<div class="csl-bib-body">
<div class="csl-entry">Waclawek, J. P. (2017). <i>Development of mid-infrared laser based photoacoustic and photothermal trace gas sensors</i> [Dissertation, Technische Universität Wien]. reposiTUm. http://hdl.handle.net/20.500.12708/78567</div>
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dc.identifier.uri
http://hdl.handle.net/20.500.12708/78567
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dc.description
Zusammenfassung in deutscher Sprache
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dc.description.abstract
Within the framework of this doctoral thesis two different spectroscopic schemes of laser based trace gas sensors have been developed. One method utilizes the principle of photoacoustic spectroscopy detecting photo-induced acoustic waves, whereas the other one utilizes the principle of photothermal spectroscopy monitoring photo-induced refractive index changes. The main focus of attention at both techniques was the development of highly sensitive and selective sensors, having ultra-low gas volumes together with a rugged transducer. These are highly appealing features, which are of interest for applications in diverse fields, such as medical diagnostics in terms of breath gas analysis, environmental monitoring or process and exhaust gas analysis. A high sensitivity of the sensors was achieved, on the one hand by using transducers which show a strong response to small changes of the measured physical property, and on the other hand by excitation of strong signals based on the molecular absorption of modulated laser radiation, which causes a periodic heating of the sample. The heating in turn causes the thermodynamic properties of the sample to change resulting in pressure waves and refractive index changes. Strong signal generation was accomplished by the use of quantum cascade lasers. They feature the possibility that they can be designed to emit light at a particular wavelength in the mid-infrared spectral region. At these wavelengths strong fundamental vibrational transitions of molecules in the gas phase can be excited. Furthermore, quantum cascade lasers are based on semiconductor technology, which provides small devices that come along with high optical power. This is essential for the construction of small sensor devices but also for excitation of strong signals, because concerning the studied techniques the excited signal is directly proportional to the incident laser power. A high selectivity of the sensors was achieved by employing wavelength modulation and second harmonic (2f) detection at reduced sample gas pressure, which allows to probe strong, spectroscopic interference-free signals of characteristic molecular absorptions without any background. At first, a compact and portable quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor system for detection of carbon disulfide CS2 at trace concentration levels was developed, which was applicable in harsh environments for process control and workplace safety at viscose fiber industry. It was extensively characterized, optimized as well as calibrated in laboratory yielding a detection limit of about 30 parts per billion by volume (pbbv) for a 1 second time resolution. The performance of this sensor system was investigated by a measurement campaign lasting several days at industry (Lenzing AG, Austria) in comparison with a reference system, by measuring the CS2 concentrations in process streams of regenerated cellulose fiber production. The applicability of the system for industrial applications was successfully proved within this test run, featuring a fast sensor response and the omission of any sample pre-treatment. The second elaborated sensing technique is an innovative concept for sensitive and selective gas detection, featuring a very rugged transducer and an ultra-small absorption volume based on Fabry-Perot photothermal interferometry, within which a photo-induced change in the refractive index is monitored by a measurement of the transmitted intensity of a probe laser through the interferometer. Any refractive index change causes a phase shift of the laser, which can be translated in a change of the transmitted intensity. The use of the Fabry-Perot interferometer type is based upon its advantageous characteristics, such as its very simple design, i.e. two optics, and the easy adjustable sensitivity to refractive index changes, e.g. by means of the mirror reflectivity. The functional principle of the 2f-wavelength modulation Fabry-Perot photothermal interferometer concept employing was proved by the example of SO2 detection using an absorption cell consisting of a low finesse interferometer with a mirror reflectivity of 0.85 and a spacing of 1 mm. Refractive index changes in the sample gas were induced by a quantum cascade excitation laser and monitored by a laser diode emitting at a wavelength in the near-infrared region. This system yielded a detection limit of about 1 parts per million by volume (ppmv) for a time resolution of 1 second. The results of this work illustrate the high potential for a further development of this sensor concept and improvements of the sensor in terms of sensitivity are discussed.
en
dc.format
xiv, 152 Seiten
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dc.language
English
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dc.language.iso
en
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dc.subject
Photoacoustic Spectroscopy
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dc.subject
Photothermal Spectroscopy
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dc.subject
Infrared Spectroscopy
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dc.subject
2f-Wavelength Modulation Spectroscopy
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dc.subject
Quartz Tuning Fork
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dc.subject
Fabry-Perot Interferometer
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dc.subject
Optical Sensing and Sensors
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dc.subject
Semiconductor Laser
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dc.subject
Quantum Cascade Laser
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dc.subject
Trace Gas Monitoring
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dc.title
Development of mid-infrared laser based photoacoustic and photothermal trace gas sensors
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dc.type
Thesis
en
dc.type
Hochschulschrift
de
dc.contributor.affiliation
TU Wien, Österreich
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dc.publisher.place
Wien
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tuw.thesisinformation
Technische Universität Wien
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tuw.publication.orgunit
E164 - Institut für Chemische Technologien und Analytik
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dc.type.qualificationlevel
Doctoral
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dc.identifier.libraryid
AC13427879
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dc.description.numberOfPages
152
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dc.thesistype
Dissertation
de
dc.thesistype
Dissertation
en
tuw.advisor.staffStatus
staff
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tuw.advisor.orcid
0000-0003-3838-5842
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item.fulltext
no Fulltext
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item.cerifentitytype
Publications
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item.openairecristype
http://purl.org/coar/resource_type/c_db06
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item.languageiso639-1
en
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item.openairetype
doctoral thesis
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item.grantfulltext
none
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crisitem.author.dept
E164-02-1 - Forschungsgruppe Prozessanalytik
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crisitem.author.orcid
0000-0003-0291-487X
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crisitem.author.parentorg
E164-02 - Forschungsbereich Umwelt-, Prozessanalytik und Sensoren