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  • 1.
    Abd Alrahman, Chadi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Khodabakhsh, Amir
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Qu, Zhechao
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Cavity-enhanced optical frequency comb spectroscopy of high-temperature H2O in a flame2014Ingår i: Optics Express, E-ISSN 1094-4087, Vol. 22, nr 11, s. 13889-13895Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate near-infrared cavity-enhanced optical frequency comb spectroscopy of water in a premixed methane/air flat flame. The detection system is based on an Er:fiber femtosecond laser, a high finesse optical cavity containing the flame, and a fast-scanning Fourier transform spectrometer (FTS). High absorption sensitivity is obtained by the combination of a high-bandwidth two-point comb-cavity lock and auto-balanced detection in the FTS. The system allows recording high-temperature water absorption spectra with a resolution of 1 GHz and a bandwidth of 50 nm in an acquisition time of 0.4 s, with absorption sensitivity of 4.2 x 10 (9) cm(-1) Hz(-1/2) per spectral element.

  • 2.
    Abdollahi, Elham
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Development of breath sampling system for detection of exhaled nitric oxide by Faraday modulation spectroscopy2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Technological developments over the years have resulted in many different techniques for detection of nitric oxide (NO) in both the atmosphere and from biological sources. One such technique is Faraday Modulation Spectroscopy (FAMOS), which is a laser-based spectroscopic technique for detection of paramagnetic molecules in gas phase. The technique uses a modulated magnetic field that introduce rotation of the polarization plane of linearly polarized laser light, which can be related to the concentration of the molecules. This enables sensitive and selective detection of paramagnetic gaseous compounds and the technique is thus well suited for detection of NO for biomedical applications in low concentrations which is essential for breath analysis.

    In this thesis, a system for breath analysis is developed and coupled to a Faraday modulation spectrometer for sensitive detection of NO at 5.33 μm based on a room temperature continuous wave distributed feedback (DFB) QCL. It also provides a theoretical model of FAMOS utilizing the most sensitive Q3/2 (3/2 ) transition in NO. The results from this study indicate that the mid-infrared FAMOS system, which was built around a continuous wave (cw) quantum cascade laser (QCL) emitting light with an output power of approximately 70 mW, is fully capable of detection of ppb levels of NO in exhaled human breath.

  • 3.
    Abdollahi, Elham
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Realization of an instrumentation for detection of acetylene in breath by the NICE-OHMS technique2014Självständigt arbete på avancerad nivå (masterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Measurement is an important activity in nearly all branches of science and technology. A measurement technique provides an observer with a numerical value corresponding to the variable being measured. Researchers envision that laser spectroscopy will serve as a functional tool for measurement to detect molecules in gas phase. One such a laser spectroscopic technique for measurement is noise-immune cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS), which is a highly sensitive laser-based spectroscopic technique for detection of molecules in gas phase. The technique was developed in the mid-1990s at the Joint Institute for Laboratory Astrophysics (JILA).

    In this thesis, a realization of instrumentation for detection of acetylene in breath by a fiber laser-based NICE-OHMS instrumentation working in the near-infrared wavelength region is obtained. The results of this study show that the NICE-OHMS system is fully capable of detection of parts-per-billion (ppb) levels of acetylene in exhaled human breath.

  • 4.
    Ako, Thomas
    et al.
    Laboratory of Photonic and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology, Electrum 229, Kista, Sweden.
    Yan, Min
    Laboratory of Photonic and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology, Electrum 229, Kista, Sweden.
    Qiu, Min
    Laboratory of Photonic and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology, Electrum 229, Kista, Sweden.
    Design of invisibility cloaks with an open tunnel2010Ingår i: Optics Express, E-ISSN 1094-4087, Vol. 18, nr 26, s. 27060-27066Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we apply the methodology of transformation optics for design of a novel invisibility cloak which can possess an open tunnel. Such a cloak facilitates the insertion (retrieval) of matter into (from) the cloak’s interior without significantly affecting the cloak’s performance, overcoming the matter exchange bottleneck inherent to most previously proposed cloak designs. We achieve this by applying a transformation which expands a point at the origin in electromagnetic space to a finite area in physical space in a highly anisotropic manner. The invisibility performance of the proposed cloak is verified by using full-wave finite-element simulations.

  • 5. Aladi, M.
    et al.
    Bolla, R.
    Cardenas, D. E.
    Veisz, László
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Foldes, I. B.
    Cluster size distributions in gas jets for different nozzle geometries2017Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 12, artikel-id C06020Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cluster size distributions were investigated in case of different nozzle geometries in argon and xenon using Rayleigh scattering diagnostics. Different nozzle geometries result in different behaviour, therefore both spatial- and temporal cluster size distributions were studied to obtain a well-characterized cluster target. It is shown that the generally used Hagena scaling can result in a significant deviation from the observed data and the behaviour cannot be described by a single material condensation parameter. The results along with the nanoplasma model applied to the data of previous high harmonic generation experiments allow the independent measurement of cluster size and cluster density.

  • 6. Alonso-Mori, R.
    et al.
    Asa, K.
    Bergmann, U.
    Brewster, A. S.
    Chatterjee, R.
    Cooper, J. K.
    Frei, H. M.
    Fuller, F. D.
    Goggins, E.
    Gul, S.
    Fukuzawa, H.
    Iablonskyi, D.
    Ibrahim, M.
    Katayama, T.
    Kroll, T.
    Kumagai, Y.
    McClure, B. A.
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Motomura, K.
    Nagaya, K.
    Nishiyama, T.
    Saracini, C.
    Sato, Y.
    Sauter, N. K.
    Sokaras, D.
    Takanashi, T.
    Togashi, T.
    Ueda, K.
    Weare, W. W.
    Weng, T-C
    Yabashi, M.
    Yachandra, V. K.
    Young, I. D.
    Zouni, A.
    Kern, J. F.
    Yano, J.
    Towards characterization of photo-excited electron transfer and catalysis in natural and artificial systems using XFELs2016Ingår i: Faraday discussions, ISSN 1359-6640, E-ISSN 1364-5498, Vol. 194, s. 621-638Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ultra-bright femtosecond X-ray pulses provided by X-ray Free Electron Lasers (XFELs) open capabilities for studying the structure and dynamics of a wide variety of biological and inorganic systems beyond what is possible at synchrotron sources. Although the structure and chemistry at the catalytic sites have been studied intensively in both biological and inorganic systems, a full understanding of the atomic-scale chemistry requires new approaches beyond the steady state X-ray crystallography and X-ray spectroscopy at cryogenic temperatures. Following the dynamic changes in the geometric and electronic structure at ambient conditions, while overcoming X-ray damage to the redox active catalytic center, is key for deriving reaction mechanisms. Such studies become possible by using the intense and ultra-short femtosecond X-ray pulses from an XFEL, where sample is probed before it is damaged. We have developed methodology for simultaneously collecting X-ray diffraction data and X-ray emission spectra, using an energy dispersive spectrometer, at ambient conditions, and used this approach to study the room temperature structure and intermediate states of the photosynthetic water oxidizing metallo-protein, photosystem II. Moreover, we have also used this setup to simultaneously collect the X-ray emission spectra from multiple metals to follow the ultrafast dynamics of light-induced charge transfer between multiple metal sites. A Mn-Ti containing system was studied at an XFEL to demonstrate the efficacy and potential of this method.

  • 7. Amotchkina, Tatiana
    et al.
    Trubetskov, Michael K.
    Pervak, Yurij
    Veisz, Laszlo
    Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Pervak, Vladimir
    Stress compensation with antireflection coatings for ultrafast laser applications: from theory to practice2014Ingår i: Optics Express, E-ISSN 1094-4087, Vol. 22, nr 24, s. 30387-30393Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Each complicated coating, in particular, a dispersive mirror consists of dozens of layers. Thin films layers have mechanical stresses. After summing up stresses from all layers, the resulting stress is high enough to bend even a relatively thick substrate. To avoid this effect we suggest depositing an antireflection coating (AR) at the back-side of the substrate which together with suppression of unwanted reflections from the back side will also compensate this stress. We demonstrate unique, extremely thick and sophisticated AR coating consisting of 71 layers with the total physical thickness of 7.5 µm. This AR coating completely compensates stress from the dispersive mirror coated on the front side and minimizes unwanted reflections.

  • 8.
    Anderson, D.
    et al.
    Dept. of Electromagnetics, Chalmers University of Technology, Gothenburg, Sweden.
    Lisak, M.
    Dept. of Electromagnetics, Chalmers University of Technology, Gothenburg, Sweden.
    Marklund, M.
    Dept. of Electromagnetics, Chalmers University of Technology, Gothenburg, Sweden.
    Johannisson, P.
    Dept. of Electromagnetics, Chalmers University of Technology, Gothenburg, Sweden.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stenflo, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Collapse of optical vacuum pulses due to QED nonlinearities2002Ingår i: Nonlinear Guided Waves and Their Applications, 1–4 September 2002, Stresa, Italy, Optics Info Base, Optical Society of America, 2002, artikel-id NLMD27Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Due to quantum electrodynamical (QED) effects there are nonlinear corrections to Maxwell's equations in vacuum. We show that stationary two-dimensional light bullets can form, which are unstable and exhibit, the possibility of self-focusing collapse.

  • 9. Ans, Muhammad
    et al.
    Iqbal, Javed
    Ayub, Khurshid
    Ali, Ehsan
    Eliasson, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Spirobifluorene based small molecules as an alternative to traditional fullerene acceptors for organic solar cells2019Ingår i: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 94, s. 97-106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Four new three-dimensional (3D) acceptor-acceptor-donor (A-A-D) type of small molecule acceptors (Ml, M2, M3 and M4) were designed for better optoelectronic properties in organic solar cells. These molecules contain spirobifluorene as a 3D core unit, flanked with 2,1,3- benzothiadiazole (BT) units linked with the end-capped acceptor groups 2-(4-oxo-4,5-dihydrocyclopenta-b-thiophene-6-ylidene)malononitrile (M1), 2-(3-oxo-2,3-dihydro-1H-indene-1-indene-1-ylidene)malononitrile (M2), 2-(5,6-difluoro-3-oxo-2,3-dihydroindene-1-ylidene) malononitrile (M3) and 2-(5,6-dimethyl-3-oxo-2,3-dihydroindene-1-ylidene)malononitrile (M4). The optoelectronic properties of M1 -M4 were compared with the well-known reference molecule R, which has the same central BT-spirobifluorene-BT structure as Ml-M4 but is end-capped with the 2-(2-dicyanomethylene)-3-ethyl-4-oxo-thiazolidin-5-ylidenemethyl group. Among these molecules, M3 has the most appropriate frontier molecular orbital diagram for optoelectronic properties as deduced from MPW1PW91 calculations and also shows the maximum absorption peak at longest wavelength (569 nm) by TD-MPW1PW91 calculations with a polarizable continuum model for chloroform solution. These properties are due to the strong electron-withdrawing end-capped acceptor group which causes a red shift in the absorption spectrum. Computed reorganization energies indicate that the electron mobilities for M1-M4 are higher compared to that of reference R.

  • 10.
    Antalicz, Balázs
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Towards femtosecond time-resolved biophysics2019Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
  • 11.
    Appelblad, André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Development of a Temperature Controlled Cell for Surface Enhanced Raman Spectroscopy for in situ Detection of Gases2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta dokument beskriver ett examensarbete för civilingenjörsexamen i teknisk fysik vid Umeå Universitet som utförts under vårterminen 2014. I examensarbetet har en kyl-/värmecell för temperaturkontroll av substratytor för ytförstärkt ramanspektroskopi (SERS) för snabb detektion av farliga flyktiga ämnen konstruerats och testats. Arbetet utfördes vid Totalförsvarets forskningsinstitut (FOI) i Umeå, Sverige. Utgångspunkten var ett Linkam Scientific Instruments TS1500 mikroskopsteg, vilket utrustades med ett Peltierelement för kylning/värmning och en termistor för temperaturövervakning. Ett styrsystem baserat på ett Arduino Uno mikrostyrenhetskort konstruerades med ett motordrivkort (H-brygga) vilket använder pulsbreddsmodulering (PWM) för att reglera spänningen till Peltierelementet utifrån en PI-regulator. Den färdiga cellen klarade att reglera temperaturen på ett SERS-substrat i ett temperaturspann på ungefär -15 till +110 °C med en temperaturstabilitet på ±0.22 °C av måltemperaturen. Cellen testades sedan på flyktiga ämnen för att visa dess funktion. Difluorometyl-2,2,2-trifluoro-1-kloroetyleter (isofluran) i gasfas, med instrumentluft som bärargas, flödades genom cellen och SERS-spektra erhölls vid olika koncentrationer och temperaturer. Vid samtliga koncentrationer visades att lägre temperatur ger ökad signalstyrka. När ytan sedan värmdes upp sjönk signalen reversibelt tillbaka till ursprungsvärdet.

    Nyckelord: temperaturkontroll, ytförstärkt ramanspektroskopi, SERS, flyktiga ämnen, Peltierelement, thermistor, PWM, H-brygga, PI(D)-regulator.

    Ladda ner fulltext (pdf)
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  • 12.
    Arnesson, Fredrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    How to run a semiconductor diode laser in a stable way2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Interferometry and holography are two well-known methods for measuring distances, positions, vibrations, index of refraction etc. In these methods a coherent light source is used to create interference between different parts of the light. Since the wavelength of the light is used as reference it is possible to achieve very good accuracy in the measurements. The need of small and cheap light sources for these applications is large and an interesting alternative would be to use ordinary semiconductor diode lasers. These are unfortunately not designed to give sufficiently good coherence. In this Master Thesis work investigations of how the coherence of semiconductor diode lasers is affected by changes in temperature, injection current and between different individuals are performed. A Michelson interferometer is used to create an interference pattern where the contrast then can be analyzed. The contrast is related to the coherence of the laser, i.e., good coherence will give high contrast. The results show that in order to drive the laser in a stable way it is better to hold the temperature constant and varying the injection current until the wanted output power is achieved instead of doing the opposite. The results also indicate that the best coherence is achieved for low temperatures (around 10

    OC) and high injection currents (around 80 mA). During these conditions a contrast of 70 % -80 % is achieved. The result of this Master Thesis work gives a hint on how to run a semiconductor diode laser in a stable way.

    Ladda ner fulltext (pdf)
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  • 13.
    Auroux, Etienne
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sandström, Andreas
    LunaLEC AB, Umeå, Sweden.
    Larsen, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. LunaLEC AB, Umeå, Sweden.
    Zäll, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Lundberg, Petter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. LunaLEC AB, Umeå, Sweden.
    Evidence and Effects of Ion Transfer at Active-Material/Electrode Interfaces in Solution-Fabricated Light-Emitting Electrochemical Cells2021Ingår i: Advanced Electronic Materials, E-ISSN 2199-160X, Vol. 7, nr 8, artikel-id 2100253Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The light-emitting electrochemical cell (LEC) allows for energy- and cost-efficient printing and coating fabrication of its entire device structure, including both electrodes and the single-layer active material. This attractive fabrication opportunity is enabled by the electrochemical action of mobile ions in the active material. However, a related and up to now overlooked issue is that such solution-fabricated LECs commonly comprise electrode/active-material interfaces that are open for transfer of the mobile ions, and it is herein demonstrated that a majority of the mobile anions in a common spray-coated active material can transfer into a spray-coated poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) positive electrode during LEC operation. Since it is well established that the mobile ion concentration in the active material has a profound influence on the LEC performance, this significant ion transfer is an important factor that should be considered in the design of low-cost LEC devices that deliver high performance.

    Ladda ner fulltext (pdf)
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  • 14.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Medicinska fakulteten, Umeå Centre for Microbial Research (UCMR).
    Andersson, Magnus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Medicinska fakulteten, Umeå Centre for Microbial Research (UCMR).
    Björnham, Oscar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Medicinska fakulteten, Umeå Centre for Microbial Research (UCMR).
    Castelain, Mickaël
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Medicinska fakulteten, Umeå Centre for Microbial Research (UCMR).
    Klinth, Jeanna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Medicinska fakulteten, Umeå Centre for Microbial Research (UCMR).
    Koutris, Efstratios
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Medicinska fakulteten, Umeå Centre for Microbial Research (UCMR).
    Schedin, Staffan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Medicinska fakulteten, Umeå Centre for Microbial Research (UCMR).
    Assessing bacterial adhesion on an individual adhesin and single pili level using optical tweezers 2011Ingår i: Bacterial adhesion: chemistry, biology and physics / [ed] D. Line and A. Goldman, Berlin: Springer Berlin/Heidelberg, 2011, s. 301-313Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Optical tweezers (OT) are a technique that, by focused laser light, can both manipulate micrometer sized objects and measure minute forces (in the pN range) in biological systems. The technique is therefore suitable for assessment of bacterial adhesion on an individual adhesin-receptor and single attachment organelle (pili) level. This chapter summarizes the use of OT for assessment of adhesion mechanisms of both non-piliated and piliated bacteria. The latter include the important helix-like pili expressed by uropathogenic Escherichia coli (UPEC), which have shown to have unique and intricate biomechanical properties. It is conjectured that the large flexibility of this type of pili allows for a redistribution of an external shear force among several pili, thereby extending the adhesion lifetime of bacteria. Systems with helix-like adhesion organelles may therefore act as dynamic biomechanical machineries, enhancing the ability of bacteria to withstand high shear forces originating from rinsing flows such as in the urinary tract. This implies that pili constitute an important virulence factor and a possible target for future anti-microbial drugs.

  • 15.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Björnham, Oscar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Castelain, Mickael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Koutris, Efstratios
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schedin, Staffan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fällman, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Andersson, Magnus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Unraveling the secrets of bacterial adhesion organelles using single-molecule force spectroscopy2010Ingår i: Single molecule spectroscopy in chemistry, physics and biology: Nobel symposium / [ed] Gräslund, Astrid, Rigler, Rudolf & Widengren, Jerker, Springer, 2010, s. 337-362Konferensbidrag (Refereegranskat)
    Abstract [en]

    Many types of bacterium express micrometer-long attachment organelles (so-called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Force-measuring optical tweezers (FMOT) have since then been used to unravel the biomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated at the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g., urine flow. It has been found that many types of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.

  • 16.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ehlers, Patrick
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Silander, Isak
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wang, Junyang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    NICE-OHMS – frequency modulation cavity-enhanced spectroscopy: principles and performance2014Ingår i: Cavity-Enhanced Spectroscopy and Sensing / [ed] Gianluca Gagliardi and Hans-Peter Loock, Berlin: Springer Berlin/Heidelberg, 2014, s. 221-251Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

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

  • 17.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ehlers, Patrick
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Foltynowicz-Matyba, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Silander, Isak
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wang, Junyang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    NICE-OHMS – Frequency modulation cavity-enhanced spectroscopy: principles and performanceManuskript (preprint) (Övrigt vetenskapligt)
  • 18.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ehlers, Patrick
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Silander, Isak
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ma, Weiguang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Noise-immune cavity-enhanced analytical atomic spectrometry — NICE-AAS: a technique for detection of elements down to zeptogram amounts2014Ingår i: Spectrochimica Acta Part B - Atomic Spectroscopy, ISSN 0584-8547, E-ISSN 1873-3565, Vol. 100, s. 211-235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is a powerful technique for detection of molecular compounds in gas phase that is based on a combination of two important concepts: frequency modulation spectroscopy (FMS) for reduction of noise, and cavity enhancement, for prolongation of the interaction length between the light and the sample. Due to its unique properties, it has demonstrated unparalleled detection sensitivity when it comes to detection of molecular constituents in the gas phase. However, despite these, it has so far not been used for detection of atoms, i.e. for elemental analysis. The present work presents an assessment of the expected performance of Doppler-broadened (Db) NICE-OHMS for analytical atomic spectrometry, then referred to as noise-immune cavity-enhanced analytical atomic spectrometry (NICE-AAS). After a description of the basic principles of Db-NICE-OHMS, the modulation and detection conditions for optimum performance are identified. Based on a previous demonstrated detection sensitivity of Db-NICE-OHMS of 5×10−12 cm−1 Hz−1∕2 (corresponding to a single-pass absorbance of 7×10−11 over 10 s), the expected limits of detection (LODs) of Hg and Na by NICE-AAS are estimated. Hg is assumed to be detected in gas phase directly while Na is considered to be atomized in a graphite furnace (GF) prior to detection. It is shown that in the absence of spectral interferences, contaminated sample compartments, and optical saturation, it should be feasible to detect Hg down to 10 zg/cm3 (10 fg/m3 or 10-5 ng/m3), which corresponds to 25 atoms/cm3, and Na down to 0.5 zg (zg = zeptogram = 10-21 g), representing 50 zg/mL (parts-per-sextillion, pps, 1:1021) in liquid solution (assuming a sample of 10 µL) or solely 15 atoms injected into the GF, respectively. These LODs are several orders of magnitude lower (better) than any previous laser-based absorption technique previously has demonstrated under atmospheric pressure conditions. It is prophesied that NICE-AAS could provide such high detection sensitivity that the instrumentation should not, by itself, be the limiting factor of an assessment of elemental abundance; the accuracy of an assessment would then instead be limited by concomitant species, e.g. originating from the handling procedures of the sample or the environment.

  • 19.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Forssén, Clayton
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Silander, Isak
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zakrisson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zelan, Martin
    Ability of gas modulation to reduce the pickup of drifts in refractometry2021Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 38, nr 8, s. 2419-2436Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Gas modulation refractometry (GAMOR) is a methodology for assessment of gas refractivity, molar density, and pressure that, by a rapid gas modulation, exhibits a reduced susceptibility to various types of disturbances. Although previously demonstrated experimentally, no detailed analysis of its ability to reduce the pickup of drifts has yet been given. This work provides an explication of to what extent modulated refractometry in general, and GAMOR in particular, can reduce drifts, predominantly those of the cavity lengths, gas leakages, and outgassing. It is indicated that the methodology is insensitive to the linear parts of so-called campaign-persistent drifts and that it has a significantly reduced susceptibility to others. This makes the methodology suitable for high-accuracy assessments and out-of-laboratory applications.

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  • 20.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Ma, Weiguang
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sub-Doppler dispersion and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy revised2008Ingår i: Journal of the Optical Society of America B, Vol. 25, nr 7, s. 1166-1177Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An expression for the peak-to-peak sub-Doppler optical phase shift of two counter-propagating modes of light, to which the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) dispersion signal is proportional, valid for arbitrary degree of saturation, is derived.

    For low degrees of saturation it agrees with the expression for weakly saturating (ws) conditions, [(1+S)-1/2-(1+2S)-1/20/2, where S is the degree of saturation and α0 the unsaturated peak absorption.

    However, the new expression, which can be written as 0.45S(1+S)-1α0/2, does not predict a distinct maximum as the ws-expression does; instead it predicts an optical phase shift that increases monotonically with S and levels off to 0.45α0/2 for large S. This alters the optimum conditions for the sub-Doppler NICE-OHMS technique and improves its shot-noise-limited detectability.

    The new expression is based upon the same explicit assumptions as the ws-expression but not the Kramers-Kronig’s relations, which are not valid for nonlinear responses, and is supported by experimental results up to S = 100. The new expression is expected to be valid for all techniques measuring sub-Doppler dispersion signals

  • 21.
    Axner, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Silander, Isak
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Forssén, Clayton
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zakrisson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zelan, Martin
    Ability of gas modulation to reduce the pickup of fluctuations in refractometry2020Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 37, nr 7, s. 1956-1965Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Gas modulation refractometry is a technique for assessment of gas refractivity, density, and pressure that, by a rapid modulation of the gas, provides a means to significantly reduce the pickup of fluctuations. Although its unique feature has previously been demonstrated, no detailed explication or analysis of this ability has yet been given. This work provides a theoretical explanation, in terms of the length of the modulation cycle, of the extent to which gas modulation can reduce the pickup of fluctuations. It is indicated that a rapid modulation can significantly reduce the influence of fluctuations with Fourier frequencies lower than the inverse of the modulation cycle length, which often are those that dominate. The predictions are confirmed experimentally.

  • 22.
    Bai, Yu
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Assessment of the Emission Spectrum from a White Super-Luminescent Diode by the Use of a Fourier Transform Spectrometer2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this experiment, we use a Fourier transform spectrometer to measure the emission spectrum of a white superluminescent diode. The spectrometer is based on a Michelson interferometer with a super luminescent diode as a light source and a stepper-motordriven mirror that reflects light on both sides. Another interferometer, with a HeNe laser as a light source, sharing the movable mirror is used for a calibration of the frequency scale. When characterized with a green HeNe laser, the spectrometer shows a spectral resolution of 0.4 nm. In our experiments, we found that the superluminescent diode emits in the blue and yellow parts of the spectrum, and that the emission bandwidths are 18.1(4) nm and 143.1(4) nm respectively.

  • 23. Banerjee, S.
    et al.
    Rondoni, L.
    Mukhopadhyay, S.
    Misra, Amar P
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption2011Ingår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 284, nr 9, s. 2278-2291Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optical chaos is a topic of current research characterized by high-dimensional nonlinearity which is attributed to the delay-induced dynamics, high bandwidth and easy modular implementation of optical feedback. In light of these facts, which add enough confusion and diffusion properties for secure communications, we explore the synchronization phenomena in spatiotemporal semiconductor laser systems. The novel system is used in a two-phase colored image encryption process. The high-dimensional chaotic attractor generated by the system produces a completely randomized chaotic time series, which is ideal in the secure encoding of messages. The scheme thus illustrated is a two-phase encryption method, which provides sufficiently high confusion and diffusion properties of chaotic cryptosystem employed with unique data sets of processed chaotic sequences. In this novel method of cryptography, the chaotic phase masks are represented as images using the chaotic sequences as the elements of the image. The scheme drastically permutes the positions of the picture elements. The next additional layer of security further alters the statistical information of the original image to a great extent along the three-color planes. The intermediate results during encryption demonstrate the infeasibility for an unauthorized user to decipher the cipher image. Exhaustive statistical tests conducted validate that the scheme is robust against noise and resistant to common attacks due to the double shield of encryption and the infinite dimensionality of the relevant system of partial differential equations.

  • 24.
    Bao, Heng
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Construction of a free-space coherent laser radar for measurement of distances and velocities2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    A free space frequency modulated continuous wave (FMCW) laser radar has been realized to measure distances and velocities. The radar is based on the Michelson interferometer and the laser frequency is modulated by a 500 Hz triangular wave. From a photo detector, a beat signal of light interference can be detected. By analyzing the spectrum of the collected signal, we can calculate the distance and velocity of the target. The accuracy of distance measurement is 2.2 mm, and the velocity measurement accuracy is 0.3 mm/s. The precision of distance measurement and velocity measurement evaluated by Allan deviation are 0.39 mm and 0.365 mm/s.

  • 25. Bashinov, A. V.
    et al.
    Gonoskov, A. A.
    Kim, A. V.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mourou, G.
    Sergeev, A. M.
    Electron acceleration and emission in a field of a plane and converging dipole wave of relativistic amplitudes with the radiation reaction force taken into account2013Ingår i: Quantum electronics (Woodbury, N.Y.), ISSN 1063-7818, E-ISSN 1468-4799, Vol. 43, nr 4, s. 291-299Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A comparative analysis is performed of the electron emission characteristics as the electrons move in laser fields with ultra-relativistic intensity and different configurations corresponding to a plane or tightly focused wave. For a plane travelling wave, analytical expressions are derived for the emission characteristics, and it is shown that the angular distribution of the radiation intensity changes qualitatively even when the wave intensity is much less than that in the case of the radiation-dominated regime. An important conclusion is drawn that the electrons in a travelling wave tend to synchronised motion under the radiation reaction force. The characteristic features of the motion of electrons are found in a converging dipole wave, associated with the curvature of the phase front and nonuniformity of the field distribution. The values of the maximum achievable longitudinal momenta of electrons accelerated to the centre, as well as their distribution function are determined. The existence of quasi-periodic trajectories near the focal region of the dipole wave is shown, and the characteristics of the emission of both accelerated and oscillating electrons are analysed.

  • 26. Ben Nasr, F.
    et al.
    Matoussi, A.
    Salh, Roushdey
    Physics department, University of Rostock, Universitatsplatz 3, D‐1805 Rostock, Germany .
    Boufaden, T.
    Guermazi, S.
    Fitting, H.-J.
    Eljani, B.
    Fakhfakh, Z.
    Theoretical and Experiment Study of Cathodoluminescence of  GaN films2007Ingår i: FUNDAMENTAL AND APPLIED SPECTROSCOPY: Second International Spectroscopy Conference, ISC 2007, American Institute of Physics (AIP), 2007, Vol. 25-28, s. 65-71Konferensbidrag (Refereegranskat)
  • 27. Ben Nasr, Férid
    et al.
    Matoussi, Adel
    Salh, Roushdey
    Institute of Physics, Johannes Gutenberg University of Mainz, Staudingerweg 7, 55099 Mainz, Germany.
    Guermazi, Samir
    Fitting, H.-J.
    Cathodoluminescence study of undoped GaN films: Experimental and Calculation2009Ingår i: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 41, s. 454-459Artikel i tidskrift (Refereegranskat)
  • 28. Bergues, B.
    et al.
    Rivas, D. E.
    Weidman, M.
    Muschet, Alexander
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Helml, W.
    Guggenmos, A.
    Pervak, V.
    Kleineberg, U.
    Marcus, G.
    Kienberger, R.
    Charalambidis, D.
    Tzallas, P.
    Schröder, H.
    Krausz, F.
    Veisz, Laszlo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Tabletop nonlinear optics in the 100-eV spectral region2018Ingår i: Optica, ISSN 2334-2536, Vol. 5, nr 3, s. 237-242Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonlinear light-matter interactions in the extreme ultraviolet (XUV) are a prerequisite to perform XUV-pump/XUV-probe spectroscopy of core electrons. Such interactions are now routinely investigated at free-electron laser (FEL) facilities. Yet, electron dynamics are often too fast to be captured with the femtosecond resolution of state-of-the-art FELs. Attosecond pulses from laser-driven XUV-sources offer the necessary temporal resolution. However, intense attosecond pulses supporting nonlinear processes have only been available for photon energy below 50 eV, precluding XUV-pump/XUV-probe investigation of typical inner-shell processes. Here, we surpass this limitation by demonstrating two-photon absorption from inner electronic shells of xenon at photon energies around 93 eV and 115 eV. This advance opens the door for attosecond real-time observation of nonlinear electron dynamics deep inside atoms.

  • 29. Bergues, B.
    et al.
    Rivas, D. E.
    Weidman, M.
    Muschet, Alexander
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, 85748, Garching, Germany.
    Helml, W.
    Guggenmos, A.
    Pervak, V.
    Matyba, Piotr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kleineberg, U.
    Marcus, G.
    Kienberger, R.
    Charalambidis, D.
    Tzallas, P.
    Schröder, H.
    Krausz, F.
    Veisz, Laszlo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Towards Attosecond XUV-Pump XUV-Probe Measurements in the 100-eV Region2017Ingår i: 2017 Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), IEEE, 2017Konferensbidrag (Refereegranskat)
  • 30.
    Bergues, B.
    et al.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; Physics Department, Ludwig-Maximilians-Universität München, Am Couloumbwall 1, Garching, Germany.
    Rivas, D.E.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; Physics Department, Ludwig-Maximilians-Universität München, Am Couloumbwall 1, Garching, Germany.
    Weidman, M.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany.
    Muschet, Alexander
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany.
    Helml, W.
    Physics Department, Technische Universität München, James-Frank-Str. 1, Garching, Germany.
    Guggenmos, A.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; Physics Department, Ludwig-Maximilians-Universität München, Am Couloumbwall 1, Garching, Germany.
    Pervak, V.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; Physics Department, Ludwig-Maximilians-Universität München, Am Couloumbwall 1, Garching, Germany.
    Kleineberg, U.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; Physics Department, Ludwig-Maximilians-Universität München, Am Couloumbwall 1, Garching, Germany.
    Marcus, G.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; The Hebrew University of Jerusalem, Jerusalem, Israel.
    Kienberger, R.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; Physics Department, Technische Universität München, James-Frank-Str. 1, Garching, Germany.
    Charalambidis, D.
    Foundation for Research and Technology-Hellas, Institute of Electronic Structure and Laser, PO Box 1527, Heraklion, Crete, Greece.
    Tzallas, P.
    Foundation for Research and Technology-Hellas, Institute of Electronic Structure and Laser, PO Box 1527, Heraklion, Crete, Greece.
    Schröder, H.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany.
    Krausz, F.
    Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany; Physics Department, Ludwig-Maximilians-Universität München, Am Couloumbwall 1, Garching, Germany.
    Veisz, Laszlo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, Garching, Germany.
    Nonlinear interaction of 100-eV attosecond XUV-pulses with core electrons in Xenon2018Ingår i: Optics InfoBase Conference Papers, Optica Publishing Group , 2018, artikel-id HM2A.6Konferensbidrag (Refereegranskat)
    Abstract [en]

    We demonstrate multiphoton ionization of inner-shell electrons in Xenon with 100-eV attosecond pulses. This was achieved with a novel XUV source based on high-harmonic generation in the gas phase driven with multi-TW few-cycle laser pulses.

  • 31. Björklund Svensson, Jonas
    et al.
    Guénot, Diego
    Ferri, Julien
    Ekerfelt, Henrik
    Gallardo González, Isabel
    Persson, Anders
    Svendsen, Kristoffer
    Veisz, Laszlo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Lundh, Olle
    Low-divergence femtosecond X-ray pulses from a passive plasma lens2021Ingår i: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 17, nr 5, s. 639-645Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electron and X-ray beams originating from compact laser-wakefield accelerators have very small source sizes that are typically on the micrometre scale. Therefore, the beam divergences are relatively high, which makes it difficult to preserve their high quality during transport to applications. To improve on this, tremendous efforts have been invested in controlling the divergence of the electron beams, but no mechanism for generating collimated X-ray beams has yet been demonstrated experimentally. Here we propose and realize a scheme where electron bunches undergoing focusing in a dense, passive plasma lens can emit X-ray pulses with divergences approaching the incoherent limit. Compared with conventional betatron emission, the divergence of this so-called plasma lens radiation is reduced by more than an order of magnitude in solid angle, while maintaining a similar number of emitted photons per electron. This X-ray source offers the possibility of producing brilliant and collimated few-femtosecond X-ray pulses for ultra-fast science, in particular for studies based on X-ray diffraction and absorption spectroscopy.Main

  • 32.
    Blagojevic, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Weather effects on short-range LiDAR and their classification2022Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Today we are seeing exciting developments in the field of autonomous vehicles, on both software and hardware. Veoneer is a company making a contribution where research and manufacturing is being done on hardware and active safety. One of the most important aspects in this field is road safety, where understanding the behaviour of sensors used in vehicles is essential. From the point of view of safety, understanding how weather affects the sensors is necessary for a successful deployment. This study is a continuation of previous studies done at Veoneer, and regards how various adverse condition affect the performance of a short-range LiDAR and gives a thorough description of the involved physical processes. Data collected over a couple of months was analysed and compared to theoretical models in order to establish their validity. In addition, LiDAR measurement were done in a chamber where conditions could be varied in a controlled manner. Furthermore, analysis methods were used to transform the data into a form potentially more useful for use in machine learning algorithms to estimate the ability to classify conditions based on LiDAR signals. The used models showed mixed results, with some showing more agreement than others. Models regarding foggy conditions generally showed greater agreement with data than in other conditions, although some variation around the predictions did occur. In regards to the performance of the classification algorithms, there were als omixed results, where the sensitivity in fog was at most 96 % and the precision at most 64 %. This thesis also enables and suggests further research into the utility of short-range LiDAR both in the field of autonomous vehicle safety as well as in use of other fields such as meteorology.

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  • 33. Boudreau, Denis
    et al.
    Ljungberg, Peter
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    DensMat: fully time-resolved simulation of two-step pulsed laser excitation of atoms in highly collisional media1996Ingår i: Spectrochimica Acta Part B - Atomic Spectroscopy, ISSN 0584-8547, E-ISSN 1873-3565, Vol. 51, nr 4, s. 413-428Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A program that simulates and displays the level populations of atomic systems exposed to dual-wavelength (i.e. two-colour) pulsed laser excitation in highly collisional media (such as flames and plasmas) has been developed. The program is based upon a previously published fully time-dependent density-matrix model that describes step-wise excitations of atoms with degenerate states under collision-dominated conditions, and which thus goes beyond the rate-equations formalism. This model can predict such phenomena as Rabi flopping and a.c.-Stark splitting, shifting and broadening. The program can be used as a prediction tool for laser-enhanced ionization, laser-induced fluorescence, fluorescence dip spectroscopy and other two-colour laser-based spectroscopic experiments. The program provides the user with a flexible four-level atomic system, configurable as a one- or two-step excitation ladder, along with an ionization continuum and non-laser-connected level(s) that may act as trap(s) or metastable level(s). Parameters such as level degeneracy, collisional rates and laser pulse widths, shapes, wavelengths, intensities and bandwidths are accessible to the user. The program can display both the time development of the level populations and also level populations versus laser wavelength. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a disk containing the program DensMat, an associated on-line help file and manual, an installation program, and data files pertaining to the examples illustrated in this article. The program runs under Windows 3.1 on an IBM-compatible computer.

  • 34.
    Brodin, Gert
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Servin, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Photon frequency conversion induced by gravitational radiation2001Ingår i: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 63, artikel-id 124003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the propagation of gravitational radiation in a magnetized multicomponent plasma. It is shown that large density perturbations can be generated, even for small deviations from flat space, provided the cyclotron frequency is much larger than the plasma frequency. Furthermore, the induced density gradients can generate frequency conversion of electromagnetic radiation, which may give rise to an indirect observational effect of the gravitational wave

  • 35. Brüning, E
    et al.
    Mäkelä, Harri
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Messina, A
    Petruccione, F
    Parametrizations of density matrices2012Ingår i: Journal of Modern Optics, ISSN 0950-0340, E-ISSN 1362-3044, Vol. 59, nr 1, s. 1-20Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    This article gives a brief overview of some recent progress in the characterization and parametrization of density matrices of finite dimensional systems. We discuss in some detail the Bloch-vector and Jarlskog parametrizations and mention briefly the coset parametrization. As applications of the Bloch parametrization we discuss the trace invariants for the case of time dependent Hamiltonians and in some detail the dynamics of three-level systems. Furthermore, the Bloch vector of two-qubit systems as well as the use of the polarization operator basis is indicated. As the main application of the Jarlskog parametrization we construct density matrices for composite systems. In addition, some recent related articles are mentioned without further discussion.

  • 36. Buck, A.
    et al.
    Wenz, J.
    Xu, Jiancai
    Khrennikov, K.
    Schmid, K.
    Heigoldt, M.
    Mikhailova, J. M.
    Geissler, M.
    Shen, B.
    Krausz, F.
    Karsch, S.
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Shock-Front Injector for High-Quality Laser-Plasma Acceleration2013Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, nr 18, artikel-id 185006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the generation of stable and tunable electron bunches with very low absolute energy spread (ΔE≈5  MeV) accelerated in laser wakefields via injection and trapping at a sharp downward density jump produced by a shock front in a supersonic gas flow. The peak of the highly stable and reproducible electron energy spectrum was tuned over more than 1 order of magnitude, containing a charge of 1–100 pC and a charge per energy interval of more than 10  pC/MeV. Laser-plasma electron acceleration with Ti:sapphire lasers using this novel injection mechanism provides high-quality electron bunches tailored for applications.

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    fulltext
  • 37.
    Buckland, Philip I.
    et al.
    Umeå universitet, Humanistiska fakulteten, Institutionen för idé- och samhällsstudier, Miljöarkeologiska laboratoriet.
    Hammarlund, Dan
    Lund University.
    Hjärthner-Holdar, Eva
    Swedish National Historical Museums.
    Lidén, Kerstin
    Stockholm University.
    Lindahl, Anders
    Lund University.
    Palm, Fredrik
    Umeå universitet, Humanistiska fakulteten, Humlab.
    Possnert, Göran
    Uppsala University.
    The Strategic Environmental Archaeology Database: a resource for international, multiproxy and transdisciplinary studies of environmental and climatic change2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Climate and environmental change are global challenges which require global data and infrastructure to investigate. These challenges also require a multi-proxy approach, integrating evidence from Quaternary science and archaeology with information from studies on modern ecology and physical processes among other disciplines. The Strategic Environmental Archaeology Database (SEAD http://www.sead.se) is a Swedish based international research e-infrastructure for storing, managing, analysing and disseminating palaeoenvironmental data from an almost unlimited number of analysis methods. The system currently makes available raw data from over 1500 sites (>5300 datasets) and the analysis of Quaternary fossil insects, plant macrofossils, pollen, geochemistry and sediment physical properties, dendrochronology and wood anatomy, ceramic geochemistry and bones, along with numerous dating methods. This capacity will be expanded in the near future to include isotopes, multi-spectral and archaeo-metalurgical data. SEAD also includes expandable climate and environment calibration datasets, a complete bibliography and extensive metadata and services for linking these data to other resources. All data is available as Open Access through http://qsead.sead.se and downloadable software.

     

    SEAD is maintained and managed at the Environmental Archaeology Lab and HUMlab at Umea University, Sweden. Development and data ingestion is progressing in cooperation with The Laboratory for Ceramic Research and the National Laboratory for Wood Anatomy and Dendrochronology at Lund University, Sweden, the Archaeological Research Laboratory, Stockholm University, the Geoarchaeological Laboratory, Swedish National Historical Museums Agency and several international partners and research projects. Current plans include expanding its capacity to serve as a data source for any system and integration with the Swedish National Heritage Board's information systems.

     

    SEAD is partnered with the Neotoma palaeoecology database (http://www.neotomadb.org) and a new initiative for building cyberinfrastructure for transdisciplinary research and visualization of the long-term human ecodynamics of the North Atlantic funded by the National Science Foundation (NSF).

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    Poster
  • 38.
    Cao, Yifei
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Applying digital holographic imaging to investigate microparticle diffusion using a point source2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The aim of this experiment is to measure the particle diffusion coefficient by digital holographic imaging. We first built a digital holographic microscopy (DHM) system using a laser, an objective, and a camera. Holograms of polystyrene particles with a diameter of one micron were obtained with the system. We track the particle and use reconstruction algorithm to get 3-dimensional information in X, Y, Z direction, where X-Y plane is the plane of sample table, Z is the light propagation direction. We used the particle trajectory to estimate the particle diffusion coefficient in water. The result shows the diffusion coefficient is 4.405*10-13m2s-1, 4,479*10-13m2s-1, 3.321*10-13m2s-1 for X, Y, Z direction respectively.

  • 39.
    Carcedo Martínez, Antón
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Spectroscopic characterization of iodine and assessment of excitationtransitions induced by four different HeNe lasers2022Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This experiment used a grating spectrometer to characterize the laser-induced fluorescence(LIF) emission spectrum of a molecular iodine (I2) vapor sample generated by four different helium-neon (HeNe) lasers. After the spectrometer calibration, Python based simulations were used in order to match the data to a candidate upper state that can yield the emission spectrum. To correlate the candidate state with the measurements it was assumed that the laser excites the molecules from the electronic groundstate, X1Σ+g , to the excited electronic state B3Π+0u.

    The results showed that the more intense transition series in the green HeNe LIF spectrum were yielded by the upper state J′= 109 v′= 27, in the yellow laser it was J′= 186 v′= 17, in the orange HeNe LIF spectrum J′= 50 v′= 9 was obtained and for the red laser the state J′= 130 v′= 11 was found. It was also possible to characterize weaker peak series in the orange and red spectra, where the responsible upper states were J′= 45 v′= 11 and J′= 30 v′= 6 respectively. For each of the analyzed spectra the most intense emission line was identified as R(110)27-0 in the green HeNe LIF spectrum, R(187)17-2 in the spectrum yielded by the emissions of the yellow laser, P(49)9-2 in the orange HeNe LIF spectrum and R(131)11-5 in the spectrum induced by the red laser.

    The conclusion is that regarding the case of the red and green LIF spectroscopy the data are sufficient to be used to calibrate the wavelength scales of spectrometers. The results from the orange and yellow emission spectrum were concluded not accurate enough in order to be used in calibrations. Moreover, the use of machine learning algorithms is proposed to improve the matching of the emission spectrum to the upper state that yields the transition series. The implementation of machine learning aims to increase the accuracy and reliability of the results and automatizing the data analysis.

  • 40. Cardenas, D. E.
    et al.
    Ostermayr, T. M.
    Di Lucchio, L.
    Hofmann, L.
    Kling, M. F.
    Gibbon, P.
    Schreiber, J.
    Veisz, Laszlo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Sub-cycle dynamics in relativistic nanoplasma acceleration2019Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 9, artikel-id 7321Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction of light with nanometer-sized solids provides the means of focusing optical radiation to sub-wavelength spatial scales with associated electric field enhancements offering new opportunities for multifaceted applications. We utilize collective effects in nanoplasmas with sub-two-cycle light pulses of extreme intensity to extend the waveform-dependent electron acceleration regime into the relativistic realm, by using 106 times higher intensity than previous works to date. Through irradiation of nanometric tungsten needles, we obtain multi-MeV energy electron bunches, whose energy and direction can be steered by the combined effect of the induced near-field and the laser field. We identified a two-step mechanism for the electron acceleration: (i) ejection within a sub-half-optical-cycle into the near-field from the target at >TVm−1 acceleration fields, and (ii) subsequent acceleration in vacuum by the intense laser field. Our observations raise the prospect of isolating and controlling relativistic attosecond electron bunches, and pave the way for next generation electron and photon sources.

    Ladda ner fulltext (pdf)
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    supplementary information
  • 41.
    Cardenas, Daniel
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Garching, Germany; Ludwig-Maximilian-Universität München, Am Coulombwall 1, 85748, Garching, Germany.
    Chou, Shao-Wei
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Garching, Germany; Ludwig-Maximilian-Universität München, Am Coulombwall 1, 85748, Garching, Germany; Center for High Energy and High Field Physics, National Central University, Chungli 32001, Taiwan .
    Wallin, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Xu, J.
    Buck, A.
    Schmid, K.
    Rivas, D.E.
    Shen, B.
    Gonoskov, A.
    Marklund, M.
    Veisz, Laszlo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Electron bunch evolution in laser-wakefield acceleration2020Ingår i: Physical Review Accelerators and Beams, E-ISSN 2469-9888, Vol. 23, artikel-id 112803Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on systematic and high-precision measurements of the evolution of electron beams in a laser-wakefield accelerator (LWFA). Utilizing shock-front injection, a technique providing stable, tunable and high-quality electron bunches, acceleration and deceleration of few-MeV quasimonoenergetic beams were measured with cutting-edge technology sub-5-fs and 8-fs laser pulses. We explain the observations with dephasing, an effect that fundamentally limits the performance of LWFAs. Typical density dependent electron energy evolution with 57–300  μm dephasing length and 6–20 MeV peak energy was observed and is well described by a parabolic fit. This is a promising electron source for time-resolved few-fs electron diffraction.

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    fulltext
  • 42. Centeno, R.
    et al.
    Mandon, J.
    Cristescu, S. M.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Harren, F. J. M.
    External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation2015Ingår i: Optics Express, E-ISSN 1094-4087, Vol. 23, nr 5, s. 6277-6282Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We combine an external cavity diode laser with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using current modulation. With a finesse of 1600, we demonstrate noise equivalent absorption sensitivities of 4.1 x 10(-10) cm(-1) Hz(-1/2), resulting in sub-ppbv detection limits for Doppler-broadened transitions of CH4 at 6132.3 cm(-1), C2H2 at 6578.5 cm(-1) and HCN at 6541.7 cm(-1). The system is used for hydrogen cyanide detection from sweet almonds.

  • 43. Cetoli, Alberto
    et al.
    Lundh, Emil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Loss of coherence and superfluid depletion in an optical quasicrystal2013Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, nr 8, s. 085302-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study numerically a 2D Bose-Einstein condensate in a quasiperiodic array of potential peaks, assumed to be generated by superimposing five blue detuned laser beams. By using a Bogoliubov ansatz we show that the system experiences a loss of coherence and starts developing a normal part. We give estimates where a phase transition to an insulating phase should happen for the use of future experiments, along with a study of the validity of the Bogoliubov approximation.

  • 44. Chatterjee, Ruchira
    et al.
    Weninger, Clemens
    Loukianov, Anton
    Gul, Sheraz
    Fuller, Franklin D.
    Cheah, Mun Hon
    Fransson, Thomas
    Pham, Cindy C.
    Nelson, Silke
    Song, Sanghoon
    Britz, Alexander
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Department of Chemistry, Ångström Laboratory, Molecular Biomimetics, Uppsala University, Sweden.
    Bergmann, Uwe
    Alonso-Mori, Roberto
    Yachandra, Vittal K.
    Kern, Jan
    Yano, Junko
    XANES and EXAFS of dilute solutions of transition metals at XFELs2019Ingår i: Journal of Synchrotron Radiation, ISSN 0909-0495, E-ISSN 1600-5775, Vol. 26, s. 1716-1724Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work has demonstrated that X-ray absorption spectroscopy (XAS), both Mn XANES and EXAFS, of solutions with millimolar concentrations of metal is possible using the femtosecond X-ray pulses from XFELs. Mn XAS data were collected using two different sample delivery methods, a Rayleigh jet and a drop-on-demand setup, with varying concentrations of Mn. Here, a new method for normalization of XAS spectra based on solvent scattering that is compatible with data collection from a highly variable pulsed source is described. The measured XANES and EXAFS spectra of such dilute solution samples are in good agreement with data collected at synchrotron sources using traditional scanning protocols. The procedures described here will enable XFEL-based XAS on dilute biological samples, especially metalloproteins, with low sample consumption. Details of the experimental setup and data analysis methods used in this XANES and EXAFS study are presented. This method will also benefit XAS performed at high-repetition-rate XFELs such as the European XFEL, LCLS-II and LCLS-II-HE.

  • 45.
    Chekalin, Nikolai
    et al.
    V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow, Russia.
    Marunkov, Alexander
    V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow, Russia.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Chalmers University of Technology, Gothenburg, Sweden.
    Laser-induced fluorescence in graphite furnaces under low pressure conditions as a powerful technique for studies of atomization mechanisms: investigation of Ag1994Ingår i: Spectrochimica Acta Part B - Atomic Spectroscopy, ISSN 0584-8547, E-ISSN 1873-3565, Vol. 49, nr 12-14, s. 1411-1435Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new method for accurate studies of atomization processes of various elements in graphite furnaces has been developed. It utilizes the highly sensitive Laser-Induced Fluorescence spectrometry technique for detection of atoms in Graphite Furnaces under Low Pressure conditions (LIF-GF-LP). The high sensitivity of the LIF technique enables the study of atomization processes at low pressures under true analytical conditions (i.e. for low analyte mass) with a minimum of influences from diffusion processes. This first work is concerned with an investigation of the atomization mechanisms of Ag. It was found that the LIF-GF signal area was linear with pressure for virtually all pressures. The LIF-GF signal shape (versus time as well as versus 1/T) was found to vary with both pressure and concentration. The signals were, in general, found to have a shorter duration and higher appearance and peak temperatures, the higher the pressure. Activation energies could be evaluated from the LIF-GF-LP curves very accurately by the Smets method. Excellent agreements with the predicted linear relationship were obtained for a major part of the signal curve (> 50%) under many sample and furnace conditions. Studies of the activation energy dependence on pressure, analyte mass and heating rate gave valuable information about the atomization mechanisms of Ag in graphite furnaces. The findings support a picture that Ag atomizes as individual adatoms under low pressure and low analyte mass conditions. Under atmospheric conditions, repeated desorption and adsorption processes delay the appearance of the signal in time as well as being responsible for formation of 2-D and 3-D microstructures on the surface.

  • 46.
    Chen, Chunlin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Construction of a fiber-coupled coherent laser radar for measurement of distances and velocities2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The purpose of this experiment is to measure the distance and velocity of the translation stage using a Laser radar (LIDAR). The formula with regression coefficients derived from a calibration set, is used to calculate distances. In addition, we use Allan variance to calculate the stability of frequency. As for the result, the best resolution of distance can reach 0.047 mm and velocity resolution is 0.001 mm/s. The most stable time appears when frequency modulation works continuously for about 5.8 seconds.

  • 47. Chen, Cong
    et al.
    Tao, Zhensheng
    Carr, Adra
    Matyba, Piotr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. JILA, Department of Physics, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309, United States.
    Szilvasi, Tibor
    Emmerich, Sebastian
    Piecuch, Martin
    Keller, Mark
    Zusin, Dmitriy
    Eich, Steffen
    Rollinger, Markus
    Youa, Wenjing
    Mathias, Stefan
    Thumm, Uwe
    Mavrikakis, Manos
    Aeschlimann, Martin
    Oppeneer, Peter M.
    Kapteyn, Henry
    Murnane, Margaret
    Distinguishing attosecond electron-electron scattering and screening in transition metals2017Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, nr 27, s. E5300-E5307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electron-electron interactions are the fastest processes in materials, occurring on femtosecond to attosecond timescales, depending on the electronic band structure of the material and the excitation energy. Such interactions can play a dominant role in light-induced processes such as nano-enhanced plasmonics and catalysis, light harvesting, or phase transitions. However, to date it has not been possible to experimentally distinguish fundamental electron interactions such as scattering and screening. Here, we use sequences of attosecond pulses to directly measure electron-electron interactions in different bands of different materials with both simple and complex Fermi surfaces. By extracting the time delays associated with photoemission we show that the lifetime of photoelectrons from the d band of Cu are longer by similar to 100 as compared with those from the same band of Ni. We attribute this to the enhanced electron-electron scattering in the unfilled d band of Ni. Using theoretical modeling, we can extract the contributions of electron-electron scattering and screening in different bands of different materials with both simple and complex Fermi surfaces. Our results also show that screening influences high-energy photoelectrons (approximate to 20 eV) significantly less than low-energy photoelectrons. As a result, high-energy photoelectrons can serve as a direct probe of spin-dependent electron-electron scattering by neglecting screening. This can then be applied to quantifying the contribution of electron interactions and screening to low-energy excitations near the Fermi level. The information derived here provides valuable and unique information for a host of quantum materials.

  • 48.
    Chen, Hui
    et al.
    Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
    Baitenov, Adil
    Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Kista, Sweden.
    Li, Yuanyuan
    Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology,Stockholm, Sweden.
    Vasileva, Elena
    Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Kista, Sweden.
    Popov, Sergei
    Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Kista, Sweden.
    Sychugov, Ilya
    Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology,, Kista, Sweden.
    Yan, Max
    Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Kista, Sweden.
    Berglund, Lars
    Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
    Thickness dependence of optical transmittance of transparent wood: chemical modification effects2019Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, nr 38, s. 35451-35457Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transparent wood (TW) is an emerging optical material combining high optical transmittance and haze for structural applications. Unlike nonscattering absorbing media, the thickness dependence of light transmittance for TW is complicated because optical losses are also related to increased photon path length from multiple scattering. In the present study, starting from photon diffusion equation, it is found that the angle-integrated total light transmittance of TW has an exponentially decaying dependence on sample thickness. The expression reveals an attenuation coefficient which depends not only on the absorption coefficient but also on the diffusion coefficient. The total transmittance and thickness were measured for a range of TW samples, from both acetylated and nonacetylated balsa wood templates, and were fitted according to the derived relationship. The fitting gives a lower attenuation coefficient for the acetylated TW compared to the nonacetylated one. The lower attenuation coefficient for the acetylated TW is attributed to its lower scattering coefficient or correspondingly lower haze. The attenuation constant resulted from our model hence can serve as a singular material parameter that facilitates cross-comparison of different sample types, at even different thicknesses, when total optical transmittance is concerned. The model was verified with two other TWs (ash and birch) and is in general applicable to other scattering media.

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  • 49.
    Chen, Hui
    et al.
    Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
    Montanari, Céline
    Wallenberg Wood Science Center;Department of Fiber and Polymer Technology;KTH Royal Institute of Technology;Stockholm;Sweden.
    Yan, Max
    Department of Applied Physics, KTH Royal Institute of Technology, Stockholm, Sweden.
    Popov, Sergei
    Department of Applied Physics, KTH Royal Institute of Technology, Stockholm, Sweden.
    Li, Yuanyuan
    Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
    Sychugov, Ilya
    Department of Applied Physics, KTH Royal Institute of Technology, Stockholm, Sweden.
    Berglund, Lars A
    Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
    Refractive index of delignified wood for transparent biocomposites2020Ingår i: RSC Advances, E-ISSN 2046-2069, Vol. 10, nr 67, s. 40719-40724Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Refractive index (RI) determination for delignified wood templates is vital for transparent wood composite fabrication. Reported RIs in the literature are based on either single plant fibers or wood powder, measured by the immersion liquid method (ILM) combined with mathematical fitting. However, wood structure complexity and the physical background of the fitting were not considered. In this work, RIs of delignified wood templates were measured by the ILM combined with a light transmission model developed from the Fresnel reflection/refraction theory for composite materials. The RIs of delignified balsa wood are 1.536 ± 0.006 and 1.525 ± 0.008 at the wavelength of 589 nm for light propagating perpendicular and parallel to the wood fiber direction, respectively. For delignified birch wood, corresponding values are 1.537 ± 0.005 and 1.529 ± 0.006, respectively. The RI data for delignified wood scaffolds are important for tailoring optical properties of transparent wood biocomposites, and also vital in optical properties investigations by theoretical modelling of complex light propagation in transparent wood and related composites. The developed light transmission model in combination with the immersion liquid method can be used to determine the RI of complex porous or layered solid materials and composites.

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    fulltext
  • 50.
    Chen, Sihong
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Realization of a fiber-based frequency modulated DFB-laser-based laser radar for measurement of distances and velocities2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This paper presents the construction and a performance study of a fiber-based frequency modulated continuous wave (FMCW) laser radar for measurement of distance and velocity. The current to a distributed feedback laser (DFB) was modulated to get the frequency modulated light used to construct the fiber based laser radar system. The Allan variance was used for evaluating the stability of the laser radar system. To optimize the system, the performance with different modulation frequencies was compared. The minimum measurable distances for 10 Hz, 50 Hz and 100 Hz modulation frequency system are 0.1, 0.1 and 0.8 cm respectively.

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