array can be developed. All these widely-tunable Quantum Cascade-based sources can be used to demonstrate the development of optical gas sensors.
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Gao G, Zhang T, Zhang G, Liu X, Cai T. Simultaneous and interference-free measurements of temperature and C 2H 4 concentration using a single tunable diode laser at 1.62 µm. OPTICS EXPRESS 2019; 27:17887-17904. [PMID: 31252741 DOI: 10.1364/oe.27.017887] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Accepted: 05/31/2019] [Indexed: 06/09/2023]
Abstract
In the tunable diode laser absorption spectroscopy-based diagnostics, the absorption of the measured target species may be influenced by the interference absorption from other vapor-phase species and the extinction from particles and liquid droplets, especially at high temperatures and pressures. Here, we report the first application (to our knowledge) of a differential absorption diagnostic for interference-free, simultaneous measurement of temperature and ethylene concentration using a single distributed-feedback diode laser near 1.62 μm. According to the detailed study of the C2H4 spectra in this region, two wavelength pairs are chosen to measure the temperature based on six selection criteria. C2H4 concentration is measured by one of the selected wavelength pairs with higher differential absorption. To validate the developed system, experiments are performed in a well-controlled heated static cell at a range of temperatures (300-900 K) and pressures (1-6 atm). The measurement accuracies for temperature and ethylene concentration are 1.83% and 1.65%, respectively, over the considered ranges. The precision, stability, and detection limit are also analyzed to validate the system's performance. This system can potentially be applied in a variety of combustion applications.
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Abstract
Until very recently, handheld spectrometers were the domain of major analytical and security instrument companies, with turnkey analyzers using spectroscopic techniques from X-ray fluorescence (XRF) for elemental analysis (metals), to Raman, mid-infrared, and near-infrared (NIR) for molecular analysis (mostly organics). However, the past few years have seen rapid changes in this landscape with the introduction of handheld laser-induced breakdown spectroscopy (LIBS), smartphone spectroscopy focusing on medical diagnostics for low-resource areas, commercial engines that a variety of companies can build up into products, hyphenated or dual technology instruments, low-cost visible-shortwave NIR instruments selling directly to the public, and, most recently, portable hyperspectral imaging instruments. Successful handheld instruments are designed to give answers to non-scientist operators; therefore, their developers have put extensive resources into reliable identification algorithms, spectroscopic libraries or databases, and qualitative and quantitative calibrations. As spectroscopic instruments become smaller and lower cost, "engines" have emerged, leading to the possibility of being incorporated in consumer devices and smart appliances, part of the Internet of Things (IOT). This review outlines the technologies used in portable spectroscopy, discusses their applications, both qualitative and quantitative, and how instrument developers and vendors have approached giving actionable answers to non-scientists. It outlines concerns on crowdsourced data, especially for heterogeneous samples, and finally looks towards the future in areas like IOT, emerging technologies for instruments, and portable hyphenated and hyperspectral instruments.
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Wang Z, Geng J, Ren W. Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) Detection of the ν 7 Band of Ethylene at Low Pressure with CO 2 Interference Analysis. APPLIED SPECTROSCOPY 2017; 71:1834-1841. [PMID: 28145742 DOI: 10.1177/0003702817690406] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Ethylene (C2H4) was detected using quartz-enhanced photoacoustic spectroscopy (QEPAS) at 10.5 µm with a continuous wave, distributed-feedback quantum cascade laser as the light source. The QEPAS sensor was operated at low pressures (≤200 torr) to eliminate the cross-talk spectral interference between C2H4 and CO2, a major interfering species in practical applications. The sensor was calibrated to show a good linear response to C2H4 concentration and the Allan deviation analysis demonstrated a minimum detection limit of 8 ppb at an integration time of 90 s. Although no spectral overlap between C2H4 and CO2 was confirmed at the pressure ≤200 torr by the direct absorption measurement using a 28-m multipass cell, we observed the apparent influence of the CO2 addition to the C2H4/N2 mixture on the photoacoustic signal of C2H4. An energy transfer model involving the vibration-vibration (VV) and vibration-translation (VT) transitions in the C2H4-CO2-N2 system was constructed to interpret the experimental data. Additionally, the vibrational relaxation times of C2H4 were obtained based on the QEPAS technique and the energy transfer model, which were in good agreement with the previous studies.
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Affiliation(s)
- Zhen Wang
- Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, New Territories, Hong Kong
| | - Jian Geng
- Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, New Territories, Hong Kong
| | - Wei Ren
- Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, New Territories, Hong Kong
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6
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Wang Z, Li Z, Ren W. Quartz-enhanced photoacoustic detection of ethylene using a 10.5 μm quantum cascade laser. OPTICS EXPRESS 2016; 24:4143-4154. [PMID: 26907064 DOI: 10.1364/oe.24.004143] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor has been developed for the sensitive detection of ethylene (C2H4) at 10.5 µm using a continuous-wave distributed-feedback quantum cascade laser. At this long-wavelength infrared, the key acoustic elements of quartz tuning fork and micro-resonators were optimized to improve the detection signal-to-noise ratio by a factor of >4. The sensor calibration demonstrated an excellent linear response (R2>0.999) to C2H4 concentration at the selected operating pressure of 500 and 760 Torr. With a minimum detection limit of 50 parts per billion (ppb) achieved at an averaging time of 70 s, the sensor has been deployed for measuring the C2H4 efflux during the respiration of biological samples in an agronomic environment.
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Janassek P, Hartmann S, Molitor A, Michel F, Elsäßer W. Investigations of the polarization behavior of quantum cascade lasers by Stokes parameters. OPTICS LETTERS 2016; 41:305-308. [PMID: 26766700 DOI: 10.1364/ol.41.000305] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We experimentally investigate the full polarization behavior of mid-infrared emitting quantum cascade lasers (QCLs) in terms of measuring the complete Stokes parameters, instead of only projecting them on a linear polarization basis. We demonstrate that besides the pre-dominant linear TM polarization of the emitted light as governed by the selection rules of the intersubband transition, small non-TM contributions, e.g., circularly polarized light, are present reflecting the birefringent behavior of the semiconductor quantum well waveguide. Surprisingly unique is the persistence of these polarization properties well below laser threshold. These investigations give further insight into understanding, manipulating, and exploiting the polarization properties of QCLs, both from a laser point of view and with respect toward applications.
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Aziz MSI, Orr-Ewing AJ. Development and application of an optical sensor for ethene in ambient air using near infra-red cavity ring down spectroscopy and sample preconcentration. ACTA ACUST UNITED AC 2012; 14:3094-100. [DOI: 10.1039/c2em30801k] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Yuanyuan T, Wenqing L, Ruifeng K, Jianguo L, Yabai H, Yujun Z, Zhenyu X, Jun R, Hui G. Measurements of NO and CO in Shanghai urban atmosphere by using quantum cascade lasers. OPTICS EXPRESS 2011; 19:20224-20232. [PMID: 21997033 DOI: 10.1364/oe.19.020224] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Nitric oxide (NO) and carbon monoxide (CO) in Shanghai urban atmosphere have been measured during the EXPO 2010 by an optical trace gas monitoring system based on room-temperature pulsed quantum cascade lasers (QCL). The results showed obvious diurnal variation in their concentrations. A great correlation was found by analyzing the diurnal variation, indicating common emission sources for both NO and CO. However analysis of the data from street canyon measurements showed that on a vehicle-by-vehicle basis NO emissions correlated only weakly with CO emissions. A possible explanation to this issue has been given.
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Affiliation(s)
- Tang Yuanyuan
- Key Lab. of Environmental Optics & Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
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Duxbury G, Hay KG, Langford N, Johnson MP, Black JD. Real-time diagnostics of a jet engine exhaust using an intra-pulse quantum cascade laser spectrometer. Mol Phys 2011. [DOI: 10.1080/00268976.2011.610367] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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McCulloch MT, Duxbury G, Langford N. Observation of saturation and rapid passage signals in the 10.25 micron spectrum of ethylene using a frequency chirped quantum cascade laser. Mol Phys 2010. [DOI: 10.1080/00268970600857651] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Mothé G, Castro M, Sthel M, Lima G, Brasil L, Campos L, Rocha A, Vargas H. Detection of greenhouse gas precursors from diesel engines using electrochemical and photoacoustic sensors. SENSORS (BASEL, SWITZERLAND) 2010; 10:9726-41. [PMID: 22163437 PMCID: PMC3230984 DOI: 10.3390/s101109726] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Revised: 09/09/2010] [Accepted: 10/29/2010] [Indexed: 11/27/2022]
Abstract
Atmospheric pollution is one of the worst threats to modern society. The consequences derived from different forms of atmospheric pollution vary from the local to the global scale, with deep impacts on climate, environment and human health. Several gaseous pollutants, even when present in trace concentrations, play a fundamental role in important processes that occur in atmosphere. Phenomena such as global warming, photochemical smog formation, acid rain and the depletion of the stratospheric ozone layer are strongly related to the increased concentration of certain gaseous species in the atmosphere. The transport sector significantly produces atmospheric pollution, mainly when diesel oil is used as fuel. Therefore, new methodologies based on selective and sensitive gas detection schemes must be developed in order to detect and monitor pollutant gases from this source. In this work, CO(2) Laser Photoacoustic Spectroscopy was used to evaluate ethylene emissions and electrochemical analyzers were used to evaluate the emissions of CO, NO(x) and SO(2) from the exhaust of diesel powered vehicles (rural diesel with 5% of biodiesel, in this paper called only diesel) at different engine rotation speeds. Concentrations in the range 6 to 45 ppmV for ethylene, 109 to 1,231 ppmV for carbon monoxide, 75 to 868 ppmV for nitrogen oxides and 3 to 354 ppmV for sulfur dioxide were obtained. The results indicate that the detection techniques used were sufficiently selective and sensitive to detect the gaseous species mentioned above in the ppmV range.
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Affiliation(s)
- Geórgia Mothé
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
| | - Maria Castro
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
| | - Marcelo Sthel
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
| | - Guilherme Lima
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
| | - Laisa Brasil
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
| | - Layse Campos
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
| | - Aline Rocha
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
| | - Helion Vargas
- Laboratório de Ciências Físicas LCFIS–Universidade Estadual do Norte Fluminense UENF, Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brasil; E-Mails: (G.M.); (M.S.); (G.L.); (L.B.); (L.C.); (A.R.) (H.V.)
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Northern JH, Ritchie GAD, Smakman EP, van Helden JH, Cockburn J, Duxbury G. Rapid passage signals induced by chirped quantum cascade laser radiation: K state dependent-delay effects in the nu2 band of NH3. OPTICS LETTERS 2010; 35:2750-2752. [PMID: 20717445 DOI: 10.1364/ol.35.002750] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
In this Letter, a 10 microm quantum cascade laser operating in the intrapulse mode is used observe rapid passage (RP) effects within a 40 cm single-pass gas cell containing low pressures of NH(3). The laser tuning range allows the rotational states J=2 with K=0, 1, and 2 to be probed. We show that the RP structures change as a function of optical density and that the magnitude of the delay in the switch from absorption to emission as a function of increased gas pressure is dependent upon the initial value of K. These measurements are qualitatively well modeled using the Maxwell-Bloch equations.
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Affiliation(s)
- J H Northern
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QZ, UK
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Schneider H, Liu HC, Winnerl S, Song CY, Walther M, Helm M. Terahertz two-photon quantum well infrared photodetector. OPTICS EXPRESS 2009; 17:12279-12284. [PMID: 19654629 DOI: 10.1364/oe.17.012279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A two-photon detector based on intersubband transitions in GaAs/AlGaAs quantum wells operating in the Terahertz regime below the Reststrahlenband is reported. Resonantly enhanced optical nonlinearities enables sensitive quadratic detection at pJ pulse energies. We demonstrate its use in a quadratic autocorrelator for far-infrared picosecond pulses at around 7 THz.
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Affiliation(s)
- H Schneider
- Forschungszentrum Dresden Rossendorf, Institute of Ion Beam Physics and Materials Research, P O Box 510119, D-01314 Dresden, Germany.
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Lytkine A, Manne J, Jäger W, Tulip J. Characterization of a 10.3-microm pulsed DFB quantum cascade laser. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2006; 63:947-51. [PMID: 16503190 DOI: 10.1016/j.saa.2005.11.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2005] [Revised: 11/08/2005] [Accepted: 11/09/2005] [Indexed: 05/06/2023]
Abstract
We have measured the output parameters of a 10.3-microm pulsed distributed-feedback (DFB) quantum cascade (QC) laser manufactured by Alpes Lasers and intended for high-sensitivity detection of ammonia and ethylene. The laser beam was collimated with an AR-coated aspheric ZnSe lens with focal length of 11.6mm and clear aperture of 16.5mm. Near- and far-field distributions of the laser emission were recorded with an infrared imaging camera. The fast-and slow-axis laser beam divergences were measured to be 1.2 and 1.4 mrad (FWHM), respectively. The divergence was found to be increasing with injection current. An air-spaced Fabry-Perot interferometer with free spectral range of 0.05 cm(-1) was used to measure the frequency tuning rates of the laser. The laser was tuned by either heat sink temperature, injection current or pulse repetition rate with rates of approximately -8 x 10(-2)cm(-1)K(-1), -7 x 10(-2)cm(-1)A(-1) and -9 x 10(-4)cm(-1)kHz(-1), respectively. The laser frequency decreased linearly with a rate of 10(-2)cm(-1)ns(-1) ( approximately 300 MHzns(-1)) for laser pulses varied from 10 to 50 ns, and the frequency chirp rate was found to decrease for longer laser pulses.
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Affiliation(s)
- A Lytkine
- Electrical and Computer Engineering Department, University of Alberta, 9107-116 Street, Edmonton, AB, Canada T6G 2V4.
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Cheesman A, Smith JA, Ashfold MNR, Langford N, Wright S, Duxbury G. Application of a Quantum Cascade Laser for Time-Resolved, in Situ Probing of CH4/H2 and C2H2/H2 Gas Mixtures during Microwave Plasma Enhanced Chemical Vapor Deposition of Diamond. J Phys Chem A 2006; 110:2821-8. [PMID: 16494395 DOI: 10.1021/jp056622u] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
First illustrations of the utility of pulsed quantum cascade lasers for in situ probing of the chemistry prevailing in microwave plasma activated hydrocarbon/Ar/H2 gas mixtures used for diamond thin film growth are reported. CH4 and C2H2 molecules, and their interconversion, have been monitored by line-of-sight single pass absorption methods, as a function of process conditions (e.g., choice of input hydrocarbon (CH4 or C2H2), hydrocarbon mole fraction, total gas pressure, and applied microwave power). The observed trends can be rationalized, qualitatively, within the framework of the previously reported modeling of the gas-phase chemistry prevailing in hot filament activated hydrocarbon/H2 gas mixtures (Ashfold et al. Phys. Chem. Chem. Phys. 2001, 3, 3471). Column densities of vibrationally excited C2H2(v5=1) molecules at low input carbon fractions are shown to be far higher than expected on the basis of local thermodynamic equilibrium. The presence of vibrationally excited C2H2 molecules (C2H2(double dagger)) can be attributed to the exothermicity of the C2H3 + H <==> C2H2 + H2 elementary reaction within the overall multistep CH4 --> C2H2 conversion. Diagnostic methods that sample just C2H2(v=0) molecules thus run the risk of underestimating total C2H2 column densities in hydrocarbon/H2 mixtures operated under conditions where the production rate of C2H2(double dagger) molecules exceeds their vibrational relaxation (and thermal equilibration) rates.
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Affiliation(s)
- A Cheesman
- School of Chemistry, University of Bristol, Bristol, United Kingdom BS8 1TS
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Lindley RE, Pradhan M, Orr-Ewing AJ. Measuring acetylene concentrations using a frequency chirped continuous wave diode laser operating in the near infrared. Analyst 2006; 131:731-8. [PMID: 16732361 DOI: 10.1039/b600506c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two frequency chirped continuous wave diode lasers operating in the near infrared (IR) at wavelengths of lambda approximately 1.535 microm and lambda approximately 1.520 microm have been used to measure acetylene concentrations using the P(17) and R(9) rotational lines of the (nu1 + nu3) vibrational combination band. The diode lasers were frequency chirped by applying an electrical current pulse to the laser driver at a repetition rate of greater than 1 kHz. As the laser is operated at high repetition rates, more than 1000 spectra per second can, in principle, be acquired and summed, allowing fast accumulation of data, rapid averaging and consequent improvement of the signal to noise ratio and detection limit. Experiments were performed using a single-pass cell with a path length of 16.4 cm, and also an astigmatic multi-pass absorption cell aligned to give a path length of 56 m. Detection limits corresponding to minimum detectable absorption coefficients, alpha(min), of 5.6 x 10(-5) and 7.8 x 10(-8) cm(-1), respectively, were obtained over a 4 s detection bandwidth. These detection limits would correspond to mixing ratios of 21 parts per million by volume (ppmv) and 59 parts per billion by volume (ppbv) of acetylene at 1 atm in air, with the deleterious effects of pressure broadening accounted for. The single-pass cell was used to perform breakthrough volume (BTV) experiments for the low volume adsorbent traps used to pre-concentrate organic compounds in air, taking advantage of the capability of the system to measure concentrations in real time.
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Affiliation(s)
- Ruth E Lindley
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS
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Duxbury G, Langford N, McCulloch MT, Wright S. Quantum cascade semiconductor infrared and far-infrared lasers: from trace gas sensing to non-linear optics. Chem Soc Rev 2005; 34:921-34. [PMID: 16239994 DOI: 10.1039/b400914m] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The Quantum cascade (QC) laser is an entirely new type of semiconductor device in which the laser wavelength depends on the band-gap engineering. It can be made to operate over a much larger range than lead salt lasers, covering significant parts of both the infrared and submillimetre regions, and with higher output power. In this tutorial review we survey some of the applications of these new lasers, which range from trace gas detection for atmospheric or medical purposes to sub-Doppler and time dependent non-linear spectroscopy.
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Affiliation(s)
- Geoffrey Duxbury
- Department of Physics, University of Strathclyde, John Anderson Building, 107 Rottenrow, Glasgow, UK G4 0NG
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