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  • 151. Kolliopoulos, G.
    et al.
    Bergues, B.
    Schröder, H.
    Carpeggiani, P. A.
    Veisz, Laszlo
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Tsakiris, G. D.
    Charalambidis, D.
    Tzallas, P.
    Revealing quantum path details in high-field physics2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 1, article id 013822Article in journal (Refereed)
    Abstract [en]

    The fundamental mechanism underlying harmonic emission in the strong-field regime is governed by tunnel ionization of the atom, followed by the motion of the electron wave packet in the continuum, and finally by its recollision with the atomic core. Due to the quantum nature of the process, the properties of the electron wave packet strongly correlate with those of the emitted radiation. Here, by spatially resolving the interference pattern generated by overlapping the harmonic radiation emitted by different interfering electron quantum paths, we have succeeded in unravelling the intricacies associated with the recollision process. This has been achieved by mapping the spatial extreme-ultraviolet (EUV)-intensity distribution onto a spatial ion distribution, produced in the EUV focal area through the linear and nonlinear processes of atoms. By in situ manipulation of the intensity-dependent motion of the electron wave packets, we have been able to directly measure the difference between the harmonic emission times and electron path lengths resulting from different electron trajectories. Due to the high degree of accuracy that the present approach provides, we have been able to demonstrate the quantum nature of the recollision process. This is done by quantitatively correlating the photoemission time and the electron quantum path-length differences, taking into account the energy-momentum transfer from the driving laser field into the system. This information paves the way for electron-photon correlation studies at the attosecond time scale, while it puts the recollision process from the semiclassical prospective into a full quantum-mechanical context.

  • 152. Kolliopoulos, G.
    et al.
    Tzallas, P.
    Bergues, B.
    Carpeggiani, P. A.
    Heissler, P.
    Schröder, H.
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Charalambidis, D.
    Tsakiris, G. D.
    Single-shot autocorrelator for extreme-ultraviolet radiation2014In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 31, no 5, p. 926-938Article in journal (Refereed)
    Abstract [en]

    A novel single-shot second-order autocorrelation scheme for extreme-ultraviolet radiation (XUV) is proposed. It is based on an ion-imaging technique, which provides spatial information of ionization products in the focal volume of the XUV beam. Using simple analytical and detailed numerical modeling, an evaluation toward selecting an optimum configuration has been performed. The implementation of the concept to characterize attosecond pulses is discussed, and the proposed setups are assessed.

  • 153. Kormin, Dmitrii
    et al.
    Borot, Antonin
    Ma, Guangjin
    Dallari, William
    Bergues, Boris
    Aladi, Mark
    Földes, Istvan B.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Spectral interferometry with waveform-dependent relativistic high-order harmonics from plasma surfaces2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 4992Article in journal (Refereed)
    Abstract [en]

    The interaction of ultra-intense laser pulses with matter opened the way to generate the shortest light pulses available nowadays in the attosecond regime. Ionized solid surfaces, also called plasma mirrors, are promising tools to enhance the potential of attosecond sources in terms of photon energy, photon number and duration especially at relativistic laser intensities. Although the production of isolated attosecond pulses and the understanding of the underlying interactions represent a fundamental step towards the realization of such sources, these are challenging and have not yet been demonstrated. Here, we present laser-waveform-dependent high-order harmonic radiation in the extreme ultraviolet spectral range supporting well-isolated attosecond pulses, and utilize spectral interferometry to understand its relativistic generation mechanism. This unique interpretation of the measured spectra provides access to unrevealed temporal and spatial properties such as spectral phase difference between attosecond pulses and field-driven plasma surface motion during the process.

  • 154. Krivchikov, Alexander I.
    et al.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal Conductivity of Triphenyl Phosphite's Liquid, Glassy, and Glacial States2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 10, p. 2845-2853Article in journal (Refereed)
    Abstract [en]

    The thermal conductivity kappa and heat capacity per unit volume rho C-p of triphenyl phosphite (TPP) were measured under different pressure and temperature conditions, and with time during the sluggish liquid to glacial state transformation at temperatures about 15 K above the glass transition temperature. As the transformation slowly proceeds during several hours, rho C-p decreases monotonically from that of the liquid state to a value close to that of the vitrified state. Concurrently, kappa increases nonmonotonically with an intermediate local maximum followed by a minimum, before the final rise to a higher kappa. The properties of the ultimately formed glacial state depend on the thermal history, which implies that the state formed under these conditions is a heterogeneous mixture of nanocrystals and mainly amorphous-like solid, and that the relative amount and microstructure depend on the conditions of the transformation. The nonmonotonic changes in phonon propagation during the liquid to glacial transformation suggest microstructural changes which are consistent with a liquid-liquid transformation and sluggish growth of nanocrystals within amorphous-like solid domains. The isobaric thermal conductivity of the as-formed glacial state shows a reversible step increase, just prior to crystallization on heating, which deviates from the typical behavior of glasses, liquids, and crystals. An increase in pressure shifts the step to higher temperatures and suppresses crystallization, which reveals another reversible rise in kappa and C-p. These results show that increased molecular mobility in the glacial state increases and suggest reduced thermal resistance at boundaries or that the motions carry heat.

  • 155.
    Kőrös, Csaba Pál
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Field synthesis with sub-cycle features and its application2017Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis we extensively investigated numerically the phenomenon of ω-2ω gas high harmonic generation in Neon with different model calculations, and the second harmonic generation was also theoretically and experimentally examined for better predictions. We carried out experiments in order to determine the maximal conversion efficiency of second harmonic generation: the obtained energy conversion is 14%, what corresponds to ~3% intensity of the fundamental pulse. This corresponds to our SHG-calculations too.

    The ω-2ω GHHG was simulated with different models. Firstly, several 1-atomic calculations were made with the Lewenstein-integral, and with the Saddle-Point Equations. The synchronization and the ratio of the fundamental and the SH pulse were examined in the ω-2ω GHHG. These results formed the basis to the deeper macroscopic simulations.  

    The extended macroscopic scans showed two distinct features of the ω-2ω GHHG. On the one hand, the one-atomic continuum-improvement can be transfered to 15 mbar-pressure gas cells with a precise adjustment. When Zirconium filter was applied, the transform-limited pulse durations could reach 74 as, which is a factor of 3 improvement compared to the GHHG without 2ω field. The exact value expected to be higher depending on the phase-structure of the radiation, which was not examined. On the other hand, when the medium was a high-pressure gas jet, the ionization gated GHHG spectra experienced a drastic amplitude-improvement with the SH field. Thus, while the pulse duration remained nearly the same, the intensity could reach even an 11-fold increment. In this case the transform-limited pulse duration is 66 as. The background of this phenomenon is still not investigated, however it is the first observation of this improvement to our knowledge.

  • 156.
    Lathdavong, Lemthong
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Development of diode laser-based absorption and dispersion spectroscopic techniques for sensitive and selective detection of gaseous species and temperature2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

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

  • 157.
    Lathdavong, Lemthong
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shao, Jie
    Institute of Information Optics of Zhejiang Normal University, Jinhua, China, 321004.
    Kluczynski, Pawel
    Siemens AB, IIA SLA R&D, Box 14153, SE-400 20 Göteborg, Sweden.
    Lundqvist, Stefan
    Siemens AB, IIA SLA R&D, Box 14153, SE-400 20 Göteborg, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Methodology for detection of carbon monoxide in hot, humid media by telecommunication distributed feedback laser-based tunable diode laser absorption spectrometry2011In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 17, p. 2531-2550Article in journal (Refereed)
    Abstract [en]

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

  • 158.
    Lathdavong, Lemthong
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Westberg, Jonas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shao, Jie
    Institute of Information Optics of Zhejiang Normal University.
    Dion, Claude M.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kluczynski, Pawel
    Siemens AB.
    Lundqvist, Stefan
    Siemens AB.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Faraday modulation spectrometry of nitric oxide addressing its electronic X2Π − A2Σ+ band: I. theory2010In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, no 29, p. 5597-5613Article in journal (Refereed)
    Abstract [en]

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

  • 159.
    Lei, Xing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Realization of an optical tweezers set-up and evaluation of its stiffness using the equipartition theorem2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this work was to build and optical tweezers instrument, trap a 1μm particle and calibrate the trapping stiffness. We used an oil- immersion objective to focus a He-Ne laser beam and to visualize the particle we used in a CCD camera. To measure the trapping stiffness, we used a position sensor detector (PSD) and measured the displacement of particle in microfluidic flow chamber, and transformed the motion to a power spectrum. To calibrate the trap, we applied the equipartition method to analyze trapped particles. The result shows that our instrument could trap particles and that its stiffness in x and y direction are 2.5(3) pN/μm and 2.8(3) pN/μm, respectively.

  • 160. Leshchenko, Vyacheslav E.
    et al.
    Kessel, Alexander
    Jahn, Olga
    Krüger, Mathias
    Münzer, Andreas
    Trushin, Sergei A.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
    Major, Zsuzsanna
    Karsch, Stefan
    On-target temporal characterization of optical pulses at relativistic intensity2019In: Light: Science & Applications, ISSN 2095-5545, E-ISSN 2047-7538, Vol. 8, article id 96Article in journal (Refereed)
    Abstract [en]

    High-field experiments are very sensitive to the exact value of the peak intensity of an optical pulse due to the nonlinearity of the underlying processes. Therefore, precise knowledge of the pulse intensity, which is mainly limited by the accuracy of the temporal characterization, is a key prerequisite for the correct interpretation of experimental data. While the detection of energy and spatial profile is well established, the unambiguous temporal characterization of intense optical pulses, another important parameter required for intensity evaluation, remains a challenge, especially at relativistic intensities and a few-cycle pulse duration. Here, we report on the progress in the temporal characterization of intense laser pulses and present the relativistic surface second harmonic generation dispersion scan (RSSHG-D-scan)-a new approach allowing direct on-target temporal characterization of high-energy, few-cycle optical pulses at relativistic intensity.

  • 161. Leshchenko, Vyacheslav E.
    et al.
    Kessel, Alexander
    Jahn, Olga
    Krüger, Mathias
    Münzer, Andreas
    Trushin, Sergei A.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Major, Zsuzsanna
    Karsch, Stefan
    On-target temporal characterization of optical pulses at relativistic intensity2019In: Light: Science & Applications, ISSN 2095-5545, E-ISSN 2047-7538, Vol. 8, article id 96Article in journal (Refereed)
    Abstract [en]

    High-field experiments are very sensitive to the exact value of the peak intensity of an optical pulse due to the nonlinearity of the underlying processes. Therefore, precise knowledge of the pulse intensity, which is mainly limited by the accuracy of the temporal characterization, is a key prerequisite for the correct interpretation of experimental data. While the detection of energy and spatial profile is well established, the unambiguous temporal characterization of intense optical pulses, another important parameter required for intensity evaluation, remains a challenge, especially at relativistic intensities and a few-cycle pulse duration. Here, we report on the progress in the temporal characterization of intense laser pulses and present the relativistic surface second harmonic generation dispersion scan (RSSHG-D-scan)—a new approach allowing direct on-target temporal characterization of high-energy, few-cycle optical pulses at relativistic intensity.

  • 162.
    Li, Qing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterization of vibrational eigenmodes of wine glasses using laser triangulation2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this project, triangulation technique is employed to study the vibrational eigenmodes of wine glasses and determine how the resonance frequency would change when fill the glass with liquid. The profile of the vibrating system turns out to be an elliptical deformation with two nodal diameters, which can be described by ψ(s,Φ ,t)=f(s)cos(17.59t)sin(4586.72t). The experimental result shows that the increasing liquid level contained will lower the resonance frequency without changing the vibrational spectrum. The relation between liquid level and vibrational eigenfrequency is described as ω2= 2.028∗107/(1+2.967(±18)∗10−5∗h5.391(±16)).

  • 163.
    Li, Xiangyan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of Transitions in Iodine Induced by an Orange and a Red Laser2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis, we construct a laser-induced fluorescence (LIF) system around a He-Ne orange laser with a wavelength of 632.8404 nm and a red laser with a wavelength of 612.0295 nm for detection of fluorescence of iodine. Simulating all the possible absorption transition in iodine, we obtain the possible energy levels of the ground X1Σg+  and excited states B3Π0u+. In particular,simulating the corresponding fluorescence emission spectrum and comparing to the calibration spectrum obtained from the experiment, we find that the transition R(78)12←6 iodine excited by the red laser can be well suited for the calibration fluorescence spectrum obtained from the experiment. And for the orange laser, the exact transition from the X1Σg+ to the B3Π0u+ states follows P(44)9←2 .

  • 164.
    Li, Xingda
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a Kibble balance for determination of the evaporative loss in alcohol/water mixtures2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this project was to construct a Kibble balance and to use for determination of the rate of evaporation of alcohol/water mixtures. With the help of a PID controller, we measured the current in the coil balancing the weight of the mixtures that were evaporating in time. For the calibration, we operated the balance in the velocity mode, i.e. measured the velocity and induced voltage of the balance coils, and found the value of the BL term is 0.044(2)T m. Using the local gravitational acceleration as 9.8 m/s2, we find the evaporation rate for methanol, isopropanol, methanol/water mixture in 50/50, isopropanol/watter mixture in 50/50, methanol/isopropanol mixture in 50/50 and distilled water to be 8.5(5)x10-8kg/s, 7.5(4)x10-8 kg/s, 5.2(3)10-8 kg/s, 4.1(2)x10-8kg/s, 6.4(3)x10-8kg/s and 8.9(5)x10-9kg/s respectively.

  • 165.
    Li, Zhiwei
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Digital holographic imaging with plane wavefronts - assessing the diffusing constant of a microparticle2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    We built a digital holographic microscopy (DHM) system with a camera, an objective, lenses, and reconstruction algorithm. Then, we investigated the accuracy by calculating the error of diffusion coefficient of the one-micrometer microspheres from their holograms. By obtaining the position of the particle in x, y axis from the center of the particle images in the holograms and reconstructing the holograms of the particle for its position in the z axis, we got the 3D trajectory of the microspheres to compute the diffusion coefficient. Our calculations show that the diffusion coefficient of the particle to be 5.228 x 10-13, 4.605 x 10-13 and 7.506 x 10-13 m2s-1 for x, y and z axis respectively. While the result of z axis is bigger than the theoretical value, x and y axis have smaller error. The results reveal that DHM method is more easily prone to the systematic error than traditional microscopy.

  • 166.
    Liang, Zhiyong
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Detection of nitric oxide by ultraviolet diode laser absorption spectrometry: Comparison between direct absorption techniques and wavelength modulation spectrometry2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An evaluation of the detectability of a fully diode laser based system for detection of nitric oxide (NO) by different techniques, i.e. direct absorption (DAS), differential direct absorption (DDAS) and wavelength modulation spectroscopy (WMS), in the UV-region is presented. The laser system is targeting a strong electronic transition of NO at wavelengths around 226.6 nm. The system performance and stability has been assessed by measuring its Allan deviation. It has been shown that the sensitivity of WMS is one order of magnitude higher than that of the DAS and DDAS. The WMS 1-σ detectability is as low as 9 ppb∙m, while those for DAS and DDAS are 54 ppb∙m and 120 ppb∙m, respectively.

  • 167.
    Lindahl, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Designing radiation protection for a linear accelerator: using Monte carlo-simulations2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The department of Radiation Sciences at Umeå University has obtained an old linear accelerator, intended for educational purposes. The goal of this thesis was to find proper reinforced radiation protection in an intended bunker (a room with thick concrete walls), to ensure that the radiation outside the bunker falls within acceptable levels. The main method was with the use of Monte Carlo-simulations.

    To properly simulate the accelerator, knowledge of the energy distribution of emitted radiation was needed. For this, a novel method for spectra determination, using several depth dose measurements including off-axis, was developed. A method that shows promising results in finding the spectra when measurements outside the primary beam are included. The found energy spectrum was then used to simulate the accelerator in the intended bunker. The resulting dose distribution was visualized together with 3D CAD-images of the bunker, to easily see in which locations outside the bunker where the dose was high.

    An important finding was that some changes are required to ensure that the public does not receive too high doses of radiation on a public outdoor-area that is located above the bunker. Otherwise, the accelerator is only allowed to be run 1.8 hours per year. A workaround to this problem could be to just plant a thorn bush, covering the dangerous area of radius 3m. After such a measure has been taken, which is assumed in the following results, the focus moves to the radiation that leaks into the accelerator’s intended control room, which is located right outside the bunker’s entrance door.

    The results show that the accelerator is only allowed to be run for a maximum of 6.1 or 3.3 hours per year (depending on the placement of the accelerator in the room), without a specific extra reinforced radiation protection consisting mainly of lead bricks. With the specific extra protection added, the accelerator is allowed to be run 44 or 54 hours per year instead, showing a distinct improvement. However, the dose rate to the control room was still quite high, 13.7 μGy/h or 11.2 μGy/h, compared to the average dose received by someone living in Sweden, which is 0.27 μGy/h. Therefore, further measures are recommended. This is however a worst case scenario, since the leakage spectrum from the accelerator itself was simulated as having the same energy spectrum as the primarybeam at 0.1 % of the intensity, which is the maximum leakage dose according to the specifications for the accelerator. This is probably an overestimation of the intensity. Also, the energy spectra of the leakage is probably of lower energy than the primary beam in at least some directions. Implementing more knowledge of the leak spectra in future work, should therefore result in more allowed run hours for the accelerator.

  • 168.
    Linder, Björn
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The Dirac Equation in the Low Energy Limit2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose of this work is to give an introduction to relativistic quantum mechanics for the electron. First a review of the Dirac equation and its application to a free electron and an electron in an electromagnetic field will be given. In particular the hydrogen atom is studied. The low energy limit and the lowest order corrections to non-relativistic quantum mechanics are investigated. These corrections include, among others, the gyromagnetic ratio of the electron and spin-orbit coupling in the hydrogen atom. The low energy limit will be studied both in the usual Pauli-Dirac representation and by using the Foldy-Wouthuysen transformation. The Pauli-Dirac representation is used to obtain the correction terms for the energy levels in the hydrogen atom. The Foldy-Wouthuysen transformation is applied to obtain the corresponding Hamiltonian corrections to order α4 .

  • 169.
    Lindh, E. Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bilayer Light-Emitting Electrochemical Cells for Signage and Lighting Applications2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Artificial light surrounds us in a manifold of shapes. It is mainly utilized for illumination, but also for graphical communication of complex and evolving messages and information, among other things. It can be generated in different ways with incandescent lamps and fluorescent tubes constituting two common examples. Organic solid state light-generation technologies, which boast advantages such as solution processability, thin and flexible form factors, and large versatility, are modern additions to the field. But regardless of the means of generation, whenever light is to be used to communicate information, as signage or displays, it needs to be patterned. Unfortunately patterning is often complicated and expensive from a fabrication point of view, or renders the devices inefficient. To bridge the gap between present technologies and the need for low-cost and low-complexity patterned light emitters, it is important to develop new device architectures and/or fabrication procedures.

    In this thesis we show that patterned light emission can be attained from solution processable bilayer light-emitting electrochemical cells (LECs), in which the bilayer stack comprises an electrolyte and an organic semiconductor as the first and second layer, respectively. We investigate a subtractive direct-write approach, in which electrolyte is displaced and patterned by the contact motion of a thin stylus, as well as an additive inkjet-patterning technique. Both result in electroluminescent patterns, e.g., light-emitting sketches and microscopic signage with high pixel density. But they can also build macroscopic patterned regions with homogeneous emission depending on the design of electrolyte features. Using an in-operando optical microscopy study we have investigated the operational physics and some limiting factors of the bilayer LECs. More specifically we find that the electrolyte film homogeneity is a key property for high optical quality, and that the emitting region is defined by the location of the interfaces between electrolyte, anode, and organic semiconductor. We observe that the cationic diffusion length is less than one micrometer in our employed organic semiconductors, and rationalize the localized emission by cationic electric double-layer formation at the cathode, and the electronically insulating electrolyte at the anode.

    To date, the presented luminescent signage devices feature high-resolution patterns, in both pixelated and line-art form, and show great robustness in terms of fabrication and material compatibility. Being LECs, they have the potential for truly low-cost solution processing, which opens up for new applications and implementations. However, these first reports on patterned bilayer LECs leave plenty of room for improvements of the optical and electronic characteristics. For instance, if the optoelectronic properties of the devices were better understood, a rational design of microscopic electrolyte features could provide for both more efficient LECs, and for more homogeneous light emission from the patterned regions.

  • 170.
    Lindh, E. Mattias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lundberg, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lanz, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mindemark, Jonas
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Chemistry - Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6970Article in journal (Refereed)
    Abstract [en]

    The light-emitting electrochemical cell (LEC) is functional at substantial active-layer thickness, and is as such heralded for being fit for low-cost and fault-tolerant solution-based fabrication. We report here that this statement should be moderated, and that in order to obtain a strong luminous output, it is fundamentally important to fabricate LEC devices with a designed thickness of the active layer. By systematic experimentation and simulation, we demonstrate that weak optical microcavity effects are prominent in a common LEC system, and that the luminance and efficiency, as well as the emission color and the angular intensity, vary in a periodic manner with the active-layer thickness. Importantly, we demonstrate that high-performance light-emission can be attained from LEC devices with a significant active-layer thickness of 300 nm, which implies that low-cost solution-processed LECs are indeed a realistic option, provided that the device structure has been appropriately designed from an optical perspective.

  • 171.
    Linss, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Automation of single-shot carrier-envelope phase measurement2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Pulsed lasers have become widely used working devices in the last decades. Continues development lead to shorter and shorter pulses and consequently higher and higher peak powers. Especially with mode-locked Ti:Sapphire-lasers it is possible to obtain pulses that contain just a few optical cycles of the carrier frequency. The achievable intensities allowed the observation and examination of various nonlinear optical effects.

    For long pulses usually just the carrier frequency and the temporal shape of the intensity envelope (mainly the pulse duration) are important parameters for describing light-matter-interaction. But the shorter a pulse is the more relevant is the relative phase between the carrier wave and the envelope, the so-called carrier-envelope phase (CEP). The interpretation of nonlinear effects like high-harmonic generation (HHG) or electron acceleration from solids often requires knowledge of the temporal behavior of the electric field (and not just the intensity) in a pulse. That is why in such experiments usually either a CEP-stabilized laser-system is used or the CEP is simultaneously measured and compared to the other results in the evaluation (CEP-tagging).

    One possibility to get single-shot measurements of the CEP is an f-to-2f interferometric setup, that records the interference between an octave spanning fundamental spectrum and its second harmonic with a spectrometer. In the spectrogram CEP-depended fringes can be observed in the region where fundamental and second harmonic are spectrally overlapping. To achieve the necessary spectral bandwidth white-light generation is used to broaden the spectrum. The advantage of the f-to-2f setup is that it can be used to measure the CEP at various positions in the laser system as it can handle quite different pulse energies and durations. It should be noted that an f-to-2f system is not able to determine the absolute value of the CEP, but just the CEP difference to a reference pulse.

    For this thesis a program was developed and tested that automates the acquisition and real-time evaluation of the spectrograms. It will be used to determine the CEP changes in different parts of the LWS-20 laser system, particularly for assessing the quality of CEP-stabilization.

  • 172. Liu, Jianxin
    et al.
    Zhou, Yueting
    Guo, Songjie
    Hou, Jiajuan
    Zhao, Gang
    Ma, Weiguang
    Wu, Yongqian
    Dong, Lei
    Zhang, Lei
    Yin, Wangbao
    Xiao, Liantuan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Suotang
    A novel methodology to directly pre-determine the relative wavelength response of DFB laser in wavelength modulation spectroscopy2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 2, p. 1249-1261Article in journal (Refereed)
    Abstract [en]

    A novel methodology to directly pre-determine the relative wavelength response (RWR) of a DFB laser, in terms of a combined current linearly scanned wavelength response and current modulated wavelength response (CMWR), in wavelength modulation spectroscopy (WMS) is presented. It is shown that the assessed RWR can be used to mimic the measured response with standard deviation of discriminations that are below 3.4 x 10(-3)cm(-1) under a variety of conditions. It is also shown that its performance supersedes two commonly used assessment models of the CMWR but is slightly worse than that of the third model. however with the benefit of solely using a single fitting parameter (the concentration) instead of more. When the novel method is applied to the assessment of CO2 concentration in a Herriot-type multipass cell by using the technique of calibration-free WMS, the results show that there is virtually no difference compared to that by use of the best of the other methods. It is concluded that the novel method is more robust and simplifies the retrieval process of gas concentration.

  • 173.
    Liu, Jun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Digital holographic imaging with plane wavefronts – assessing the diffusing constant of a microparticle2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Digital holographic microscopy is a useful tool to realize 3D particles tracking. In this work, we build an in-line holographic microscopy based on plane wave and record videos of the freely diffusing polystyrene particles. We used a tracking algorithm to determine the position and trajectory of particles with the diameter of 2±0.2μm each frame. From this trajectory, we obtained the diffusion coefficient of the particles in the x, y and z-direction, which were assessed to 1.868±0.038e-13 m2/s, 2.552±0.026e-13 m2/s and 0.851±1.045e-10 m2/s, respectively. Moreover, we wrote a MATLAB program to simulate Brownian motion of particles and discussed it with experimental results. The theorical and experimental values are basically same in the x and y-direction, but there is a large deviation in the z-direction.

  • 174.
    Liu, Yanxin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Realization of an optical tweezers set-up and evaluation of its stiffness using the power spectrum method2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of the work was to build an optical tweezers and evaluate its trapping stiffness using power spectrum method. In our work, a single beam optical tweezers system was constructed by using an inverted optical microscope system and then focusing light from a He-Ne laser with an objective with a high numerical aperture. Our setup can trap and manipulate polystyrene particles in three dimensions. We used this system to trap the polystyrene particles with diameters of 1μm in water. To measure the movements of the trapped particles we used a two-dimensional position sensitive detector (PSD) which we calibrated using the power spectrum method. The stiffness of the trap are 1.2(1) pN/μm and 1.4(2) pN/μm in the X and Y direction, respectively.

  • 175. Lotscher, Lauryna
    et al.
    Vamos, Lenard
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Apolonski, Alexander
    Long-term Stability of Nonlinear Pulse Compression using Solid-core Large-mode-area Fibers2015In: Journal of Lasers, Optics & Photonics, ISSN 2469-410X, Vol. 2, no 3, article id 1000124Article in journal (Refereed)
    Abstract [en]

    Long-term stability of a laser system is crucially important for applications such as ultrafast laser spectroscopy. Unfortunately, this topic received little attention in novel pulse compression schemes. Through the ultra-stable beam pointing of the 50 kHz laser system, the long-term stability of nonlinear pulse compression (NPC) was measured for up to 17 hours at different peak powers in a fiber core. The required spectral broadening was achieved in largemode- area photonic-crystal-fibers with linearly and circularly polarized light. The optimal parameters of a NPC system operating close to the fundamental limit of the critical self-focusing peak power were found. A further compression to sub-10 fs pulses in a second fiber stage is also discussed.

  • 176.
    Lu, Chuang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vieira, Francisco Senna
    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.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Near-Infrared Continuous-Filtering Vernier Spectroscopy in a Flame2019In: Conference on Lasers and Electro-Optics, IEEE, 2019, article id SM2N.5Conference paper (Refereed)
    Abstract [en]

    A continuous-filtering Vernier spectrometer based on an Er:fiber femtosecond laser was developed to acquire broadband H2O and OH spectra in a premixed CH4/air flame with 25 ms time resolution and percent precision on concentrations retrieval.

  • 177.
    Lu, Chuang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vieira, Francisco Senna
    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.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Time-resolved continuous-filtering Vernier spectroscopy of H2O and OH radical in a flame2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 21, p. 29521-29533Article in journal (Refereed)
    Abstract [en]

    We use broadband near-infrared continuous-filtering Vernier spectroscopy (CF-VS) for time-resolved detection of H2O and OH radical in a premixed CH4/air flat flame. The CF-VS spectrometer is based on a femtosecond Er:fiber laser, an external cavity that contains the flame, and a detection system comprising a rotating diffraction grating and photodetectors. Spectra of H2O and OH radical around 1570 nm are continuously recorded with 6.6 GHz spectral resolution, 4.0 x 10-7 cm-1 absorption sensitivity, and 25 ms time resolution, while the fuel-air equivalence ratio is periodically modulated with a square wave. The concentrations of the two analytes are retrieved with percent level precision by a fit of a Vernier model to each spectrum spanning 13 nm. The temporal profiles of both concentrations in each modulation cycle are repeatable and the steady-state concentration levels are in good agreement with predictions based on one-dimensional simulations of a static flat flame. The robust CF-VS spectrometer opens up for quantitative monitoring of multiple products of time-varying combustion processes with relatively simple data acquisition procedures.

  • 178.
    Lu, Shuaibing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a Watt balance that is calibrated by the use of a silicon photodetector2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this experiment, we build a Watt balance that uses a silicon photodetector and a HeNe laser beam to measure the position of the weighting pans. The Watt balance is built using a laboratory balance and two coils attached to the pans are positioned in a magnetic field of two magnets. The signals are collected using LabView program, Ni acquisition board, and Agilent measurement unit. The balance allows us to measure masses using current, without the need of calibrated masses. We have calibrated the balance obtaining the coil B value of BL=4.83 Vs/m, and measured masses from 5 mg to 300 mg. For the masses, we measured that the accuracy is 1.2% as compared with the true masses.

  • 179.
    Lundh, Emil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mott transition in anharmonic confinement2008In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 46, no 3, p. 517-520Article in journal (Refereed)
    Abstract [en]

    Two effects are identified that affect the visibility of the Mott transition in an atomic gas in an optical lattice confined in a power-law potential. The transition can be made more pronounced by increasing the power law, but at the same time, experimental uncertainty in the number of particles will induce corresponding fluctuations in the measured condensate fraction. Calculations in two dimensions indicate that a potential slightly more flat-bottomed than a quadratic one is to be preferred for a wide range of particle number fluctuation size.

  • 180.
    Lundh, Emil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mott-insulator dynamics2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 3, p. 6-Article in journal (Refereed)
    Abstract [en]

    The hydrodynamics of a lattice Bose gas in a time-dependent external potential is studied in a mean-field approximation. The conditions under which a Mott insulating region can melt, and the local density can adjust to the new potential, are determined. In the case of a suddenly switched potential, it is found that the Mott insulator stays insulating and the density will not adjust if the switch is too abrupt. This comes about because too rapid currents result in Bloch oscillation-type current reversals. For a stirrer moved through a Mott insulating cloud, it is seen that only if the stirrer starts in a superfluid region and the velocity is comparable to the time scale set by the tunneling will the Mott insulator be affected.

  • 181.
    Lundh, Emil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rammer, Jörgen
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Effective action approach to a trapped Bose gas2002In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 66, no 3, p. 033607-12 pArticle in journal (Refereed)
    Abstract [en]

    The effective-action formalism is applied to a gas of bosons. The equations describing the condensate and the excitations are obtained using the loop expansion for the effective action. For a homogeneous gas, the expansion in terms of the diluteness parameter is identified in terms of the loop expansion. The loop expansion and the limits of validity of the well-known Bogoliubov [J. Phys. (Moscow) 11, 23 (1947)] and Popov, (Zh. Éksp. Teor. Fiz. 47, 1759 (1964) [Sov. Phys. JETP 20, 1185 (1965)]) equations are examined analytically for a homogeneous dilute Bose gas and numerically for a gas trapped in a harmonic-oscillator potential. The expansion to one-loop order, and hence the Bogoliubov equation, is shown to be valid for the zero-temperature trapped gas as long as the characteristic length of the trapping potential exceeds the s-wave scattering length.

  • 182.
    Lundow, Per-Håkan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Markström, Klas
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    The scaling window of the 5D Ising model with free boundary conditions2016In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 911, p. 163-172Article in journal (Refereed)
    Abstract [en]

    The five-dimensional Ising model with free boundary conditions has recently received a renewed interest in a debate concerning the finite-size scaling of the susceptibility near the critical temperature. We provide evidence in favour of the conventional scaling picture, where the susceptibility scales as L-2 inside a critical scaling window of width 1/L-2. Our results are based on Monte Carlo data gathered on system sizes up to L = 79(ca. three billion spins) for a wide range of temperatures near the critical point. We analyse the magnetisation distribution, the susceptibility and also the scaling and distribution of the size of the Fortuin-Kasteleyn cluster containing the origin. The probability of this cluster reaching the boundary determines the correlation length, and its behaviour agrees with the mean field critical exponent delta = 3, that the scaling window has width 1/L-2.

  • 183. Ma, Guangjin
    et al.
    Dallari, William
    Borot, Antonin
    Krausz, Ferenc
    Yu, Wei
    Tsakiris, George D.
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Intense isolated attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 3, article id 033105Article in journal (Refereed)
    Abstract [en]

    We have performed a systematic study through particle-in-cell simulations to investigate the generation of attosecond pulse from relativistic laser plasmas when laser pulse duration approaches the few-cycle regime. A significant enhancement of attosecond pulse energy has been found to depend on laser pulse duration, carrier envelope phase, and plasma scale length. Based on the results obtained in this work, the potential of attaining isolated attosecond pulses with ∼100 μJ energy for photons >16 eV using state-of-the-art laser technology appears to be within reach.

  • 184. Ma, Guangjin
    et al.
    Yu, Wei
    Yu, M. Y.
    Shen, Baifei
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Intense circularly polarized attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 9, p. 10057-10065Article in journal (Refereed)
    Abstract [en]

    We have investigated the polarization of attosecond light pulses generated from relativistic few-cycle laser pulse interaction with the surface of overdense plasmas using particle-in-cell simulation. Under suitable conditions, a desired polarization state of the generated attosecond pulse can be achieved by controlling the polarization of the incident laser. In particular, an elliptically polarized laser pulse of suitable ellipticity can generate an almost circularly polarized attosecond pulse without compromising the harmonic generation efficiency. The process is thus applicable as a new tabletop circularly-polarized XUV radiation source for probing attosecond phenomena with high temporal resolution.

  • 185.
    Ma, Jingxu
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spectroscopic Characterization of Iodine and Assessment of Excitation Transitions Induced by an Orange and a Yellow HeNe Laser2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this paper is to investigate and assess the energy structure of the iodine molecule and assess the exact excitation transitions in I2 that two given fix-frequency HeNe lasers (an "orange" and a "yellow") induce. We assemble a suitable optical system for fluorescence detection of iodine in a glass cell induced by HeNe laser. By comparing the wavelength of the laser, we obtained the possible energy levels of the singlet ground state X 1Σg+  and excited triplet state B 3Π0+u. We model and simulate possible excitation routes, and then compare with the spectrum measured with a spectrometer after calibration of the wavelength scale. We find that the transition R (205) 18←2 is induced by yellow laser and the transition R (46) 154←2 is induced by orange laser.

  • 186.
    Ma, Ruimao
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Comparison of different realizations of Schlieren photography2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Schlieren photography is a technique used to visualize variations in index of refractive in gaseous media. To compare different configurations of Schlieren photography, four kinds of Schlieren setups were constructed in this experiment. As the basis of comparison, their sensitivities were measured and Schlieren images were obtained which were used as a tool to study the temperature gradient of the burning candle. It was found that the Single mirror system had the highest sensitivity but the Schlieren images obtained by Z-type system showed the best quality measuring to visualize temperature gradient. Limited by the requirement of large size and good quality convex lens, the Single-field-lens system and the Dual-field-lens system did not perform equally well.

  • 187.
    Ma, Weiguang
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Theoretical description of Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectroscopy under optically saturated conditions2008In: Journal of the Optical Society of America B, Vol. 25, no 7, p. 1144-1155Article in journal (Refereed)
    Abstract [en]

    A theoretical description of Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) under optically saturated conditions is presented. Expressions for the strength and shape of the Doppler-broadened NICE-OHMS signals are given for both absorption and dispersion phase, in the Voigt regime as well as in the Doppler limit. It is shown that Doppler-broadened NICE-OHMS is affected less by optical saturation than other cavity enhanced techniques; in the Doppler limit the absorption signal decreases by a factor of (1+G+-1)-1/2, where G+-1 is the degree of saturation for one of the frequency modulation sidebands, whereas the dispersion signal is virtually unaffected by optical saturation. In the Voigt regime both signals show additional dependence on optical saturation. The concept of saturation-insensitive detection is introduced and its conditions are identified.

  • 188.
    Ma, Weiguang
    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 030006, China.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Doppler-broadened NICE-OHMS beyond the cavity-limited weak absorption condition – I. Theoretical Description2016In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 168, p. 217-244Article in journal (Other academic)
    Abstract [en]

    Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is conventionally described by an expression (here referred to as the CONV expression) that is restricted to the case when the single-pass absorbance, α0L, is much smaller than the empty cavity losses, π/F [here termed the conventional cavity-limited weak absorption (CCLWA) condition]. This limits the applicability of the technique, primarily its dynamic range and calibration capability. To remedy this, this work derives extended descriptions of Db NICEOHMS that are not restricted to the CCLWA condition. First, the general principles of Db NICEOHMS are scrutinized in some detail. Based solely upon a set of general assumptions, predominantly that it is appropriate to linearize the Beer–Lambert law, that the light is modulated to a triplet, and that the Pound–Drever–Hall sidebands are fully reflected, a general description of Db NICE-OHMS that is not limited to any specific restriction on α0L vs. π/F, here referred to as the FULL description, is derived. However, this description constitutes a set of equations to which no closed form solution has been found. Hence, it needs to be solved numerically (by iterations), which is inconvenient. To circumvent this, for the cases when α0Loπ/F but without the requirement that the stronger CCLWA condition needs to be fulfilled, a couple of simplified extended expressions that are expressible in closed analytical form, referred to as the extended locking and extended transmission description, ELET, and the extended locking and full transmission description, ELFT, have been derived. An analysis based on simulations validates the various descriptions and assesses to which extent they agree. It is shown that in the CCLWA limit, all extended descriptions revert to the CONV expression. The latter one deviates though from the extended ones for α0L around and above 0.1π/F. The two simplified extended descriptions agree with the FULL description for a larger range of α0L than the CONV expression, viz. for the ELET description for α0L up to 0.3π/F and for ELFT for α0L up to 0.6 or 1.0 π/F (depending on the mode of detection). It is then demonstrated that the conventional view of Db NICE-OHMS, which states that the out-of-phase and the in-phase signals can be referred to as a pure absorption and dispersion signal, respectively, breaks down when the CCLWA condition does not hold. In this case, the out-of-phase signal is additionally affected by the phase shifts of the laser components (i.e. dispersion) while the in-phase signal is also influenced by their attenuation. Access to new descriptions broadens considerably the dynamic range of Db NICE-OHMS and facilitates calibration using standard references samples, and thereby its applicability

  • 189.
    Mai, Jing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a Watt balance that is calibrated by the use of a position sensitive detector2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    We have constructed a Watt balance using a laboratory balance and HeNe laser. The balance is calibrated using a position sensitive detector and allows measurements of the absolute mass without the need of calibrated masses. The signals are measured using National Instruments data acquisition board, Agilent measuring unit, and a LabView program. We have performed test measurements of masses in the range from 5 mg to 300 mg. We find that the accuracy of the Watt balance is 3% and that it is limited by the mechanical stability of the laboratory optical table, measurement of the distance and position of the laser beam, and the current measured in the amperometer.

  • 190. Major, B.
    et al.
    Rivas, D. E.
    Bergues, B.
    Weidman, M.
    Muschet, A.
    Schröder, H.
    Korös, Cs. P.
    Balogh, E.
    Kovacs, K.
    Tosa, V.
    Krausz, F.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany .
    Varju, K.
    Investigation of high harmonic generation using a high-power, 5-fs laser in a loose-focusing geometry2017In: 2017 Conference on Lasers and Electro-Optics Europe &  European Quantum Electronics Conference (CLEO/Europe-EQEC), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Summary form only given. Since its first observation almost three decades ago high-order harmonic generation (HHG) in gases became a reliable source of extreme ultraviolet (XUV) pulses, which gave the possibility to study electronic processes on their natural timescale [1, 2]. While the main building blocks of the experimental setups for gas HHG are the same in almost all cases, the focusing or medium geometry varies from realization to realization based on, for example, the available laser power [3, 4].In this work we study HHG in a loose focusing geometry by focusing a ~50-mm diameter (FWHM) beam with a mirror of 16-m focal length (f-number ~320). The main subject of this analysis is to compare low pressure - long interaction length (few millibars and tens of centimeters) with high pressure - short medium (hundreds of millibars and a few millimeters) scenarios and understand the underlying reasons for the observed XUV radiation parameters. The experiments are carried out with on target 35 mJ, sub-5 fs, 740 nm central wavelength pulses provided by an optical parametric synthesizer [5], producing high-energy pulses at the 100 eV spectral region [6]. The theoretical analysis is performed by simulation code based on a three-dimensional nonadiabatic model [7,8]. The good agreement between the experimental and simulation data (see Fig. 1) allows us to use the theoretical findings to gain better insight on the exact phase-matching processes providing the observed features. This detailed description is used to draw general conclusions of the high-harmonic generation process.

  • 191.
    Makela, Harri
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, M.
    Zelan, M.
    Lundh, Emil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stability of nonstationary states of spin-1 Bose-Einstein condensates2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 4, p. 043646-Article in journal (Refereed)
    Abstract [en]

    The stability of nonstationary states of homogeneous spin-1 Bose-Einstein condensates is studied by performing Bogoliubov analysis in a frame of reference where the state is stationary. In particular, the effect of an external magnetic field is examined. It is found that a nonzero magnetic field introduces instability in a (23)Na condensate. The wavelengths of this instability can be controlled by tuning the strength of the magnetic field. In a (87)Rb condensate this instability is present already at zero magnetic field. Furthermore, an analytical bound for the size of a stable condensate is found, and a condition for the validity of the single-mode approximation is presented. Realization of the system in a toroidal trap is discussed, and the full time development is simulated.

  • 192.
    Marklund, Mattias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ilderton, Anton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lundin, Joakim
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Probing new physics using high-intensity laser systems2011In: DIODE-PUMPED HIGH ENERGY AND HIGH POWER LASERS ELI: ULTRARELATIVISTIC LASER-MATTER INTERACTIONS AND PETAWATT PHOTONICS AND HIPER: THE EUROPEAN PATHWAY TO LASER ENERGY / [ed] Hein, J; Silva, LO; Korn, G; Gizzi, LA; Edwards, C, SPIE - International Society for Optical Engineering, 2011, article id 80801HConference paper (Refereed)
    Abstract [en]

    Current high-intensity laser sources offer a multitude of research, experiment and application possibilities, ranging from e. g. ionisation studies of atomic and molecular systems to particle acceleration for medical purposes. Planned upgrades of existing laser sources will further increase the deliverable intensities and make certain low-intensity (as compared to the Schwinger field) tests of quantum electrodynamics viable. Moreover, secondary sources of radiation, and planned future facilities, offer several-orders-of-magnitude increases in intensities. Thus, it is highly relevant to ask what kind of physics that may be probed using future light sources.

  • 193. Maslowski, P.
    et al.
    Kowzan, G.
    Charczun, D.
    Lisak, D.
    Trawinski, R.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lee, K. F.
    Fermann, M. E.
    Optical Frequency Comb Spectroscopy for Gas Metrology and Trace Gas Detection2017In: 2017 Conference on lasers and electro-optics (CLEO), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    We report recent developments of comb-based broadband absorption spectroscopy. The comb-line resolving approaches and Fourier transform spectroscopy with sub-nominal resolution overcome the frequency resolution limits of conventional techniques. Advantages for various applications will be discussed.

  • 194. Maslowski, Piotr
    et al.
    Lee, Kevin F.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kowzan, Grzegorz
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mills, Andrew A.
    Mohr, Christian
    Jiang, Jie
    Fermann, Martin E.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Surpassing the path-limited resolution of Fourier-transform spectrometry with frequency combs2016In: Physical Review A, ISSN 2469-9926, Vol. 93, no 2, article id 021802Article in journal (Refereed)
    Abstract [en]

    We overcome the resolution limit of Fourier-transform spectrometry and measure instrumental line-shape-free broadband molecular spectra with lines narrower than the optical path-limited resolution. We do this by using an optical frequency comb and precisely matching the maximum delay range of the spectrometer to the comb line spacing to measure the intensities of the individual comb lines. This method allows measurements of undistorted high-resolution spectra with acquisition time and interferometer length reduced by orders of magnitude and with frequency scale accuracy given by the comb.

  • 195. Matoussi, A.
    et al.
    Ben Nasr, F.
    Salh, Roushdey
    Physics Department, University of Rostock, Universitatsplatz 3, D-1805 Rostock, Germany.
    Boufaden, T.
    Guermazi, S.
    Fitting, H.-J.
    Eljani, B.
    Fakhfakh, Z.
    Morphological, structural and optical properties of GaN grown on porous silicon/Si(100) substrate2008In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 62, p. 515-519Article in journal (Refereed)
  • 196. Metsälä, Markus
    et al.
    Schmidt, Florian M.
    University of Helsinki.
    Skytta, Mirva
    Vaittinen, Olavi
    Halonen, Lauri
    Acetylene in breath: background levels and real-time elimination kinetics after smoking2010In: Journal of Breath Research, ISSN 1752-7155, E-ISSN 1752-7163, Vol. 4, no 4, article id 046003Article in journal (Refereed)
    Abstract [en]

    We have measured the acetylene concentration in the exhaled breath of 40 volunteers (31 non-smokers, nine smokers) using near-infrared cavity ring-down spectroscopy. The acetylene levels were found to be the same as in ambient air for non-smokers, whereas elevated levels were observed for smokers. Real-time measurements with sub-second time resolution have been applied to measure the elimination kinetics of acetylene in breath after exposure to tobacco smoke. Three exponential time constants can be distinguished from the data and these can be used to define the residence times for different compartments, according to the multi-compartment model of the human body.

  • 197.
    Miao, Jie
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fiber-coupled coherent laser radar for measurement of distance and velocity2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this project was to build a DFB-laser-based frequency-modulated laser radar and use it to measure a distance and velocity of a moving object. The distance and velocity measurements were found to follow the theoretical values. The radar position measurement resolution was 0.021 mm, in some range, and the velocities measurement resolution was 0.001 mm/s. Also, we can get the most stable working time is about 200s. The main source of uncertainty were instabilities of the sweep frequency causing the beat frequency to be not stable.

  • 198.
    Mossegård, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Insight into the water oxidation mechanism on nickel hydroxide electrocatalysts: Density Functional Theory calculations and Electrochemical experiments2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Hydrogen production is an interesting way to store solar energy and to diversify the range of applications for indirect solar power. A promising production method is to use electric power from solar photovoltaic cells to split water in an electrolysis setup. To efficiently run such a setup, one must however have an efficient catalytic material on the two electrodes. This work presents a study of a catalytic material for the oxygen evolution electrode; nickel hydroxide.

    The study is performed both experimentally and theoretically. In the experimental part, an electrode material was synthesized by growing nitrogen doped carbon nanotubes (NCNTs) on a carbon paper (CP) and then decorating the NCNTs with the catalytic material. Scanning electron microscopy (SEM) images of the electrode material showed that the NCNTs were individually coated with a spiky nickel hydroxide nanostructure, with a very large surface area.

    Electrodes with both as-prepared catalytic material and catalytic material first treated in an alkaline solution were then tested in a three-electrode electrolysis setup, in alkaline conditions. It was found that the overpotential for onset of the oxygen evolution reaction (OER) was roughly 0.27 V, which is in the range of previous reports. In contradiction to other reports, the data of this work however indicated that aging the catalytic material decreased its activity and hence that the phase often stated as the more active, was in fact the less active phase. The overall efficiency of the electrodes was found to be low, most likely due to overloading of active material in the electrode structure.

    The theoretical part of the work focused on using Density Functional Theory (DFT) simulations to analyze the OER pathway on three different surfaces of the catalytic material. To simulate the effect of an alkaline environment these surfaces were also passivated with hydroxyl groups in some of the simulations. The lowest overpotential for OER onset found in the calculations was 0.68 V. The calculations further showed that, for the pathways with the smallest overpotentials, the limiting reaction step was a step where an adsorbed hydroxyl group was deprotonated by a hydroxide ion from the solution and oxidized to an adsorbed oxygen atom.

    In addition, the calculations also indicated that passivation of the surfaces had the important effect of lowering the overpotentials for two of the three studied surfaces. 

  • 199. Nilsen, Halvor M.
    et al.
    Lundh, Emil
    Umeå University, Faculty of Science and Technology, Department of Physics. Centre of Mathematics for Applications, P.O. Box 1053 Blindern, NO-0316 Oslo, Norway.
    Splitting dynamics of doubly quantized vortices in Bose-Einstein condensates2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 77, article id 013604Article in journal (Refereed)
    Abstract [en]

    We study the nonlinear dynamics of the splitting of a doubly quantized vortex in a trapped Bose-Einstein condensate. The dynamics is studied in detail by solving the Gross-Pitaevskii equation. The main dynamical features are explained in terms of a nonlinear three-level system, to which we find an analytical solution. This result is compared to linear Bogoliubov analysis and to the full numerical time evolution. It is concluded that the time scale for the splitting is mainly determined by the instability of the linearized system, and nonlinear effects contribute logarithmically.

  • 200.
    Norén, Edvin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Simultaneous detection of potassium, water vapor and temperature with tunable diode laser absorption spectroscopy2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Existing tunable diode laser absorption spectroscopy (TDLAS) sensors for potassium (K) and for water vapor (H2O) and temperature were combined to enable simultaneous measurements in combustion and gasification processes. In-situ real-time detection of the above mentioned combustion parameters will improve the understanding of ash-formation during thermochemical conversion of biomass. Simultaneous measurements facilitate the experimental procedure and decrease the methodological uncertainty introduced by the heterogeneous nature of the pellets. The K sensor is based on direct absorption spectroscopy (DAS), whereas the H2O system employs wavelength modulation spectroscopy (WMS) together with two-line thermometry for temperature assessment. Two methods for combining the laser beams were evaluated, the first involving dichroic elements, the second using available fiber optic combiners. The latter method was considered advantageous. An existing LabVIEW program was modified to allow for simultaneous signal generation and data acquisition for both sensors. The sensors were then tested separately in a low pressure K cell and in ambient air. The combined sensor was applied to simultaneous measurements above various pelletized biofuels during combustion in a single pellet reactor (SPR). Significant difference in absolute concentration and time histories were observed between fuels, in particular for K and temperature. Significant K concentrations were only observed during the devolatilization phase. The combined sensor will be useful in fundamental combustion research.

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