umu.sePublications
Change search
Refine search result
4567 301 - 345 of 345
CiteExportLink to result list
Permanent 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
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 301.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    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 spectrometry2013Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 302.
    Wang, Junyang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dicke narrowing in the dispersion mode of detection and in noise-immune cavity-enhanced optical heterodyne molecular spectroscopy-theory and experimental verification2011In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 28, no 10, p. 2390-2401Article in journal (Refereed)
    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.

  • 303.
    Wang, Junyang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    On the accuracy of the assessment of molecular concentration and spectroscopic parameters by frequency modulation spectrometry and NICE-OHMS2014In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 136, p. 28-44Article in journal (Refereed)
    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.

  • 304.
    Wang, Junyang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    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 shape2012In: 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)
    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

  • 305.
    Wang, Junyang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Westberg, Jonas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Speed-dependent Voigt dispersion line-shape function: applicable to techniques measuring dispersion signals2012In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 10, p. 2971-2979Article in journal (Refereed)
    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

  • 306.
    Wang, Menglin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of transitions in Iinduced by a green and a red fix-frequency He-Ne laser2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis is to use laser-induced fluorescence (LIF) spectroscopy to find the possible transitions of Iodine molecule which can be induced by a green or a red Helium-Neon (He-Ne) laser. By simulating all of the possible absorption transitions that a laser can induce, the possible lower and higher energy levels can be found. Then, by simulating and comparing the fluorescence emissions from each of the higher states to the measured fluorescence spectra obtained from the experiment, the correct laser induced transition(s) can be found. We found that the green He-Ne laser can induce a transition from v''=0,  J''=108 to v'=27,  J'=109, and the red He-Ne laser can induce two transitions from v''=3,  J''=34 to v´=6,  J'=33, and v''=5,  J''=129 to v'=11, J'=130. The main error source is considered to be the inaccuracies in the constants and also approximations that we use to simulate the possible transitions, in addition to the extrapolation in the calibration of the spectrometer.

  • 307.
    Wang, Na
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hollow cathode lamps – Means of operation and characterization and origin of their emission2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this experiment is to get the basic understanding of the operating principles of hollow cathode lamp, and to characterize the emission of the Rb-element and Ti-element lamp. The spectrum of the lamps is detected by a grating spectrometer and CCD detector. The origin of their emission and different parts of the spectrum including which type of atoms they emitted from, which specific transition they matched and the upper level, lower level and relative intensity correspondingly are identified by comparing with the NIST database. After all the current dependence on the lines emitted from different types of atoms is analyzed quantitatively.

    The emission from the gas medium of the lamp Ne can be classified into 3 groups: 4p-4s, 3s-3p, 3p-3d for both lamps because they contain the same gas medium, and the maximum absorption lines of the cathode element of each lamp are also be identified. The intensity of 2 Rb lines varies with current i2.94, i3.27 while that of Ti element have the current dependence i3.62i3.68 respectively. Adding a lens in front of the lamp made a great improvement for the shape of spectrum.

  • 308.
    Weng, Nuoshi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of Transitions in Iodine Induced by a Green and a Yellow HeNe Laser2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of the experiment is to find out which transitions induces Iodine by a green and a yellow He-Ne laser measuring the fluorescence spectra. The iodine molecule would be excited by a laser beam in a transition from ground state  X1Σg+ to excited state B3Π0+u. Matlab was used to calculate the possible transitions induced by the laser to find out the possible energy level and to simulate possible fluorescence spectra which were compared with the fluorescence spectrum obtained from the laboratory detection. According to the results, for the green laser, a possible laser addressed transition was identified to be from v''=0, j''=103 to v'=27, j'=104 . For the yellow laser the transition from v''=2, j''=186 to v'=17, j'=187 was identified.

  • 309. Wenz, J.
    et al.
    Döpp, A.
    Khrennikov, K.
    Schindler, S.
    Gilljohann, M. F.
    Ding, H.
    Götzfried, J.
    Buck, A.
    Xu, J.
    Heigoldt, M.
    Helml, W.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Karsch, S.
    Dual-energy electron beams from a compact laser-driven accelerator2019In: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893, Vol. 13, p. 263-269Article in journal (Refereed)
    Abstract [en]

    Ultrafast pump–probe experiments open the possibility to track fundamental material behaviour, such as changes in electronic configuration, in real time. To date, most of these experiments are performed using an electron or a high-energy photon beam that is synchronized to an infrared laser pulse. Entirely new opportunities can be explored if not only a single, but multiple synchronized, ultrashort, high-energy beams are used. However, this requires advanced radiation sources that are capable of producing dual-energy electron beams, for example. Here, we demonstrate simultaneous generation of twin-electron beams from a single compact laser wakefield accelerator. The energy of each beam can be individually adjusted over a wide range and our analysis shows that the bunch lengths and their delay inherently amount to femtoseconds. Our proof-of-concept results demonstrate an elegant way to perform multi-beam experiments in the future on a laboratory scale.

  • 310.
    Westberg, Jonas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Faraday modulation spectroscopy: Theoretical description and experimental realization for detection of nitric oxide2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Faraday modulation spectroscopy (FAMOS) is a laser-based spectroscopic dispersion technique for detection of paramagnetic molecules in gas phase. This thesis presents both a new theoretical description of FAMOS and experimental results from the ultra-violet (UV) as well as the mid-infrared (MIR) regions. The theoretical description, which is given in terms of the integrated linestrength and Fourier coefficients of modulated dispersion and absorption lineshape functions, facilitates the description and the use of the technique considerably. It serves as an extension to the existing FAMOS model that thereby incorporates also the effects of lineshape asymmetries primarily originating from polarization imperfections. It is shown how the Fourier coefficients of modulated Lorentzian lineshape functions, applicable to the case with fully collisionally broadened transitions, can be expressed in terms of analytical functions. For the cases where also Doppler broadening needs to be included, resulting in lineshapes of Voigt type, the lineshape functions can be swiftly evaluated (orders of magnitude faster than previous procedures) by a newly developed method for rapid calculation of modulated Voigt lineshapes (the WWA-method). All this makes real-time curve fitting to FAMOS spectra feasible. Two experimental configurations for sensitive detection of nitric oxide (NO) by the FAMOS technique are considered and their optimum conditions are determined. The two configurations target transitions originating from the overlapping Q22(21=2) and QR12(21=2) transitions in the ultra-violet (UV) region (227nm) and the Q3=2(3=2)-transition in the fundamental rotational-vibrational band in the mid-infrared (MIR) region (5.33 µm). It is shown that the implementations of FAMOS in the UV- and MIR-region can provide detection limits in the low ppb range, which opens up the possibility for applications where high detection sensitivities of NO is required.

  • 311.
    Westberg, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lineshape asymmetries in Faraday modulation spectroscopy2014In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 116, no 2, p. 467-476Article in journal (Refereed)
    Abstract [en]

    Faraday modulation/rotation spectroscopy (FAMOS/FRS) is a spectroscopic technique for detection of paramagnetic species in gas phase. Although the prevailing theoretical description predicts fully symmetrical lineshapes, experiments do not in general provide such. This work shows that asymmetries in FAMOS can have at least two origins; (i) a frequency dependent laser intensity and (ii) polarization imperfections, which both are scrutinized here. A general analytical description for the latter, derived under the assumption that both the polarization imperfections and the relative absorption are small, is presented, conveniently expressed in terms of 1st Fourier coefficients of modulated dispersion and absorption lineshape functions. The resulting expression, which is thus an extension to the conventional FAMOS expression, can thereby be swiftly evaluated and allows for on-line fitting to measured asymmetric FAMOS signals. Curve fits to experimentally obtained data from nitric oxide measured both in the ultra-violet and the mid-infrared region demonstrate the applicability of the methodology.

  • 312.
    Westberg, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kluczynski, Pawel
    Lundqvist, Stefan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Analytical expression for the nth Fourier coefficient of a modulated Lorentzian dispersion lineshape function2011In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 112, no 9, p. 1443-1449Article in journal (Refereed)
    Abstract [en]

    Modulated spectroscopic detection techniques that rely on dispersion, e.g. Faraday modulation/rotation spectroscopy and wavelength-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy, are often described in terms of Fourier coefficients of a modulated dispersion lineshape function. This work derives a non-complex analytical expression for the nth Fourier coefficient of a modulated Lorentzian dispersion lineshape function. The expression is easier to implement, and orders of magnitude faster to execute, than previous approaches involving numerical calculations of integrals. The first six Fourier coefficients are explicitly given and illustrated for their optimum modulation amplitudes, which are also given

  • 313.
    Westberg, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lathdavong, Lemthong
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dion, Claude M.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shao, Jie
    Institute of Information Optics of Zhejiang Normal University, Jinhua, China.
    Kluczynski, Pawel
    Siemens AB, Göteborg, Sweden.
    Lundqvist, Stefan
    Siemens AB, Göteborg, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Quantitative description of Faraday modulation spectrometry in terms of the integrated linestrength and 1st Fourier coefficients of the modulated lineshape function2010In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 111, no 16, p. 2415-2433Article in journal (Refereed)
    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.

  • 314.
    Westberg, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Methodology for fast curve fitting to modulated Voigt dispersion lineshape functions2014In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 133, p. 244-250Article in journal (Refereed)
    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.

  • 315. Wette, Patrick
    et al.
    Engelbrecht, Andreas
    Salh, Roushdey
    Institut f¨ur Physik, Johannes Gutenberg-Universität, Staudinger Weg 7, D-55128 Mainz, Germany.
    Klassen, Ina
    Menke, Dirk
    Herlach, Dieter M.
    Roth, Stephan V.
    Schöpe, Hans Joachim
    Competition between heterogeneous and homogeneous nucleation near a flat wall2009In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 21, no 46, p. 464115-Article in journal (Refereed)
  • 316.
    Wu, Hao
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Design and calibration of optical tweezers using the power spectrum method2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this experiment was to calibrate the optical tweezers by using the power spectrum method. We constructed an optical tweezers which was steerable in the x and y directions. The experimental setup contained three parts mainly: particle trapping, illumination and data processing. The system could manipulate and observe the particle. Our results showed that the trap stiffnesses are both 0.507pN/μm in x and y axis for 1 μm bead.

  • 317.
    Wu, Xiaomei
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Measurement of the temperature dependent emission spectrum from a super luminescent diode with a Fourier transform spectrometer2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A Fourier spectrometer based on the Michelson interferometer is realized to measure and analysis the emission spectrum of a red light emitting diode(LED). Using liquid nitrogen to cool the LED, the temperature dependence of the diodes spectrum was investigated. For room temperature the HWHM (half width half maximum) of the LED was found to be 7.80 nm with a center wavelength at 628.0 nm. For lower temperatures the diode was blue shifted. This phenomenon was attributed to the increase of the width of the forbidden band.

  • 318.
    Xiao, Weiyao
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of the temperature dependence of the emission spectrum from a super luminescent diode by the use of a Fourier transform spectrometer2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this experiment, we use a Fourier transform spectrometer to measure the spectrum of a superluminescent diode. The spectrometer is built using a Michelson interferometer with a motorized mirror in one arm of the interferometer. Another Michelson interferometer that shares the movable mirror is used to calibrate the frequency scale of the spectrometer. We use a green laser to calibrate the spectrometer and get the resolution of system of 0.4 nm. At room temperature, we measure the half width at half maximum of the diode spectrum of 14.4(4) nm and the central wavelength is 624.3(4) nm. We find that the spectrum will red shift when the temperature increases from liquid nitrogen temperature. We conclude that this red shift is due to the decrease of the band gap.

  • 319.
    Xiao, Xiaotong
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction and use of a Watt balance for high precision measurements of the evaporation rate of liquids2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this project, we measure the evaporation rate of methanol using a Watt balance with the precision of mass measurement down to 0.1 mg. We use the velocity mode of the Watt balance to obtain the product BL that is used later to obtain the precise mass of methanol in the force mode. Using the force mode, we determine the change of the mass of methanol droplet as it evaporates, and thus obtain the evaporation rate at room temperature. We find that the evaporation rate is not constant in time and that it depends on the mass and thus surface area of the methanol droplet. The average rate of evaporation, i.e. dm/dt is approx. -1.847(7)x10-3 x m 1/s in the range of masses from 56 mg to 12 mg. The mass of methanol as the function of time is found to follow relation

    m = 5.6(2)x10-5x e-1-847(7) x 10-3 x tm kg

    where tm is time.

  • 320.
    Yang, Liu
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of excitation transitions in iodine induced by a red and a yellow HeNe laser2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this experiment, fluorescence spectra of iodine induced by two fix-frequency He-Ne lasers with different wavelengths were obtained by constructing a laser induced fluorescence system. The possible theoretical transitions between the electronic ground state X1 Σg+ and the excited electronic state B3 Π0+u that are similar to the laser energy were found by simulation assuming a Morse potential for the vibrational of the molecule. By also comparing the simulated fluorescence spectrum and the measured fluorescence spectrum, the transitions which are most probably addressed by the laser can be identified. For the red He-Ne laser the transition R(78)12←6 was identified to lead to a fluorescence spectrum in good agreement with the measured spectrum. And for the yellow laser the transition R(185)17←2 was found as the most probable laser addressed transition. For the yellow laser, the fluorescence spectrum at lower wave numbers shows two additional peaks closing to the peaks identified to come from the main laser addressed level. The additional peaks might come either from an additional laser addressed level or from molecules in the excited state redistributed to another state with similar energy by collisions.

  • 321.
    Yang, Wenqing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of transitions in I2 induced by an orange and a yellow fix-frequency HeNe laser2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis is to study the energy structure of the molecular Iodine and to assess the exact rovibronic transitions induced by two fix-frequency Helium-Neon (He-Ne) lasers (an ''orange" and a ''yellow"). We construct a laser-induced fluorescence (LIF) spectroscopy system detecting the fluorescence spectra produced by excitation of the molecular Iodine vapor with He-Ne lasers. By stimulating all possible excitation routes and corresponding fluorescence spectrum, we compare the experimental spectrum to the calculated spectrum, and determine the exact rovibronic transitions each laser induces. We find that He-Ne lasers induce rovibronic transitions between the ground state X 1Σ+g and the excited state B 3Π+0u of the molecular Iodine: the orange He-Ne laser from v''=2, J''=49 to v'=9, J'=50; and the yellow He-Ne laser includes emission both from v''=3, J''=182 to v'=19, J'=183, and from v''=2, J''=188 to v'=17, J'=189.

  • 322.
    Yao, Jianan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessing the diffusing constant of a microparticle using digital holagraphic imaging with plane wavefronts2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this work, we designed a simple digital holographic imaging system to access the diffusion constants of micro-particles, we used the holograms to get three-dimension position information based on Fresnel-Kirchhoff diffraction formula. Meanwhile, we used the angular spectrum method for numerical reconstruction. Based on the reconstruction images, we measured diffusion constants in x, y, and z direction and got 4.420*10-13 m2/s, 4.830*10-13 m2/s, 3.801*10-13 m2/s with error 2.77%, 6.24% and 16.4% respectively. The error in z axis can be caused by the misalignment among sample stage, laser beam and camera detector, which induced that the shape of hologram and the conversion factor on the pixel size were shifted. Moreover, the algorithm for background subtraction and camera resolution could be improved to get higher hologram quality, which would highly increase the accuracy of measurement.

  • 323.
    Zachmann, Nils
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterisation of a Gas Modulation Refractometer for Detection of Gases at 1550 nm2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Only very few molar polarizabilities are known with high accuracy; and when so, they are in general only known at a given wavelength. There is therefore a need to assess the molar polarizability with high accuracy of various gases, at different wavelengths.

    The molar polarizability of a gas is a measure of the susceptibility of a molecule to have its charge distribution affected by light. It is also the entity that relates the index of refraction to the (molar) density of a gas in Lorentz-Lorenz equation.

    Hence, for high precision measurements of the density of a gas, it is important to know the molar polarizability of the gas to high accuracy.

    In this work a GAMOR system has been used to determine the wavelength-dependent molar polarizability of Ar at 1550 nm.  However, a high accuracy assessment of the molar polarizability of a gas requires that the gas density is known with high accuracy. Since this is not trivial to assess, the molar polarizability of argon has been assessed in terms of that of nitrogen, which is assumed to be known with high accuracy. Hence, to minimise measurement errors, the measurement cavity was alternately filled with nitrogen and argon and the ratio between the signals provided by the GAMOR system represents the ratio of the molar polarizabilities of the two gases. It was found that the molar polarizability of argon was  0.94393(5) times that of nitrogen. Since the latter one has been assessed to 4.34828(3) x 10^-6  m^/mol, the molar polarizability of argon could be assessed to 4.10446(5) x 10^-6 m^3/mol.

  • 324. Zakharova, IB
    et al.
    Donenko, EA
    Biryulin, YF
    Sharonova, LV
    Makarova, Tatiana
    Optical and vibrational properties of thin film Fullerene-Zn(II) tetraphenylporphyrin complexes2008In: Fullerenes, nanotubes, and carbon nanostructures (Print), ISSN 1536-383X, E-ISSN 1536-4046, Vol. 16, no 5-6, p. 424-429Article in journal (Refereed)
    Abstract [en]

    In this work a novel material, fullerene-Zn(II) tetraphenylporphyrin, is obtained and studied using UV-Vis-NIR absorption and Raman scattering methods. C-60-ZnTPP thin films were produced by vacuum evaporation in hot-wall reactor. The detection of the A(g2)-derived modes at 1460 and 1452cm(-1) in the Raman spectra manifests the charge-transfer C-60-ZnTPP complex formation. It is shown that additional absorption band at 1.38-1.53 eV observed in the films corresponds to the HOMO-LUMO gap of C-60-ZnTPP complex.

  • 325.
    Zakrisson, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cell shape identification using digital holographic microscopy2015In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, no 24, p. 7442-7448Article in journal (Refereed)
    Abstract [en]

    We present a cost-effective, simple and fast digital holographic microscopy method based upon Rayleigh-Sommerfeld back propagation for identification of the geometrical shape of a cell. The method was tested using synthetic hologram images generated by ray-tracing software and from experimental images of semi-transparent spherical beads and living red blood cells. Our results show that by only using the real part of the back-reconstructed amplitude the proposed method can provide information of the geometrical shape of the object and at the same time accurately determine the axial position of the object under study. The proposed method can be used in flow chamber assays for pathophysiological studies where fast morphological changes of cells are studied in high numbers and at different heights.

  • 326.
    Zhang, Chang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction and Calibration of a Watt Balance2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    We build a calibration system for a Watt balance. The Watt balance uses the Lorentz force acting on a current-carrying coil attached to the weighing pan and placed in a radial magnetic field to balance the gravitational force acting on the measured object. To calibrate the balance, we determine the constant value BL (where B is the total magnetic flux through the coil and L is the total length of the wire around the coil) for the coil A and coil B installed under the weighing pans. We perform two modes of operation to measure BL: velocity mode by applying Faraday's law of induction, and force mode, using magnetic force acting on the coil carrying a current and a set of reference masses.

    We find that BL from the velocity mode for coil A is 4.2±0.2 [(Vs)/m] and 3.9±0.1 [(Vs)/m] for coil B, while from force mode, BL is 3.91±0.04 [(Vs)/m] for coil A and 3.42±0.04 [(Vs)/m] for coil B. Considering the error from reference masses, we use the results of the velocity mode as the most accurate value of BL for the coils.

  • 327.
    Zhang, Hanqing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of an Optical Tweezers Instrumentation and Validation of Brownian motion2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    We constructed a standalone optical trapping system that was steerable in three dimensions and allowed for sufficient imaging of one цm particles with a CCD camera. The motion of the trapped particles was monitored by both a position sensitive detector as well with the CCD camera. The trap stiffness was evaluated by the power spectrum method and the equipartition theorem. For calibration of the stiffness of the trap, we found that the power spectrum method with data assessed by the PSD was most straightforward and accurate. The equipartition method was compromised by noise, low resolution and the bandwidth of the detector. With a HeNe laser run at 10 mW output power the trap strength of our system reached ~2 pN/um. The results also showed a decrease in the trap stiffness and particle's position variance when the size of trapped particles increased.

  • 328.
    Zhang, Hanqing
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stangner, Tim
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Object plane detection and phase retrieval from single-shot holograms using multi-wavelength in-line holography2018In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 57, no 33, p. 9855-9862Article in journal (Refereed)
    Abstract [en]

    Phase retrieval and the twin-image problem in digital in-line holographic microscopy can be resolved by iterative reconstruction routines. However, recovering the phase properties of an object in a hologram requires an object plane to be chosen correctly for reconstruction. In this work, we present a novel multi-wavelength iterative algorithm to determine the object plane using single-shot holograms recorded at multiple wavelengths in an in-line holographic microscope. Using micro-sized objects, we verify the object positioning capabilities of the method for various shapes and derive the phase information using synthetic and experimental data. Experimentally, we built a compact digital in-line holographic microscopy setup around a standard optical microscope with a regular RGB-CCD camera and acquired holograms of micro-spheres, E. coli, and red blood cells, which are illuminated using three lasers operating at 491 nm, 532 nm, and 633 nm, respectively. We demonstrate that our method provides accurate object plane detection and phase retrieval under noisy conditions, e.g., using low-contrast holograms with an inhomogeneous background. This method allows for automatic positioning and phase retrieval suitable for holographic particle velocimetry, and object tracking in biophysical or colloidal research. 

  • 329.
    Zhang, Hui
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Measurement of the emission spectrum from a super luminescent white diode with a Fourier transform spectrometer2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A Fourier transform spectrometer (FTS) was constructed to analyze the light of a white LED. The spectrometer utilizes re-sampling with the help of a reference interferogram from a HeNe laser. The resolution was estimated from the measured line width of the re-sampled HeNe laser and was found to be in the order of 0.4 nm. The spectrum collated from the white diode had a signal to noise ratio of 350 which was more than sufficient for our purposes. The measured spectrum point towards the light being produced by a combination of red and blue LED:s and a phosphor layer of YAG:Ce providing the green-yellow colors.

  • 330.
    Zhang, Wenji
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction and calibration of a Kibble balance2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Kibble Balance is a device that can measure the mass by using the magnetic force acting on a current carrying coil. The aim of this experiment is to construct and calibrate a Kibble balance, and use it to measurements of small masses. A PID-controller written in LabView program is developed to control the balance. The calibration of the balance is done in the velocity mode and the corresponding BL-term is measured BL = 6.5(2)x10-2 (T·m). The linear relation between the mass and the current through the coil is found mass(mg) = 6.2(3) x I (mA) .

  • 331.
    Zhang, Xiaoying
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Design of a Laser Tweezers Set-up and Evaluation of its Stiffness Using the Power Spectrum Method2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Laser tweezers is a method that allows for manipulation of transparent particles in three dimensions by using a focused laser beam. If a spherical particle is trapped it is also possible to measure forces since the trapped particle is confined in a harmonic potential. In this work, we designed a laser tweezers set-up and investigated the forces in a trap using the power spectrum method. With a 0.67 mW power at the focus of the objective we trapped one-micron particles and calibrated the stiffness of the trap in both the x- and y-direction and found the trap stiffness to be 1.0(3) pN/μm and 0.9(2) pN/μm, respectively. This even value shows that our trap is symmetric.

  • 332.
    Zhang, Yujie
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High precision measurements of the evaporation rate of liquids by the use of a Kibble balance2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Kibble balance (previously watt balance) is an electromechanical weight measuring instrument that measures the weight of a test object very precisely by the strength of an electric current and a voltage. The aim of this experiment is to build a working Kibble balance to measure the evaporation rate of a water droplet. In this report, the theoretical basis of the Kibble Balance system including the working principles, Setup, PID controller programming and the calibration method is introduced. In the result part of the report, the coefficient of the coil BL will be given by two kinds of method (velocity mode and force mode). The coefficient given by velocity mode is 6.76(27)x102 T·m and the coefficient given by force mode is 6.77(30)x102 T·m. Both of the modes works well in this experiment. The evaporation rate of a water droplet is -0.11(1) mg/min. Unfortunately, the measurement of the alcohol droplet didn't succeed because the alcohol evaporated very fast and the PID controller was not fast enough to measure.

  • 333.
    Zhao, Gang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China .
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China .
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Differential noise-immune cavity-enhanced optical heterodyne molecular spectroscopy for improvement of the detection sensitivity by reduction of drifts from background signals2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 23, p. 29454-29471Article in journal (Refereed)
    Abstract [en]

    The detection sensitivity of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is often limited by background signals that bring in drifts. A novel realization of NICE-OHMS, termed differential NICE-OHMS, that both reduces such drifts and enlarges the molecular signal is presented. It is based on simultaneous detection of NICE-OHMS signals in reflection and transmission, followed by a subtraction of the former (properly weighted) from the latter. An Allan plot analysis shows that the instrumentation could demonstrate a noise equivalent absorption per unit length (NEAL) of 4.7 × 10−14 cm−1, obtained for an integration time of 170 s.

  • 334.
    Zhao, Gang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shot-noise-limited Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 4, p. 715-718Article in journal (Refereed)
    Abstract [en]

    Shot-noise-limited Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) has been realized by implementation of balanced detection. A characterization of the system based on Allan-Werle plots of the absorption coefficient, retrieved by fitting a model function to data, shows that the system has a white noise equivalent absorption per unit length per square root of bandwidth of 2.3 x 10(-13) cm(-1) Hz(-1/2), solely 44% above the shot noise limit, and a detection sensitivity of 2.2 x 10(-14) cm(-1) over 200 s, both being unprecedented for Db NICE-OHMS. The white noise response follows the expected inverse square root dependence on power that is representative of a shot-noise-limited response, which confirms that the system is shot-noise-limited. 

  • 335.
    Zhao, Gang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Shanxi Univ, Inst Laser Spect, State Key Lab Quantum Opt & Quantum Opt Devices, Taiyuan 030006, Shanxi, Peoples R China; Shanxi Univ, Collaborat Innovat Ctr Extreme Opt, Taiyuan 030006, Shanxi, Peoples R China.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Whispering-gallery-mode laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry2017In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 16, p. 3109-3112Article in journal (Refereed)
    Abstract [en]

    The whispering-gallery-mode (WGM) laser is a type of laser that has an exceptionally narrow linewidth. Noise-immune cavity-enhanced optical heterodyne molecular spectrometry, which is a detection technique with extraordinary properties that benefit from narrow linewidth lasers, has been realized with a WGM laser. By locking to a cavity with a finesse of 55 000, acetylene and carbon dioxide could be simultaneously detected down to an unprecedented noise equivalent absorption per unit length of 6.6 x 10(-14) cm(-1) over 150 s, corresponding to 5 ppt of C2H2.

  • 336.
    Zhao, Gang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ma, Weiguang
    State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High resolution ultra-sensitive trace gas detection by use of cavity-position-modulated sub-Doppler NICE-OHMS - Application to detection of acetylene in human breathManuscript (preprint) (Other academic)
    Abstract [en]

    A sensitive high resolution spectrometer for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species by sub-Doppler (sD) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is presented. The setup is based on a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened (Db) detection. An additional layer of modulation is added to reduce the influence of narrow etalons and improve the sensitivity for sD detection. By dithering synchronously the positions of the two cavity mirrors, the effect of residual etalons between one of the cavity mirrors and another surface in the system could be reduced without affecting the frequencies of the cavity mode. This reduced the drifts in the system, allowing for an Allan deviation of the absorption coefficient of 2.2×10−13 cm−1 for an integration time of 60 s, which, for the targeted C2H2 transition at 6518.4858 cm−1, corresponds to a 3σ detection sensitivity of 130 ppt. Sub-Doppler trace gas detection is demonstrated by measuring ppb levels of C2H2 in the exhaled breath of smokers. A procedure was worked out for simultaneous detection of CO2, based on the Db response. It is shown that despite significant spectral interference from CO2, which precludes Db detection of C2H2 in breath, acetylene could be detected in breath from smokers with good spectral resolution by the use of sD NICE-OHMS.

  • 337.
    Zhao, Gang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China .
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics. National Metrology Institute VTT MIKES, Tekniikantie 1, FI-02044 VTT, Finland.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ma, Weiguang
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-resolution trace gas detection by sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry: application to detection of acetylene in human breath2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 13, p. 17940-17953Article in journal (Refereed)
    Abstract [en]

    A sensitive high-resolution sub-Doppler detecting spectrometer, based on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS), for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species is presented. It is designed around a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened (Db) detection. By synchronous dithering the positions of the two cavity mirrors, the effect of residual etalons between the cavity and other surfaces in the system could be reduced. An Allan deviation of the absorption coefficient of 2.2 × 10-13 cm-1 at 60 s, which, for the targeted transition in C2H2, corresponds to a 3σ detection sensitivity of 130 ppt, is demonstrated. It is shown that despite significant spectral interference from CO2 at the targeted transition, which precludes Db detection of C2H2, acetylene could be detected in exhaled breath of healthy smokers.

  • 338. Zhao, Gang
    et al.
    Tan, Wei
    Hou, Jiajia
    Qiu, Xiaodong
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University ; Collaborative Innovation Center of Extreme Optics, Shanxi University.
    Li, Zhixin
    Dong, Lei
    Zhang, Lei
    Yin, Wangbao
    Xiao, Liantuan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Suotang
    Calibration-free wavelength-modulation spectroscopy based on a swiftly determined wavelength-modulation frequency response function of a DFB laser2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 2, p. 1723-1733Article in journal (Refereed)
    Abstract [en]

    A methodology for calibration-free wavelength modulation spectroscopy (CF-WMS) that is based upon an extensive empirical description of the wavelength-modulation frequency response (WMFR) of DFB laser is presented. An assessment of the WMFR of a DFB laser by the use of an etalon confirms that it consists of two parts: a 1st harmonic component with an amplitude that is linear with the sweep and a nonlinear 2nd harmonic component with a constant amplitude. Simulations show that, among the various factors that affect the line shape of a background-subtracted peak-normalized 2f signal, such as concentration, phase shifts between intensity modulation and frequency modulation, and WMFR, only the last factor has a decisive impact. Based on this and to avoid the impractical use of an etalon, a novel method to pre-determine the parameters of the WMFR by fitting to a background-subtracted peak-normalized 2f signal has been developed. The accuracy of the new scheme to determine the WMFR is demonstrated and compared with that of conventional methods in CF-WMS by detection of trace acetylene. The results show that the new method provides a four times smaller fitting error than the conventional methods and retrieves concentration more accurately.

  • 339. Zhao, Gang
    et al.
    Tan, Wei
    Jia, Mengyuan
    Hou, Jiajuan
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dong, Lei
    Zhang, Lei
    Feng, Xiaoxia
    Wu, Xuechun
    Yin, Wangbao
    Xiao, Liantuan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Suotang
    Intensity-Stabilized Fast-Scanned Direct Absorption Spectroscopy Instrumentation Based on a Distributed Feedback Laser with Detection Sensitivity down to 4 x 10(-6)2016In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 16, no 9, article id 1544Article in journal (Refereed)
    Abstract [en]

    A novel, intensity-stabilized, fast-scanned, direct absorption spectroscopy (IS-FS-DAS) instrumentation, based on a distributed feedback (DFB) diode laser, is developed. A fiber-coupled polarization rotator and a fiber-coupled polarizer are used to stabilize the intensity of the laser, which significantly reduces its relative intensity noise (RIN). The influence of white noise is reduced by fast scanning over the spectral feature (at 1 kHz), followed by averaging. By combining these two noise-reducing techniques, it is demonstrated that direct absorption spectroscopy (DAS) can be swiftly performed down to a limit of detection (LOD) (1 sigma) of 4 x 10(-6), which opens up a number of new applications.

  • 340.
    Zheng, Ningxuan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a Free-Space Frequency Modulated DFB-Laser-Based Radar for Measurement of Distances and Velocities2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Laser radar is a technique to get three-dimensional image information of the surrounding with high precision. Laser radar techniques have been widely studied and improved over the recent years, in particular the frequency modulated (FM) DFB-laser-based lidar. The research in this paper focuses on a implementation for short-distance measurements in the tens of cm range to demonstrate the principles of FM-DFB-laser radar. The performance of the system for distance and velocity measurements was evaluated under various condition. Results of Allan deviation show that the precision for distance measurement is 0.008 mm at the optimum integration time of 0.4 second for 100 Hz 1 V. The precision given by standard deviation of mean for distance measurements is 0.006 mm at 100 Hz 500 mV and 0.001 mm/s for velocity at 10 Hz 500 mV.

  • 341.
    Zhong, Minni
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterization of Vibrational Eigenmodes of Wine Glasses Using a Stroboscope Camera2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The vibrational eigenmodes of wine glasses have been characterized by the use of a stroboscope camera. By matching the frequency of the stroboscope to the resonant frequency of the wineglass, the vibration of the wineglass can be acquired as several frames. And the FFT function in Labview and RGB function in Matlab are used to analyze the detail, which results in lowering the resonant frequency when adding water into the wineglass but with different parameters. It was found that the wineglass investigated had resonant frequency of 414.61 Hz, and that the resonance frequency decreased as a function of the height of liquid.

  • 342.
    Zhou, Shaobin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Comparison of Schlieren photography using different light sources2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Schlieren technique is widely used to visualize the gradient of temperature fields and the gradient of density fields of fluid. The selection of light sources plays an important role. In this experiment, the aim was to compare Schlieren photography using white light, red light and laser by analyzing their ability to visualize the gradient of refractive index. By comparing the Schlieren images that was produced by visualizing static fluid and high speed fluid with a Z-type Schlieren system, we found that laser light had the largest sensitivity to be 1377.4 but the smallest dynamic range in detecting deflection angle to be 3.49 × 10-4 degrees. The red light had the second largest sensitivity to be 490.88 and the second smallest dynamic range to be 4.97 × 10-4  degrees. The white light had the smallest sensitivity to be 224.09 but the largest dynamic range which was 7.96×10-4  degrees.

  • 343. Zhou, Yueting
    et al.
    Liu, Jianxin
    Guo, Songjie
    Zhao, Gang
    Ma, Weiguang
    Cao, Zhensong
    Dong, Lei
    Zhang, Lei
    Yin, Wangbao
    Wu, Yongqian
    Xiao, Lianxuan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Suotang
    Laser frequency stabilization based on a universal sub-Doppler NICE-OHMS instrumentation for the potential application in atmospheric lidar2019In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 12, no 3, p. 1807-1814Article in journal (Refereed)
    Abstract [en]

    Lidar is an effective tool for high-altitude atmospheric measurement in which a weak absorption line for the target gas is selected to ensure a large optical depth. The laser frequency stabilization to the line center is required, and a sub-Doppler (sD) spectroscopy of the target line is preferred as a frequency reference. In this paper, a novel universal sD noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) instrumentation based on a fiber-coupled optical single-sideband electro-optic modulator (f-SSM) for the potential application in atmospheric lidar for different target gases with different types of lasers is reported. The f-SSM can replace all frequency actuators in the system, so as to eliminate the individual design of feedback servos that often are tailored for each laser. The universality of the instrumentation was demonstrated by the alternative use of either an Er-doped fiber laser or a whispering-gallery mode laser. Then the instruments based on both lasers were used to produce the sD signals of acetylene, which worked as a frequency reference to stabilize the laser. By performing the lockings, relative frequency stabilizations of 8.3 x 10(-13) and 7.5 x 10(-13) at an integration time of 240 s were demonstrated.

  • 344.
    Zhu, Jianping
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a Fiber-Coupled Frequency Modulated DFB-Laser-Based Radar for Measurement of Distances and Velocities2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The report describes the realization of the distance and velocity measurement with a fiber coupled frequency modulated continuous wave (FMCW) laser radar. It focuses on FMCW method and discusses the resolution, measurement range and accuracy of different implementations of radar systems.

    For distance measurement, the system with 50 Hz sweep frequency displays the best performance with an absolute error smaller than 1.3 mm over the whole measurement range. The best precision evaluated using the Allan deviation is 0.1 mm at a integration time of 200 ms for a 100 Hz sweep frequency. With higher sweep frequency, the system provides results faster but the measurement range is smaller.

    For velocity measurement, systems with 200 mV amplitude and 500 mV amplitude are always better than that with 1 V amplitude. A lower modulation amplitude shows less influence of residual amplitude modulation but less stability of beat signals.

  • 345. Ögren, Yngve
    et al.
    Sepman, Alexey
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wiinikka, Henrik
    Comparison of measurement techniques for temperature and soot concentration in premixed, small-scale burner flames2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 10, p. 11328-11336Article in journal (Refereed)
    Abstract [en]

    Optical and intrusive measurement techniques for temperature and soot concentration in hot reacting flows were tested on a small-scale burner in fuel-rich, oxygen-enriched atmospheric flat flames produced to simulate the environment inside an entrained flow reactor. The optical techniques comprised two-color pyrometry (2C-PYR), laser extinction (LE), and tunable diode laser absorption spectroscopy (TDLAS), and the intrusive methods included fine-wire thermocouple thermometry (TC) and electrical low pressure impactor (ELPI) particle analysis. Vertical profiles of temperature and soot concentration were recorded in flames with different equivalence and O2/N2 ratios. The 2C-PYR and LE data were derived assuming mature soot. Gas temperatures up to 2200 K and soot concentrations up to 3 ppmv were measured. Close to the burner surface, the temperatures obtained with the pyrometer were up to 300 K higher than those measured by TDLAS. Further away from the burner, the difference was within 100 K. The TC-derived temperatures were within 100 K from the TDLAS results for most of the flames. At high signal-to-noise ratio and in flame regions with mature soot, the temperatures measured by 2C-PYR and TDLAS were similar. The soot concentrations determined with 2C-PYR were close to those obtained with LE but lower than the ELPI results. It is concluded that the three optical techniques have good potential for process control applications in combustion and gasification processes. 2C-PYR offers simpler installation and 2D imaging, whereas TDLAS and LE provide better accuracy and dynamic range without calibration procedures.

4567 301 - 345 of 345
CiteExportLink to result list
Permanent 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