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Author: David Wilson Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
This project was initially the continuation of a previous PhD students work. This changed slightly to incorporate the initial steps of development of a new system. However the main underlying focus was the absorption of infrared light by molecular gases using a still relatively new light source. This thesis will present the results of experimental work carried out during studies on the detection of gases and the nonlinear optical effects that arise from the absorption of light from a rapid frequency swept laser. A bench mounted two channel quantum cascade laser absorption spectrometer was used during experiments to observe and reduce nonlinear effects that arise from tuning the lasers during the absorption of light by several atmospherically important gases. These gases include the oxides of nitrogen (nitrous oxide, nitrogen dioxide and nitric oxide), methane and ammonia. The pulsed laser systems used as part of the spectrometer have also been put to use performing measurements on gaseous hydrocarbon combustion (methane and ethylene flames), to determine the feasibility of making measurements within the combustion zone of a jet engine and in conjunction with a continuous wave device during pump-probe experiments at the Chemistry Department of Oxford University. A portable four channel spectrometer was used at the beginning of the project to make measurements of the exhaust fumes of diesel powered vehicles. It will also cover the initial steps and tests performed in the early stages of development of a continuous wave quantum cascade laser based spectrometer for high speed detection of trace gases.
Author: David Wilson Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
This project was initially the continuation of a previous PhD students work. This changed slightly to incorporate the initial steps of development of a new system. However the main underlying focus was the absorption of infrared light by molecular gases using a still relatively new light source. This thesis will present the results of experimental work carried out during studies on the detection of gases and the nonlinear optical effects that arise from the absorption of light from a rapid frequency swept laser. A bench mounted two channel quantum cascade laser absorption spectrometer was used during experiments to observe and reduce nonlinear effects that arise from tuning the lasers during the absorption of light by several atmospherically important gases. These gases include the oxides of nitrogen (nitrous oxide, nitrogen dioxide and nitric oxide), methane and ammonia. The pulsed laser systems used as part of the spectrometer have also been put to use performing measurements on gaseous hydrocarbon combustion (methane and ethylene flames), to determine the feasibility of making measurements within the combustion zone of a jet engine and in conjunction with a continuous wave device during pump-probe experiments at the Chemistry Department of Oxford University. A portable four channel spectrometer was used at the beginning of the project to make measurements of the exhaust fumes of diesel powered vehicles. It will also cover the initial steps and tests performed in the early stages of development of a continuous wave quantum cascade laser based spectrometer for high speed detection of trace gases.
Author: Stefan Welzel Publisher: Logos Verlag Berlin GmbH ISBN: 3832523456 Category : Science Languages : en Pages : 198
Book Description
Infrared laser absorption spectroscopy (IRLAS) employing both tuneable diode and quantum cascade lasers (TDLs, QCLs) has been applied with both high sensitivity and high time resolution to plasma diagnostics and trace gas measurements. TDLAS combined with a conventional White type multiple pass cell was used to detect up to 13 constituent molecular species in low pressure Ar/H2/N2/O2 and Ar/CH4/N2/O2 microwave discharges, among them the main products such as H2O, NH3, NO and CO, HCN respectively. The hydroxyl radical has been measured in the mid infrared (MIR) spectral range in-situ in both plasmas yielding number densities of between 1011 ... 1012 cm-3. Strong indications of surface dominated formation of either NH3 or N2O and NO were found in the H2-N2-O2 system. In methane containing plasmas a transition between deposition and etching conditions and generally an incomplete oxidation of the precursor were observed. The application of QCLs for IRLAS under low pressure conditions employing the most common tuning approaches has been investigated in detail. A new method of analysing absorption features quantitatively when the rapid passage effect is present is proposed. If power saturation is negligible, integrating the undisturbed half of the line profile yields accurate number densities without calibrating the system. By means of a time resolved analysis of individual chirped QCL pulses the main reasons for increased effective laser line widths could be identified. Apart from the well-known frequency down chirp non-linear absorption phenomena and bandwidth limitations of the detection system may significantly degrade the performance and accuracy of inter pulse spectrometers. The minimum analogue bandwidth of the entire system should normally not fall below 250 MHz. QCLAS using pulsed lasers has been used for highly time resolved measurements in reactive plasmas for the first time enabling a time resolution down to about 100 ns to be achieved. A temperature increase of typically less than 50 K has been established for pulsed DC discharges containing Ar/N2 and traces of NO. The main NO production and depletion reactions have been identified from a comparison of model calculations and time resolved measurements in plasma pulses of up to 100 ms. Considerable NO struction is observed after 5 ... 10 ms due to the impact of N atoms. Finally, thermoelectrically cooled pulsed and continuous wave (cw) QCLs have been employed for high finesse cavity absorption spectroscopy in the MIR. Cavity ring down spectroscopy (CRDS) has been performed with pulsed QCLs and was found to be limited by the intrinsic frequency chirp of the laser suppressing an efficient intensity build-up inside the cavity. Consequently the accuracy and advantage of an absolute internal absorption calibration is not achievable. A room temperature cw QCL was used in a complementary cavity enhanced absorption spectroscopy (CEAS) configuration which was equipped with different cavities of up to 1.3 m length. This spectrometer yielded path lengths of up to 4 km and a noise equivalent absorption down to 4 x 10-8 cm-1Hz-1/2. The corresponding molecular concentration detection limit (e.g. for CH4, N2O and C2H2 at 1303 cm-1/7.66 Aem) was generally below 1 x 1010 cm-3 for 1 s integration times and one order of magnitude less for 30 s integration times. The main limiting factor for achieving even higher sensitivity is the residual mode noise of the cavity. Employing a 0.5 m long cavity the achieved sensitivity was good enough for the selective measurement of trace atmospheric constituents at 2.2 mbar.
Author: Yufei Ma Publisher: MDPI ISBN: 3039283987 Category : Technology & Engineering Languages : en Pages : 278
Book Description
Trace gas sensing technologies are widely used in many applications, such as environmental monitoring, life science, medical diagnostics, and planetary exploration. On the one hand, laser sources have developed greatly due to the rapid development of laser media and laser techniques in recent years. Some novel lasers such as solid-state, diode, and quantum cascade lasers have experienced significant progress. At present, laser wavelengths can cover the range from ultraviolet to terahertz, which could promote the development of laser gas sensing technologies significantly. On the other hand, some new gas sensing methods have appeared, such as photothermal spectroscopy and photoacoustic spectroscopy. Laser spectroscopy-based gas sensing techniques have the advantages of high sensitivity, non-invasiveness, and allowing in situ, real-time observation. Due to the rapid and recent developments in laser source as well as the great merits of laser spectroscopy-based gas sensing techniques, this book aims to provide an updated overview of the state-of-the-art laser gas sensing technologies.
Author: William M. Geiger Publisher: John Wiley & Sons ISBN: 1118642570 Category : Science Languages : en Pages : 309
Book Description
Explores the latest advances and applications of specialty and electronic gas analysis The semiconductor industry depends upon a broad range of instrumental techniques in order to detect and analyze impurities that may be present in specialty and electronic gases, including permanent gases, water vapor, reaction by-products, and metal species. Trace Analysis of Specialty and Electronic Gases draws together all the latest advances in analytical chemistry, providing researchers with both the theory and the operating principles of the full spectrum of instrumental techniques available for specialty and electronic gas analysis. Moreover, the book details the advantages and disadvantages of each technique, steering readers away from common pitfalls. Featuring contributions from leading analytical and industrial chemists, Trace Analysis of Specialty and Electronic Gases covers a wide range of practical industrial applications. The book begins with the historical development of gas analysis and then focuses on particular subjects or techniques such as: Metals sampling and ICP-MS analysis Improvements in FTIR spectroscopy Water vapor analysis techniques New infrared laser absorption spectroscopy approaches GC/MS, GC/AED, and GC-ICP-MS techniques Gas chromatography columns Atmospheric pressure ionization mass spectrometry Lastly, the book examines gas mixtures and standards that are critical for instrument calibration. There are also two appendices offering information on fittings and material compatibility. With its thorough review of the literature and step-by-step guidance, Trace Analysis of Specialty and Electronic Gases enables researchers to take full advantage of the latest advances in gas analysis. Although the book's focus is the semiconductor and electronics industry, analytical chemists in other industries facing challenges with such issues as detection selectivity and sensitivity, matrix gas interference, and materials compatibility will also discover plenty of useful analytical approaches and techniques.
Author: Publisher: ISBN: Category : Languages : en Pages : 43
Book Description
We have developed a compact, robust, atmospheric trace gas detector based on mid-infrared absorption spectroscopy using pulsed quantum cascade (QC) lasers. The spectrometer is suitable for airborne measurements of ammonia, nitric acid, formaldehyde, formic acid, methane, nitrous oxide, carbon monoxide, nitrogen dioxide and other gases that have line-resolved absorption spectra in the mid-infrared spectral region. The QC laser light source operates near room temperature with thermal electric cooling instead of liquid nitrogen which has been previously required for semiconductor lasers in the mid-infrared spectral region. The QC lasers have sufficient output power so that thermal electric cooled detectors may be used in many applications with lower precision requirements. The instrument developed in this program has been used in several field campaigns from both the Aerodyne Mobile Laboratory and from the NOAA WP3 aircraft. The Phase II program has resulted in more than 10 archival publications describing the technology and its applications. Over 12 instruments based on this design have been sold to research groups in Europe and the United States making the program both a commercial as well as a technological success. Anticipated Benefits The development of a sensitive, cryogen-free, mid-infrared absorption method for atmospheric trace gas detection will have wide benefits for atmospheric and environmental research and broader potential commercial applications in areas such as medical diagnostic and industrial process monitoring of gaseous compounds. Examples include air pollution monitoring, breath analysis, combustion exhaust diagnostics, and plasma diagnostics for semi-conductor fabrication. The substitution of near-room temperature QC lasers for cryogenic lead salt TDLs and the resulting simplifications in instrument design and operation will greatly expand the range of applications.
Author: Weidong Chen Publisher: Elsevier ISBN: 0128156899 Category : Science Languages : en Pages : 634
Book Description
Advances in Spectroscopic Monitoring of the Atmosphere provides a comprehensive overview of cutting-edge technologies and monitoring applications. Concepts are illustrated by numerous examples with information on spectroscopic techniques and applications widely distributed throughout the text. This information is important for researchers to gain an overview of recent developments in the field and make informed selections among the most suitable techniques. This volume also provides information that will allow researchers to explore implementing and developing new diagnostic tools or new approaches for trace gas and aerosol sensing themselves. Advances in Spectroscopic Monitoring of the Atmosphere covers advanced and newly emerging spectroscopic techniques for optical metrology of gases and particles in the atmosphere. This book will be a valuable reference for atmospheric scientists, including those whose focus is applying the methods to atmospheric studies, and those who develop instrumentation. It will also serve as a useful introduction to researchers entering the field and provide relevant examples to researchers and students developing and applying optical sensors for a variety of other scientific, technical, and industrial uses. - Overview of new applications including remote sensing by UAV, laser heterodyne radiometry, dual comb spectroscopy, and more - Features in-situ observations and measurements for real-world data - Includes content on leading edge optical sensors
Author: David Wilson
Author: David Wilson
Author: Tomás Henrique Passos Pinto
Author: Stefan Welzel
Author: Michael Telfer McCulloch
Author: Jagadeeshwari Manne
Author: Yufei Ma
Author: William M. Geiger
Author: 
Author: Christina Rachel Young
Author: Weidong Chen