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Wang, Junyang
Publications (10 of 14) Show all publications
Ehlers, P., Wang, J., Silander, I. & Axner, O. (2014). Doppler broadened NICE-OHMS beyond the triplet formalism: assessment of optimum modulation index. Journal of the Optical Society of America. B, Optical physics, 31(7), 1499-1507
Open this publication in new window or tab >>Doppler broadened NICE-OHMS beyond the triplet formalism: assessment of optimum modulation index
2014 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 31, no 7, p. 1499-1507Article in journal (Refereed) Published
Abstract [en]

The dependence of Doppler broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) on the modulation index, beta, has been investigated experimentally on C2H2 and CO2, both in the absence and the presence of optical saturation. It is shown that the maximum signals are obtained for beta that produce more than one pair of sidebands: in the Doppler limit and for the prevailing conditions (unsaturated transition and the pertinent modulation frequency and Doppler widths) around 1 and 1.4 for the dispersion and absorption detection phases, respectively. The results verify predictions given in an accompanying work. It is also shown that there is no substantial broadening of the NICE-OHMS signal for beta < 1. The use of beta of unity has yielded a Db-NICE-OHMS detection sensitivity of 4.9 x 10(-12) cm(-1) Hz(-1/2), which is the lowest (best) value so far achieved for NICE-OHMS based on a tunable laser. The number of sidebands that needs to be included in fits of the line-shape function to obtain good accuracy has been assessed. It is concluded that it is enough to consider three pairs of sidebands whenever the systematic errors in a concentration assessment should be below 1% when beta < 2 are used and <1 parts per thousand for beta < 1.5.

Place, publisher, year, edition, pages
Optical Society of America, 2014
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-91852 (URN)10.1364/JOSAB.31.001499 (DOI)000338931700013 ()
Note

Ingår i Patrick Ehlers doktorsavhandling som delarbete nr XI med titeln: NICE-OHMS beyond the triplet formalism: assessment of the optimum modulation index.

Available from: 2014-08-26 Created: 2014-08-18 Last updated: 2018-06-07Bibliographically approved
Ehlers, P., Silander, I., Wang, J., Foltynowicz, A. & Axner, O. (2014). Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry incorporating an optical circulator. Optics Letters, 39(2), 279-282
Open this publication in new window or tab >>Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry incorporating an optical circulator
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2014 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 2, p. 279-282Article in journal (Refereed) Published
Abstract [en]

To reduce the complexity of fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry, a system incorporating a fiber-coupled optical circulator to deflect the cavity-reflected light for laser stabilization has been realized. Detection near the shot-noise limit has been demonstrated for both Doppler-broadened and sub-Doppler signals, yielding a lowest detectable absorption and optical phase shift of 2.2 x 10(-12) cm(-1) and 4.0 x 10(-12) cm(-1), respectively, both for a 10 s integration time, where the former corresponds to a detection limit of C2H2 of 5 ppt. (C) 2014 Optical Society of America

Place, publisher, year, edition, pages
Optical Society of America, 2014
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-85701 (URN)10.1364/OL.39.000279 (DOI)000329906900026 ()
Funder
Swedish Research Council, 621-2011-4216Carl Tryggers foundation
Available from: 2014-02-20 Created: 2014-02-10 Last updated: 2018-06-08Bibliographically approved
Westberg, J., Wang, J. & Axner, O. (2014). Methodology for fast curve fitting to modulated Voigt dispersion lineshape functions. Journal of Quantitative Spectroscopy and Radiative Transfer, 133, 244-250
Open this publication in new window or tab >>Methodology for fast curve fitting to modulated Voigt dispersion lineshape functions
2014 (English)In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 133, p. 244-250Article in journal (Refereed) Published
Abstract [en]

Faraday rotation spectroscopy (FAMOS) as well as other modulated techniques that rely on dispersion produce lock-in signals that are proportional to various Fourier coefficients of modulated dispersion lineshape functions of the molecular transition targeted. In order to enable real-time curve fitting to such signals a fast methodology for calculating the Fourier coefficients of modulated lineshape functions is needed. Although there exist an analytical expression for such Fourier coefficients of modulated Lorentzian absorption and dispersion lineshape functions, there is no corresponding expression for a modulated Voigt dispersion function. The conventional computational route of such Fourier coefficients has therefore so far either consisted of using various approximations to the modulated Voigt lineshape function or solving time-consuming integrals, which has precluded accurate real-time curve fitting. Here we present a new methodology to calculate Fourier coefficients of modulated Voigt dispersion lineshape functions that is significantly faster (several orders of magnitude) and more accurate than previous approximative calculation procedures, which allows for real-time curve fitting to FAMOS signals also in the Voigt regime.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Faraday rotation, Faraday modulation, Spectroscopy, Quantum cascade laser
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-68648 (URN)10.1016/j.jqsrt.2013.08.008 (DOI)000328868800018 ()
Available from: 2013-04-22 Created: 2013-04-22 Last updated: 2018-06-08Bibliographically approved
Axner, O., Ehlers, P., Foltynowicz, A., Silander, I. & Wang, J. (2014). NICE-OHMS – frequency modulation cavity-enhanced spectroscopy: principles and performance. In: Gianluca Gagliardi and Hans-Peter Loock (Ed.), Cavity-Enhanced Spectroscopy and Sensing: (pp. 221-251). Berlin: Springer Berlin/Heidelberg
Open this publication in new window or tab >>NICE-OHMS – frequency modulation cavity-enhanced spectroscopy: principles and performance
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2014 (English)In: Cavity-Enhanced Spectroscopy and Sensing / [ed] Gianluca Gagliardi and Hans-Peter Loock, Berlin: Springer Berlin/Heidelberg, 2014, p. 221-251Chapter in book (Refereed)
Abstract [en]

Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is a sensitive technique for detection of molecular species in gas phase. It is based on a combination of frequency modulation for reduction of noise and cavity enhancement for prolongation of the interaction length between the light and a sample. It is capable of both Doppler-broadened and sub-Doppler detection with absorption sensitivity down to the 10−12 and 10−14 Hz−1/2 cm−1 range, respectively. This chapter provides a thorough description of the basic principles and the performance of the technique.

Place, publisher, year, edition, pages
Berlin: Springer Berlin/Heidelberg, 2014
Series
Springer Series in Optical Sciences, ISSN 0342-4111 ; 179
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-84914 (URN)10.1007/978-3-642-40003-2_6 (DOI)978-3-642-40002-5 (ISBN)978-3-642-40003-2 (ISBN)
Available from: 2014-01-22 Created: 2014-01-22 Last updated: 2018-06-08Bibliographically approved
Wang, J., Ehlers, P., Silander, I. & Axner, O. (2014). On the accuracy of the assessment of molecular concentration and spectroscopic parameters by frequency modulation spectrometry and NICE-OHMS. Journal of Quantitative Spectroscopy and Radiative Transfer, 136, 28-44
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, p. 28-44Article 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.

Keywords
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: 2018-06-07Bibliographically approved
Wang, J. (2013). 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. (Doctoral dissertation). Umeå: Umeå Universitet
Open this publication in new window or tab >>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
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Dicke-avsmalning och hastighetsberoende effekter hos dispersionssignaler : Påverkan på bestämning av koncentration och spektrala parametrar genom brusimmun kavitetsförstärkt optisk heterodyn molekylär spektrometri
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. p. 89
Keywords
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:nbn:se:umu:diva-70235 (URN)978-91-7459-628-1 (ISBN)978-91-7459-627-4 (ISBN)
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: 2018-06-08Bibliographically approved
Westberg, J., Wang, J. & Axner, O. (2012). Fast and non-approximate methodology for calculation of wavelength-modulated Voigt lineshape functions suitable for real-time curve fitting. Journal of Quantitative Spectroscopy and Radiative Transfer, 113(16), 2049-2057
Open this publication in new window or tab >>Fast and non-approximate methodology for calculation of wavelength-modulated Voigt lineshape functions suitable for real-time curve fitting
2012 (English)In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 113, no 16, p. 2049-2057Article in journal (Refereed) Published
Abstract [en]

Wavelength modulation (WM) produces lock-in signals that are proportional to various Fourier coefficients of the modulated lineshape function of the molecular transition targeted. Unlike the case for the Lorentzian lineshape function, there is no known analytical expression for the Fourier coefficients of a modulated Voigt lineshape function; they consist of nested integrals that have to be solved numerically, which is often time-consuming and prevents real-time curve fitting. Previous attempts to overcome these limitations have so far consisted of approximations of the Voigt lineshape function, which brings in inaccuracies. In this paper we demonstrate a new means to calculate the lineshape of nf-WM absorption signals from a transition with a Voigt profile. It is shown that the signal can conveniently be expressed as a convolution of one or several Fourier coefficients of a modulated Lorentzian lineshape function, for which there are analytical expressions, and the Maxwell-Boltzmann velocity distribution for the system under study. Mathematically, the procedure involves no approximations, wherefore its accuracy is limited only by the numerical precision of the software used (in this case similar to 10(-16)) while the calculation time is reduced by roughly three orders of magnitude (10(-3)) as compared to the conventional methodology, i.e. typically from the second to the millisecond range. This makes feasible real-time curve fitting to lock-in output signals from modulated Voigt profiles. (C) 2012 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Oxford: Elsevier, 2012
Keywords
Voigt lineshape, Wavelength modulation, 2f-signal, Convolution, TDLAS
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-61349 (URN)10.1016/j.jqsrt.2012.05.023 (DOI)000309574400009 ()
Available from: 2012-11-20 Created: 2012-11-12 Last updated: 2018-06-08Bibliographically approved
Ehlers, P., Silander, I., Wang, J. & Axner, O. (2012). 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. Journal of the Optical Society of America. B, Optical physics, 29(6), 1305-1315
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, p. 1305-1315Article 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: 2018-06-08Bibliographically approved
Silander, I., Ehlers, P., Wang, J. & Axner, O. (2012). Frequency modulation background signals from fiber-based electro optic modulators are caused by crosstalk. Journal of the Optical Society of America. B, Optical physics, 29(5), 916-923
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, p. 916-923Article 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: 2018-06-08Bibliographically approved
Wang, J., Ehlers, P., Silander, I. & Axner, O. (2012). 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. Journal of the Optical Society of America. B, Optical physics, 29(10), 2980-2989
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, p. 2980-2989Article 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: 2018-06-08Bibliographically approved
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