umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Dicke narrowing and speed-dependent effects in dispersion signals: Influence on assessment of concentration and spectral parameters by noise-immune cavity-enhanced optical heterodyne molecular spectrometry
Umeå University, Faculty of Science and Technology, Department of Physics.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Dicke-avsmalning och hastighetsberoende effekter hos dispersionssignaler : Påverkan på bestämning av koncentration och spektrala parametrar genom brusimmun kavitetsförstärkt optisk heterodyn molekylär spektrometri (Swedish)
Abstract [en]

Laser spectroscopic techniques have, during the last decades, demonstrated an extraordinary capability for sensitive detection of molecular constituents in gas phase. Since spectra from such techniques constitute unique and characteristic signatures for each type of species, these techniques enable investigations of molecular structures as well as detection of the presence of species in a gas mixture. They are therefore used for a variety of application, from fundamental studies to the assessment of gas concentrations. In fact, quantitative assessments of gas concentrations by laser-based techniques are constantly gaining in popularity, primarily due to properties such as high sensitivity and selectivity and an ability to perform non-invasive measurement. Moreover, investigations of isolated molecular transitions under different conditions provide excellent means to obtain a comprehensive understanding of spectral broadening mechanisms, which is of importance for, for example, environmental sciences and remote sensing applications. In fundamental studies, spectroscopic parameters are often retrieved from fits of a model function of the technique used, which in turn is based upon a suitable lineshape function. In order to obtain parameter values with highest possible accuracy, it is of importance to use the lineshape model that most correctly can predict the measured spectra. Even though the Voigt function is the most commonly used lineshape model when both Doppler and collision broadenings are present, it is not always suitable when spectroscopic parameters are to be assessed with high precision.

This thesis represents a thorough investigation of Dicke narrowing and speed-dependent effects, which are phenomena that are not accounted for by the conventional Voigt profile. For the first time, it is demonstrated that both these effects take place not only in absorption but also in the dispersion mode of detection. Their dispersion lineshape functions are first theoretically presumed and explicitly given before they are validated experimentally by the noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS). By using the models developed, it is also shown that although the two modes of detection, absorption and dispersion, both can provide good quality of fits, they do not always provide identical spectroscopic parameters. A detailed analysis under which conditions they do so, and subsequent recommendations of their use, are presented.

It also describes the instrumental implementation of a distributed-feed-back (DFB) laser-based NICE-OHMS instrumentation, which constitutes an important step towards the further development of this technique. Due to the wide tunability of the DFB laser, the setup is capable of extending the working range of NICE-OHMS into the collision broadening region, which, in turn, allows for precise spectroscopic studies. The use of a fiber-coupled DFB laser also provides a compact NICE-OHMS system. The minimum detectable on-resonance absorption was assessed to 2× 10-10 cm-1 for a 70 s integration time.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2013. , 89 p.
Keyword [en]
Dicke narrowing, Speed-dependent effects, Dispersion signals, Noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS), accuracy
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:umu:diva-70235ISBN: 978-91-7459-628-1 (print)ISBN: 978-91-7459-627-4 (print)OAI: oai:DiVA.org:umu-70235DiVA: diva2:620527
Public defence
2013-06-04, Naturvetarhuset, N420, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2013-05-14 Created: 2013-05-08 Last updated: 2014-06-16Bibliographically approved
List of papers
1. Distributed-feedback-laser-based NICE-OHMS
in the pressure-broadened regime
Open this publication in new window or tab >>Distributed-feedback-laser-based NICE-OHMS
in the pressure-broadened regime
2010 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 18, 18580-18591 p.Article in journal (Refereed) Published
Abstract [en]

A compact noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) system based on a narrow linewidth distributed-feedback laser and fiber-coupled acousto-optic and electro-optic modulators has been developed. Measurements of absorption and dispersion signals have been performed at pressures up to 1/3 atmosphere on weak acetylene transitions at 1551 nm. Multiline fitting routines were implemented to obtain transition parameters, i.e., center frequencies, linestrengths, and pressure broadening coefficients. The signal strength was shown to be linear with pressure and concentration, and independent of detection phase. The minimum detectable on-resonance absorption with a cavity with a finesse of 460 was 2 × 10−10 cm−1 for 1 minute of integration time.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-36156 (URN)10.1364/OE.18.018580 (DOI)000282107900009 ()
Available from: 2010-09-21 Created: 2010-09-21 Last updated: 2017-12-12Bibliographically approved
2. Dicke narrowing in the dispersion mode of detection and in noise-immune cavity-enhanced optical heterodyne molecular spectroscopy-theory and experimental verification
Open this publication in new window or tab >>Dicke narrowing in the dispersion mode of detection and in noise-immune cavity-enhanced optical heterodyne molecular spectroscopy-theory and experimental verification
2011 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 28, no 10, 2390-2401 p.Article in journal (Refereed) Published
Abstract [en]

Dicke narrowing in both the absorption and dispersion modes of detection have been scrutinized by noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using an isolated transition in the v(1) + v(3) + v(4)(1) - v(4)(1) band of acetylene [P(e)(33) at 6439.371 cm(-1)] at room temperature. The results represent the first (to our knowledge) demonstration of Dicke narrowing detected in dispersion, as well as by NICE-OHMS, and the paper provides thereby the first comparison of the Dicke narrowing phenomenon for the two modes of detection. It is shown that Dicke narrowing in dispersion can be described by the dispersive counterparts to the conventional Galatry and Rautian absorption line-shape functions, which are explicitly given. Spectroscopic parameters for the targeted transition were extracted in both absorption and dispersion and found to be in agreement with those previously reported for other lines and bands. The shortcomings of the Galatry model to provide physically relevant parameters in this pressure range are discussed.

Place, publisher, year, edition, pages
Washington, D. C.: The Optical Society of America, 2011
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-49570 (URN)10.1364/JOSAB.28.002390 (DOI)000296045400014 ()
Available from: 2011-11-22 Created: 2011-11-14 Last updated: 2017-12-08Bibliographically approved
3. Speed-dependent Voigt dispersion line-shape function: applicable to techniques measuring dispersion signals
Open this publication in new window or tab >>Speed-dependent Voigt dispersion line-shape function: applicable to techniques measuring dispersion signals
Show others...
2012 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 10, 2971-2979 p.Article in journal (Refereed) Published
Abstract [en]

An analytical expression for a Voigt dispersion line-shape function that incorporates speed-dependent effects (SDEs) on the collision broadening, applicable to spectroscopic techniques that measure dispersion signals, is presented. It is based upon a speed-dependent Voigt (SDV) model for absorption spectrometry that assumes that the molecular relaxation rate has a quadratic dependence on molecular speed. The expression is validated theoretically in the limit of small SDEs by demonstration that it reverts to the ordinary Voigt dispersion line-shape function and experimentally in a separate work by experiments performed by the noise-immune cavity-enhanced optical heterodyne molecular spectrometry technique. A comparison is given between the SDEs in the SDV absorption and dispersion line-shape functions. It is shown that both line shapes are affected significantly but differently by SDEs. The expression derived provides, for the first time to our knowledge, a possibility also for the techniques that measure dispersion signals to handle SDEs. (c) 2012 Optical Society of America

Place, publisher, year, edition, pages
Washington: Optical Society of America, 2012
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-61566 (URN)10.1364/JOSAB.29.002971 (DOI)000309588200045 ()
Available from: 2012-11-28 Created: 2012-11-20 Last updated: 2017-12-07Bibliographically approved
4. Speed-dependent effects in dispersion mode of detection and in noise-immune cavity-enhanced optical heterodyne molecular spectrometry: experimental demonstration and validation of predicted line shape
Open this publication in new window or tab >>Speed-dependent effects in dispersion mode of detection and in noise-immune cavity-enhanced optical heterodyne molecular spectrometry: experimental demonstration and validation of predicted line shape
2012 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 10, 2980-2989 p.Article in journal (Refereed) Published
Abstract [en]

Speed-dependent effects (SDEs) in both the absorption and dispersion modes of detection have been detected and scrutinized by the noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) technique. The present paper achieves four objectives: (i) it provides the first demonstration of SDEs detected in dispersion, (ii) it validates the expression for a speed-dependent Voigt (SDV) dispersion line-shape function that is derived in an accompanying paper, (iii) it illustrates the influence of SDEs on the NICE-OHMS technique, and (iv) it gives the first experimental comparison of SDEs for the absorption and dispersion modes of detection. Experiments were performed using an isolated transition in the v(1) + v(3) + v(4)(1) - v(4)(1) band of acetylene [P-e (33) at 6439.371 cm(-1)] in the 100-250 Torr range at room temperature. It is shown that SDEs appear in both the absorption and dispersion modes of detection, that they can be well described by the suggested SDV dispersion line-shape function, and that they need to be taken into account if NICE-OHMS signals detected under optimal pressures are to be properly assessed. (c) 2012 Optical Society of America

Place, publisher, year, edition, pages
Washington: Optical Society of America, 2012
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-61567 (URN)10.1364/JOSAB.29.002980 (DOI)000309588200046 ()
Available from: 2012-11-28 Created: 2012-11-20 Last updated: 2017-12-07Bibliographically approved
5. Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry instrumentation for Doppler-broadened detection in the 10-12 cm-1 Hz-1/2 region
Open this publication in new window or tab >>Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry instrumentation for Doppler-broadened detection in the 10-12 cm-1 Hz-1/2 region
2012 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 6, 1305-1315 p.Article in journal (Refereed) Published
Abstract [en]

A fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry (FL-NICE-OHMS) system for white-noise-limited Doppler-broadened detection down to 5.6 x 10(-12) cm(-1) Hz(-1/2) is demonstrated. The system is based on a previous FL-NICE-OHMS instrumentation in which the locking of the laser frequency to a cavity mode has been improved by the use of an acousto-optic modulator (AOM) and provision of a more stable environment by the employment of a noise-isolating enclosed double-layer table, a temperature regulation of the laboratory, and an ultra-high-vacuum (UHV) gas system. White-noise behavior up to 10 s provides the instrument with a minimum detectable on-resonance absorbance per unit length of 1.8 x 10(-12) cm(-1) and a relative single-pass absorption (Delta I/I) of 7.2 x 10(-11). The system was applied to detection of acetylene on a transition at 1531.588 nm, yielding a detection sensitivity of C2H2 in atmospheric pressure gas of 4 ppt (measured over 10 s). (C) 2012 Optical Society of America

Place, publisher, year, edition, pages
Optical Society of America, 2012
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-56987 (URN)10.1364/JOSAB.29.001305 (DOI)000305029900023 ()
Available from: 2012-07-03 Created: 2012-07-02 Last updated: 2017-12-07Bibliographically approved
6. Frequency modulation background signals from fiber-based electro optic modulators are caused by crosstalk
Open this publication in new window or tab >>Frequency modulation background signals from fiber-based electro optic modulators are caused by crosstalk
2012 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 5, 916-923 p.Article in journal (Refereed) Published
Abstract [en]

Frequency modulated spectroscopy (FMS) performed by the use of fiber-coupled electro optic modulators (FC-EOMs) is often plagued by background signals that bring in noise and, by their temperature dependence, cause severe drifts. These signals cannot be zeroed out by the conventional technique of using a carefully adjusted polarizer that can be applied to free space electro optic modulators (EOMs). This can limit the use of FC-EOMs in high performance detection techniques. Here we provide an explanation to these background signals that is based upon crosstalk between various polarization directions of light in the fixed mounted polarization-maintaining fibers and the electro optic crystal. The description provides a basis for the previously demonstrated technique that utilizes an EOM regulated simultaneously by temperature and DC voltage to eliminate background signals from systems encompassing FC-EOMs. (C) 2012 Optical Society of America

Place, publisher, year, edition, pages
Optical Society of America, 2012
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-55672 (URN)10.1364/JOSAB.29.000916 (DOI)000303544000007 ()
Available from: 2012-05-30 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
7. NICE-OHMS – Frequency modulation cavity-enhanced spectroscopy: principles and performance
Open this publication in new window or tab >>NICE-OHMS – Frequency modulation cavity-enhanced spectroscopy: principles and performance
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-70231 (URN)
Available from: 2013-05-08 Created: 2013-05-08 Last updated: 2015-10-22
8. On the accuracy of the assessment of molecular concentration and spectroscopic parameters by frequency modulation spectrometry and NICE-OHMS
Open this publication in new window or tab >>On the accuracy of the assessment of molecular concentration and spectroscopic parameters by frequency modulation spectrometry and NICE-OHMS
2014 (English)In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 136, 28-44 p.Article in journal (Refereed) Published
Abstract [en]

Frequency modulation spectrometry (FMS), and thereby also noise immune cavity enhanced optical heterodyne molecular spectrometry (NICE-OHMS), can detect both absorption and dispersion signals, and can therefore, by curve fitting, extract molecular parameters from both these types of signals. However, parameters evaluated from the two modes of detection have been previously shown not to be identical. Their accuracy is affected by both the type of lineshape used by the fit and the accuracy of the detection phase. A thorough study is presented of the influence of three lineshape functions [Voigt, Rautian, and speed-dependent Voigt (SDV)] and errors in the detection phase on the retrieval of various molecular parameters, in particular the signal strength, which provides information about the concentration of molecules in a gas, from reference spectra in the 10-260 Torr region. It was found that for data detected and evaluated at pure absorption or dispersion phase by a system calibrated in the Doppler limit the signal strength can be underestimated at higher pressures by up to 45% if the evaluation is made using the Voigt profile. If the detection is plagued by phase errors additional inaccuracies, often in the order of percent per degree phase error (%/deg), can occur. More reliable parameters can be obtained if an appropriate lineshape function is used and the detection phase is considered a free parameter. However, despite this, none of the evaluation procedures can retrieve the molecular parameters fully correctly; the most accurate assessments of the signal strength, obtained when the data is detected close to absorption phase and evaluated by the SDV lineshape function, are still associated with an error of a few percent. (C) 2013 Elsevier Ltd. All rights reserved.

Keyword
Frequency modulation spectrometry, Lineshapes, Absorption, Dispersion, Detection phase, Parameter assessments
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-88332 (URN)10.1016/j.jqsrt.2013.12.017 (DOI)000332814300003 ()
Note

Included in thesis in manuscript form with the title "On the accuracy of the assessment of concentration and spectroscopic parameters by frequency modulation spectrometry and NICE-OHMS"

Available from: 2014-06-16 Created: 2014-04-30 Last updated: 2017-12-05Bibliographically approved

Open Access in DiVA

Dicke narrowing and speed-dependent effects in dispersion signals(4149 kB)863 downloads
File information
File name FULLTEXT01.pdfFile size 4149 kBChecksum SHA-512
902a4c098f334a3e81632671777593c28e0e897e3e78bdfd092d58593183ef3864ce6ef385ed2c66d2c9930b54fb0d6145b1056799f0a25de45a2ae70a4e259c
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Wang, Junyang
By organisation
Department of Physics
Atom and Molecular Physics and Optics

Search outside of DiVA

GoogleGoogle Scholar
Total: 863 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 569 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf