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Development of diode laser-based absorption and dispersion spectroscopic techniques for sensitive and selective detection of gaseous species and temperature
Umeå University, Faculty of Science and Technology, Department of Physics. (laser group)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main aim of this thesis has been to contribute to the ongoing work with development of new diode-laser-based spectroscopic techniques and metho­do­lo­gies for sensitive detection of molecules in gas phase. The techniques under scrutiny are tunable diode laser absorption spectrometry (TDLAS) and Faraday modulation spectrometry (FAMOS). Conventional distributed-feedback (DFB) tele­communication diode lasers working in the near-infrared (NIR) region have been used for detection of carbon monoxide (CO) and temperature in hot humid media whereas a unique frequency-quadrupled external-cavity diode laser producing mW powers of continuous-wave (cw) light in the ultra violet (UV) region have been used for detection of nitric oxide (NO).

A methodology for assessment of CO in hot humid media by DFB-TDLAS has been developed. By addressing a particular transition in its 2nd overtone band, and by use of a dual-fitting methodology with a single reference water spectrum for background correction, % concentrations of CO can be detected in media with tens of percent of H2O (≤40%) at T≤1000 °C with an accuracy of a few %. Moreover, using an ordinary DFB laser working in the C-band, a technique for assessment of the temperature in hot humid gases (T≤1000 °C) to within a fraction of a percent has been developed. The technique addresses two groups of lines in H2O that have a favorable temperature dependence and are easily accessed in a single scan, which makes it sturdy and useful for industrial applications.

A technique for detection of NO on its strong electronic transitions by direct absorption spectrometry (DAS) using cw UV diode laser light has been deve­loped. Since the electronic transitions are ca. two or several orders of magnitude stronger than of those at various rotational-vibra­tional bands, the system is capable of detecting NO down to low ppb∙m concentrations solely using DAS.

Also the FAMOS technique has been further developed. A new theoretical description expressed in terms of both the integrated line strength of the transition and 1st Fourier coefficients of a magnetic-field-modulated dispersive lineshape functions is presented. The description has been applied to both ro-vib Q-transitions and electronic transitions in NO. Simulations under different pressures and magnetic field conditions have been made that provide the optimum conditions for both cases. A first demonstration and characteri­zation of FAMOS of NO addressing its electronic transitions in the UV-region has been made, resulting in a detection limit of 10 ppb∙m. The characterization indicates that the technique can be significantly improved if optimum conditions can be obtained, which demonstrates the high potential of the UV-FAMOS technique.

Place, publisher, year, edition, pages
Umeå: Umeå University, Department of Physics , 2011. , 118 p.
Keyword [en]
Absorption Spectrometry (AS), Wavelengh Modulation Absorption Spectrometry (WMAS), Faraday Modulation Spectrometry (FAMOS), Tunable Diode Laser Absorption Spectrometry (TDLAS)
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-43799ISBN: 978-91-7459-190-3OAI: oai:DiVA.org:umu-43799DiVA: diva2:416004
Public defence
2011-06-08, Naturvetarhuset, N420, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-05-13 Created: 2011-05-10 Last updated: 2011-05-10Bibliographically approved
List of papers
1. Methodology for detection of carbon monoxide in hot, humid media by telecommunication distributed feedback laser-based tunable diode laser absorption spectrometry
Open this publication in new window or tab >>Methodology for detection of carbon monoxide in hot, humid media by telecommunication distributed feedback laser-based tunable diode laser absorption spectrometry
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2011 (English)In: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 50, 1-20 p.Article in journal (Refereed) Published
Abstract [en]

Detection of carbon monoxide (CO) in combustion gases by tunable diode laser spectrometry is often hampered by spectral interferences from H2O and CO2. A methodology for assessment of CO in hot humid media using telecommunication DFB lasers is presented. By addressing the R14 line at 6395.4 cm-1, and using a dual-species-fitting technique that incorporates fitting of both a previously measured water background reference spectrum and a 2f-wavelength modulation lineshape function, %-level concentrations of CO can be detected in media with tens percent of water (c(H2O)  ≤ 40 %) at  ≤ 1000 °C with an accuracy of a few percent by the use of a single reference water spectrum for background correction

Identifiers
urn:nbn:se:umu:diva-43801 (URN)
Funder
Swedish Research Council, 621-2008-3674 and 621-2007-5123
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2011-05-10Bibliographically approved
2. Methodology for temperature measurements in water vapor using wavelength-modulation tunable diode laser absorption spectrometry in the telecom C-band
Open this publication in new window or tab >>Methodology for temperature measurements in water vapor using wavelength-modulation tunable diode laser absorption spectrometry in the telecom C-band
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2009 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 97, no 3, 727-748 p.Article in journal (Refereed) Published
Abstract [en]

A methodology based upon wavelength modulation and two-line thermometry for assessment of gas temperature by tunable diode laser absorption spectroscopy utilizing a standard tunable distributed feedback (DFB) diode laser working in the telecom C-band has been developed. Due to the high density of water lines in this wavelength region at elevated temperatures the methodology does not make use of two individual lines, but rather two groups of lines. The two groups identified have been found to have favorable properties for accurate temperature assessment in the 200-1000 ºC range, primarily a separation that is within a single DFB laser scan (~20 GHz), an adequate linestrength, and sufficient difference in temperature dependence; the ratio of the peak-values of the 2f-wm-signals, R, was found to increase monotonically with temperature, T, with a relative sensitivity, (ΔR/R)/(Δ/T), above or around unity for most of the pertinent temperature range. The standard deviation of a temperature measurement with a 1 s integration time was found to be below 0.3 %. The dependence of the temperature assessment on water concentration and modulation amplitude has also been investigated.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-32202 (URN)10.1007/s00340-009-3721-7 (DOI)
Available from: 2010-03-03 Created: 2010-03-03 Last updated: 2012-08-15Bibliographically approved
3. Detection of nitric oxide at low ppb center dot m concentrations by differential absorption spectrometry using a fully diode-laser-based ultraviolet laser system
Open this publication in new window or tab >>Detection of nitric oxide at low ppb center dot m concentrations by differential absorption spectrometry using a fully diode-laser-based ultraviolet laser system
2007 (English)In: Journal of the Optical Society of America B, Vol. 24, no 9, 2294-2306 p.Article in journal (Refereed) Published
Abstract [en]

An instrumentation for detection of nitric oxide (NO) by direct absorption spectrometry in the parts in 109 (ppb) range on its electronic X2 Pi(v(n) = 0)-A(2)Sigma(+)(v' = 0) transition has been constructed around a commercially available fully diode-laser-based laser system producing milliwatts powers of ultraviolet light at similar to 226.6 run, and its analytical performance has been evaluated. It is shown that the system is capable of detecting NO down to 3 ppb . m under low-pressure conditions (at a signal-to-noise ratio of 3 for a signal averaging of 5s), which is 2 orders of magnitude below that of any other diode-laser-based absorption technique. The combined line strength of the targeted lines was assessed to 3.1 X 10(-18) cm(-1)/(molecule cm(-2)), which supersedes typical line strengths of the fundamental vibrational band and the first and second overtone bands of NO by similar to 2, similar to 4, and similar to 5 orders of magnitude, respectively Also the collision broadening and shift of the targeted lines in NO by N-2 have been assessed.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-8605 (URN)
Available from: 2008-01-30 Created: 2008-01-30 Last updated: 2011-05-10Bibliographically approved
4. Quantitative description of Faraday modulation spectrometry in terms of the integrated linestrength and 1st Fourier coefficients of the modulated lineshape function
Open this publication in new window or tab >>Quantitative description of Faraday modulation spectrometry in terms of the integrated linestrength and 1st Fourier coefficients of the modulated lineshape function
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2010 (English)In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 111, no 16, 2415-2433 p.Article in journal (Refereed) Published
Abstract [en]

A quantitative description of the strength and shape of Faraday modulation spectrometry (FAMOS) signals is given. It is first shown how the signal can be expressed in terms of the integrated linestrength for the targeted transition, Si,j. Secondly, since the technique relies on a periodic modulation of the transition frequency induced by an alternating magnetic field, it is explicitly shown that it is possible to express the FAMOS signal concisely in terms of 1st Fourier coefficients of a magnetic-field-modulated dispersive lineshape function for left- and right-handed circularly polarized light. Expressions for the FAMOS signal in terms of the integrated linestrength and such Fourier coefficients are given for three cases: (i) for transitions between two arbitrary types of states, (ii) for transitions between two states that both belong to Hund’s coupling case (a), as is the case for rotational–vibrational transitions of NO, and finally (iii) for the commonly used Q-transitions between such states. It is finally shown that the FAMOS signal from a Q-transition can be expressed succinctly solely in terms of one 1st Fourier coefficient. A general analysis of FAMOS addressing an arbitrary Q-transition as well as the most sensitive Q3/2(3/2) transition in NO is given. The conditions for maximum signal are specifically identified.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
FAMOS, Faraday rotation spectrometry, Magnetic rotation spectrometry, Integrated linestrength, Fourier coefficient; Nitric oxide (NO)
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-36153 (URN)10.1016/j.jqsrt.2010.06.017 (DOI)000282252500006 ()
Available from: 2010-09-20 Created: 2010-09-20 Last updated: 2013-04-23Bibliographically approved
5. Faraday modulation spectrometry of nitric oxide addressing its electronic X2Π − A2Σ+ band: I. theory
Open this publication in new window or tab >>Faraday modulation spectrometry of nitric oxide addressing its electronic X2Π − A2Σ+ band: I. theory
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2010 (English)In: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 49, no 29, 5597-5613 p.Article in journal (Refereed) Published
Abstract [en]

We give a simple two-transition model of Faraday modulation spectrometry (FAMOS) addressing the electronic X2Π(ν''=0) − A2Σ+(ν'=0) band in nitric oxide. The model is given in terms of the integrated line strength, S, and first Fourier coefficients for the magnetic-field-modulated dispersive line shape function. Although the two states addressed respond differently to the magnetic field (they adhere to the dissimilar Hund coupling cases), it is shown that the technique shares some properties with FAMOS when rotational-vibrational Q-transitions are targeted: the line shapes have a similar form and the signal strength has an analogous magnetic field and pressure dependence. The differences are that the maximum signal appears for larger magnetic field amplitudes and pressures, ∼1500 G and ∼200 Torr, respectively.

Place, publisher, year, edition, pages
OSA, The Optical Society, 2010
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-37867 (URN)10.1364/AO.49.005597 (DOI)000282685300012 ()
Available from: 2010-11-17 Created: 2010-11-17 Last updated: 2013-04-23Bibliographically approved
6. Faraday modulation spectrometry of nitric oxide addressing its electronic X2Π - A2Σ+ band: II. experiment
Open this publication in new window or tab >>Faraday modulation spectrometry of nitric oxide addressing its electronic X2Π - A2Σ+ band: II. experiment
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2010 (English)In: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 49, no 29, 5614-5625 p.Article in journal (Refereed) Published
Abstract [en]

A first demonstration of Faraday modulation spectrometry (FAMOS) of nitric oxide (NO) addressing its strong electronic X2Π(ν″=0)−A2Σ+=0) band is presented. The instrumentation was constructed around a fully diode-laser-based laser system producing mW powers of ultraviolet light targeting the overlapping Q22(21/2) and R12Q(21/2) transitions at ∼226.6nm. The work verifies a new two-transition model of FAMOS addressing the electronic transitions in NO given in an accompanying work. Although the experimental instrumentation could address neither the parameter space of the theory nor the optimum conditions, the line shapes and the pressure dependence could be verified under low-field conditions. NO could be detected down to a partial pressure of 13µTorr, roughly corresponding to 10ppb·m for an atmospheric pressure sample, which demonstrates the feasibility of FAMOS for sensitive detection of NO addressing its strong electronic band. A first demonstration of Faraday modulation spectrometry (FAMOS) of nitric oxide (NO) addressing its srtong electronic X2Π - A2Σ+ band is presented. The instrumentation was constructed around a fully diode-laser-based laser system producing mW powers of ultraviolet light targeting the overlapping Q22(21) and QR12(21) transitions at around 226.6 nm. The work verifies a new two-transition model of FAMOS addressing the electronic transitions in NO given in an accompanying work. Although the experimental instrumentation could address neither the parameter space of the theory nor the optimum conditions, the line shapes and the pressure dependence could be verified under low-field conditions. NO could be detected down to a partial pressure of 13 μTorr, roughly corresponding to 10 ppb · mfor an atmospheric pressure sample, which demonstrates the feasibility of FAMOS for sensitive detection of NO addressing its strong electronic band.

Place, publisher, year, edition, pages
OSA, The Optical Society of America, 2010
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-38881 (URN)10.1364/AO.49.005614 (DOI)000282685300013 ()
Available from: 2011-01-10 Created: 2011-01-07 Last updated: 2013-04-23Bibliographically approved

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