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  • 1.
    Abd Alrahman, Chadi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    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.
    Qu, Zhechao
    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.
    Cavity-enhanced optical frequency comb spectroscopy of high-temperature H2O in a flame2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 11, p. 13889-13895Article in journal (Refereed)
    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 University, Faculty of Science and Technology, Department of Physics.
    Development of breath sampling system for detection of exhaled nitric oxide by Faraday modulation spectroscopy2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    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 University, Faculty of Science and Technology, Department of Physics.
    Realization of an instrumentation for detection of acetylene in breath by the NICE-OHMS technique2014Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
    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. Aladi, M.
    et al.
    Bolla, R.
    Cardenas, D. E.
    Veisz, László
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foldes, I. B.
    Cluster size distributions in gas jets for different nozzle geometries2017In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 12, article id C06020Article in journal (Refereed)
    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.

  • 5. 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 University, Faculty of Science and Technology, Department of Chemistry.
    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 XFELs2016In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 194, p. 621-638Article in journal (Refereed)
    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.

  • 6. 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 practice2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 24, p. 30387-30393Article in journal (Refereed)
    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.

  • 7.
    Appelblad, André
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Development of a Temperature Controlled Cell for Surface Enhanced Raman Spectroscopy for in situ Detection of Gases2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This work describes a master’s thesis in engineering physics at Umeå University carried out during the spring semester of 2014. In the thesis the student has constructed and tested a temperature controlled cell for cooling/heating of surface-enhanced-Raman-spectroscopy (SERS) substrates for rapid detection of volatile substances. The thesis was carried out at the Swedish Defence Research Agency (FOI) in Umeå, Sweden. A Linkam Scientific Instruments TS1500 cell was equipped with a Peltier element for cooling/heating and a thermistor temperature sensor. A control system was constructed, based on an Arduino Uno microcontroller board and a pulse-width-modulated (PWM) H-bridge motor driver to control the Peltier element using a proportional-integral (PI) control algorithm. The temperature controlled cell was able to regulate the temperature of a SERS substrate within -15 to +110 °C and maintain the temperature over prolonged periods at ±0.22 °C of the set point temperature. Gas phase of 2-chloro-2-(difluoromethoxy)-1,1,1-trifluoro-ethane (isoflurane) was flowed through the cell and SERS spectra were collected at different temperatures and concentrations. This test showed that the signal is increased when the substrate is cooled and reversibly decreased when the substrate was heated.

    Keywords: temperature control, Raman scattering, surface enhanced Raman spectroscopy SERS, SERS substrate, volatile substances, Peltier module, thermistor, PWM, H-bridge, PI(D) control.

  • 8.
    Arnesson, Fredrik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    How to run a semiconductor diode laser in a stable way2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    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.

  • 9.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Björnham, Oscar
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Castelain, Mickaël
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Klinth, Jeanna
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Koutris, Efstratios
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Assessing bacterial adhesion on an individual adhesin and single pili level using optical tweezers 2011In: Bacterial adhesion: chemistry, biology and physics / [ed] D. Line and A. Goldman, Berlin: Springer Berlin/Heidelberg, 2011, p. 301-313Chapter in book (Refereed)
    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.

  • 10.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Björnham, Oscar
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Castelain, Mickael
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Koutris, Efstratios
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Unraveling the secrets of bacterial adhesion organelles using single-molecule force spectroscopy2010In: Single molecule spectroscopy in chemistry, physics and biology: Nobel symposium / [ed] Gräslund, Astrid, Rigler, Rudolf & Widengren, Jerker, Springer, 2010, p. 337-362Conference paper (Refereed)
    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.

  • 11.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    NICE-OHMS – frequency modulation cavity-enhanced spectroscopy: principles and performance2014In: Cavity-Enhanced Spectroscopy and Sensing / [ed] Gianluca Gagliardi and Hans-Peter Loock, Berlin: Springer Berlin/Heidelberg, 2014, p. 221-251Chapter in book (Refereed)
    Abstract [en]

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

  • 12.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz-Matyba, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    NICE-OHMS – Frequency modulation cavity-enhanced spectroscopy: principles and performanceManuscript (preprint) (Other academic)
  • 13.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Noise-immune cavity-enhanced analytical atomic spectrometry — NICE-AAS: a technique for detection of elements down to zeptogram amounts2014In: Spectrochimica Acta Part B - Atomic Spectroscopy, ISSN 0584-8547, E-ISSN 1873-3565, Vol. 100, p. 211-235Article in journal (Refereed)
    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.

  • 14.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Physics. Umeå University, Faculty of Science and Technology, Physics.
    Sub-Doppler dispersion and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy revised2008In: Journal of the Optical Society of America B, Vol. 25, no 7, p. 1166-1177Article in journal (Refereed)
    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

  • 15.
    Bai, Yu
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of the Emission Spectrum from a White Super-Luminescent Diode by the Use of a Fourier Transform Spectrometer2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this experiment, we use a Fourier transform spectrometer to measure the 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.

  • 16. Banerjee, S.
    et al.
    Rondoni, L.
    Mukhopadhyay, S.
    Misra, Amar P
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption2011In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 284, no 9, p. 2278-2291Article in journal (Refereed)
    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.

  • 17.
    Bao, Heng
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a free-space coherent laser radar for measurement of distances and velocities2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    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.

  • 18. Bashinov, A. V.
    et al.
    Gonoskov, A. A.
    Kim, A. V.
    Marklund, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    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 account2013In: Quantum electronics (Woodbury, N.Y.), ISSN 1063-7818, E-ISSN 1468-4799, Vol. 43, no 4, p. 291-299Article in journal (Refereed)
    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.

  • 19. 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 films2007In: FUNDAMENTAL AND APPLIED SPECTROSCOPY: Second International Spectroscopy Conference, ISC 2007, American Institute of Physics (AIP), 2007, Vol. 25-28, p. 65-71Conference paper (Refereed)
  • 20. 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 Calculation2009In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 41, p. 454-459Article in journal (Refereed)
  • 21. Bergues, B.
    et al.
    Rivas, D. E.
    Weidman, M.
    Muschet, A. A.
    Umeå University, Faculty of Science and Technology, Department of Physics. 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, L.
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Tabletop nonlinear optics in the 100-eV spectral region2018In: Optica, ISSN 2334-2536, Vol. 5, no 3, p. 237-242Article in journal (Refereed)
    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.

  • 22. Brüning, E
    et al.
    Mäkelä, Harri
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Messina, A
    Petruccione, F
    Parametrizations of density matrices2012In: Journal of Modern Optics, ISSN 0950-0340, E-ISSN 1362-3044, Vol. 59, no 1, p. 1-20Article, review/survey (Refereed)
    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.

  • 23. 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 Acceleration2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 18, article id 185006Article in journal (Refereed)
    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.

  • 24.
    Buckland, Philip I.
    et al.
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab.
    Hammarlund, Dan
    Lund University.
    Hjärthner-Holdar, Eva
    Swedish National Historical Museums.
    Lidén, Kerstin
    Stockholm University.
    Lindahl, Anders
    Lund University.
    Palm, Fredrik
    Umeå University, Faculty of Arts, Humlab.
    Possnert, Göran
    Uppsala University.
    The Strategic Environmental Archaeology Database: a resource for international, multiproxy and transdisciplinary studies of environmental and climatic change2015Conference paper (Refereed)
    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).

  • 25.
    Cao, Yifei
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Applying digital holographic imaging to investigate microparticle diffusion using a point source2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    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.

  • 26. Centeno, R.
    et al.
    Mandon, J.
    Cristescu, S. M.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Harren, F. J. M.
    External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 5, p. 6277-6282Article in journal (Refereed)
    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.

  • 27. Cetoli, Alberto
    et al.
    Lundh, Emil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Loss of coherence and superfluid depletion in an optical quasicrystal2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 8, p. 085302-Article in journal (Refereed)
    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.

  • 28.
    Chen, Chunlin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a fiber-coupled coherent laser radar for measurement of distances and velocities2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    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.

  • 29. Chen, Cong
    et al.
    Tao, Zhensheng
    Carr, Adra
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics. 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 metals2017In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, no 27, p. E5300-E5307Article in journal (Refereed)
    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.

  • 30.
    Chen, Sihong
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Realization of a fiber-based frequency modulated DFB-laser-based laser radar for measurement of distances and velocities2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    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.

  • 31.
    Chen, Yingxian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Assessment of excitation transitions in iodine induced by an orange and a green HeNe laser and its dissociation energy2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This report describes the construction of a laser induced fluorescence(LIF) system based on a grating spectrometer to study the fluorescence spectrum of the Iodine. The measured spectrum was compared to simulated spectra to identify the laser addressed transition. Furthermore the vibrational constants and the dissociation energy of the electronic ground state was extracted using the Birge-Sponer method. For this the Iodine in vapour phase was excited by a green laser with a wavelength corresponding to 18398.7216 cm-1 and orange laser with a wavelength corresponding to 16340.6502 cm-1. For both lasers the iodine molecules were assumed to be excited from the electronic ground state, X10+g, to the excited state, B1u+. The transition energies between the two electronic states were simulated and compared with the laser photon energies to identify possible laser addressed transitions. Further comparisons with values of Doppler width and the simulated and measured rotational splitting of the transitions lead to the conclusions that the iodine is likely to be excited to the ν' = 27, J' = 108 state by the green laser and to the ν' = 9, J' = 50 state by the orange laser. By using the Birge-Sponer method, the values of 1.02 eV for D0 and 2.0 eV for De were found. These values agree within 85% with values given in the literature. The discrepancies between the measurements and simulations based on literature values can most likely be attributed to insufficiently accurate calibration of the spectrometer as well as to higher order terms neglected in the model for the vibrational potential.

  • 32.
    Chen, Zhe
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Realization of resampling for analysis of Fourier transform spectrometer data2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this work, we have constructed a working Fourier Transform Spectrometer (FTS) and realized data acquisition and analyses by re-sampling. The FTS was used to analyze the spectrum of LED. A reference interferogram and measurement interferogram were recorded simultaneously to provide the basis for re-sampling data. The re-sampled data were used to produce spectra with better accuracy and precision. The accuracy of the spectra was in the order of 0.2 nm estimated by the HWHM of the re-sampled reference laser. With no re-sampling the resolution dropped to below 100 nm, for which no useful information could be obtained.

  • 33.
    Cheng, Jialin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Measurement of the temperature in a candle plume using Schlieren photography2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of the experiment was to use Schlieren photography to estimate the temperature in a candle plume. The air temperature of the candle plume was measured by measuring refractive index of air. Schlieren photography was performed, in particular, a Z-type Schlieren setup was implemented. Gladstone-Dale’s law was applied in this experiment to relate the light deviation to the temperature of the candle plume. All the temperature estimation were presented in a two dimensional graph. The estimated range of temperature of candle plume was from 15℃ to 80℃ with error of ±5℃.

  • 34. Chernov, Alexander I
    et al.
    Fedotov, Pavel V
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Suarez Lopez, Inma
    Anoshkin, Ilya V
    Nasibulin, Albert G
    Kauppinen, Esko I
    Obraztsova, Elena D
    Optical properties of graphene nanoribbons encapsulated in single-walled carbon nanotubes2013In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, no 7, p. 6346-6353Article in journal (Refereed)
    Abstract [en]

    We report the photoluminescence (PL) from graphene nanoribbons (GNRs) encapsulated in single-walled carbon nanotubes (SWCNTs). New PL spectral features originating from GNRs have been detected in the visible spectral range. PL peaks from GNRs have resonant character, and their positions depend on the ribbon geometrical structure in accordance with the theoretical predictions. GNRs were synthesized using confined polymerization and fusion of coronene molecules. GNR@SWCNTs material demonstrates a bright photoluminescence both in infrared (IR) and visible regions. The photoluminescence excitation mapping in the near-IR spectral range has revealed the geometry-dependent shifts of the SWCNT peaks (up to 11 meV in excitation and emission) after the process of polymerization of coronene molecules inside the nanotubes. This behavior has been attributed to the strain of SWCNTs induced by insertion of the coronene molecules.

  • 35. Chou, Shao-wei
    et al.
    Xu, J.
    Khrennikov, K.
    Cardenas, Daniel E.
    Wenz, J.
    Heigoldt, M.
    Hofmann, L.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck Institut für Quantenoptik, 85748 Garching, Germany.
    Karsch, S.
    Collective Deceleration of Laser-Driven Electron Bunches2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, no 14, article id 144801Article in journal (Refereed)
    Abstract [en]

    Few-fs electron bunches from laser wakefield acceleration (LWFA) can efficiently drive plasma wakefields (PWFs), as shown by their propagation through underdense plasma in two experiments. A strong and density-insensitive deceleration of the bunches has been observed in 2 mm of 1018 cm−3 density plasma with 5.1 GV=m average gradient, which is attributed to a self-driven PWF. This observation implies that the physics of PWFs, usually relying on large-scale rf accelerators as drivers, can be studied by tabletop LWFA electron sources.

  • 36.
    Dion, Claude
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jonsell, Svante
    Stockholm University.
    Kastberg, Anders
    University of Nice.
    Sjölund, Peder
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bimodal momentum distribution of laser-cooled atoms in optical lattices2016In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, no 5, article id 053416Article in journal (Refereed)
    Abstract [en]

    We study, numerically and experimentally, the momentum distribution of atoms cooled in optical lattices. Using semiclassical simulations, we show that this distribution is bimodal, made up of a central feature corresponding to "cold," trapped atoms, with tails of "hot," untrapped atoms, and that this holds true also for very shallow potentials. Careful analysis of the distribution of high-momentum untrapped atoms, both from simulations and experiments, shows that the tails of the distribution do not follow a normal law, hinting at a power-law distribution and nonergodic behavior. We also revisit the phenomenon leading to the existence of an optimal cooling point, i.e., a potential depth below which the temperature of the atoms starts increasing.

  • 37.
    Dion, Claude
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Keller, A.
    Atabek, O.
    Optimally Controlled Field-Free Orientation of the Kicked Molecule2005In: Physical Review A, Vol. 72, p. 023402-Article in journal (Refereed)
    Abstract [en]

    Efficient and long-lived field-free molecular orientation is achieved using only two kicks appropriately delayed in time. The understanding of the mechanism rests upon a molecular target state providing the best efficiency versus persistence compromise. An optimal control scheme is referred to for fixing the free parameters (amplitudes and the time delay between them). The limited number of kicks, the robustness and the transposability to different molecular systems advocate in favor of the process, when considering its experimental feasibility.

  • 38.
    Dion, Claude M.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Special issue in honour of Andre D. Bandrauk2017In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 115, no 15-16, p. 1729-1729Article in journal (Other academic)
  • 39.
    Dion, Claude M.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sjölund, Peder
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Petra, Stefan J. H.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jonsell, Svante
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kastberg, Anders
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Time dependence of laser cooling in optical lattices2005In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 72, no 3, p. 369-375Article in journal (Refereed)
    Abstract [en]

    We study the dynamics of the cooling of a gas of caesium atoms in an optical lattice, both experimentally and with 1D full-quantum Monte Carlo simulations. We find that, contrary to the standard interpretation of the Sisyphus model, the cooling process does not work by a continuous decrease of the average kinetic energy of the atoms in the lattice. Instead, we show that the momentum of the atoms follows a bimodal distribution, the atoms being gradually transferred from a hot to a cold mode. We suggest that the cooling mechanism should be depicted in terms of a rate model, describing the transfer between the two modes along with the processes occurring within each mode.

  • 40.
    Dion, Claude
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sjölund, Peder
    Umeå University, Faculty of Science and Technology, Physics.
    Petra, Stefan
    Umeå University, Faculty of Science and Technology, Physics.
    Jonsell, Svante
    Umeå University, Faculty of Science and Technology, Physics.
    Nylén, Mats
    Umeå University, Faculty of Science and Technology, Physics.
    Sanchez-Palencia, Laurent
    Kastberg, Anders
    Umeå University, Faculty of Science and Technology, Physics.
    Controllable 3D atomic Brownian motor in optical lattices2008In: The European Physical Journal - Special Topics, ISSN 1951-6355, Vol. 159, no 1, p. 11-17Article in journal (Refereed)
    Abstract [en]

    We study a Brownian motor, based on cold atoms in optical lattices, where atomic motion can be induced in a controlled manner in an arbitrary direction, by rectification of isotropic random fluctuations. In contrast with ratchet mechanisms, our Brownian motor operates in a potential that is spatially and temporally symmetric, in apparent contradiction to the Curie principle. Simulations, based on the Fokker-Planck equation, allow us to gain knowledge on the qualitative behaviour of our Brownian motor. Studies of Brownian motors, and in particular ones with unique control properties, are of fundamental interest because of the role they play in protein motors and their potential applications in nanotechnology. In particular, our system opens the way to the study of quantum Brownian motors.

  • 41. Dombi, Peter
    et al.
    Rácz, Peter
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Baum, Peter
    Conversion of chirp in fiber compression2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 8, p. 2232-2235Article in journal (Refereed)
    Abstract [en]

    Focusing positively chirped femtosecond pulses into nonlinear fibers provides significant spectral broadening and compression at higher pulse energies than achievable conventionally because self-focusing and damage are avoided. Here, we investigate the transfer of input to output chirp in such an arrangement. Our measurements show that the group delay dispersion of the output pulse, originating from the nonlinearities, is considerably reduced as compared to the initial value, by about a factor of 10. The mechanism of chirp reduction is understood by an interplay of self-phase modulation with initial chirp within the fiber. A simple model calculation based on this picture yields satisfactory agreement with the observations and predicts significant chirp reduction for input pulses up to the μJ regime. In practice, the reduction of chirp observed here allows for compressing the spectrally broadened intense pulses by ultrabroadband dispersive multilayer mirrors of quite moderate dispersion.

  • 42. Du, Mingrun
    et al.
    Zhou, Miao
    Yao, Mingguang
    Ge, Peng
    Chen, Shuanglong
    Yang, Xigui
    Liu, Ran
    Liu, Bo
    Cui, Tian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, Jilin University, Changchun, PR China.
    Liu, Bingbing
    High pressure infrared spectroscopy study on C60*CS2 solvates2017In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 669, p. 49-53Article in journal (Refereed)
    Abstract [en]

    High pressure IR study has been carried out on C-60*CS2 solvates up to 34.8 GPa. It is found that the intercalated CS2 molecules significantly affect the transformations of C-60 molecules under pressure. As a probe, the intercalated CS2 molecules can well detect the orientational ordering transition and deformation of C-60 molecules under pressure. The chemical stability of CS2 molecules under pressure is also dramatically enhanced due to the spacial shielding effet from C-60 molecules around in the solvated crystal. These results provide new insight into the effect of interactions between intercalants and fullerenes on the transformations in fullerene solvates under pressure.

    The full text will be freely available from 2019-02-28 09:36
  • 43.
    Dzwilewski, Andrzej
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Photo-induced and resist-free imprint patterning of fullerene materials for use in functional electronics2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 11, p. 4006-4011Article in journal (Refereed)
    Abstract [en]

    We report a novel and potentially generic method for the efficient patterning of films of organic semiconductors and demonstrate the merit of the method on the high-solubility fullerene [6,6]-phenyl C61- butyric acid methyl ester (PCBM). The patterning technique is notably straightforward as it requires no photoresist material and encompasses only two steps: (i) exposure of select film areas to visible laser light during which the PCBM mononer is photochemically converted into a dimeric state, and (ii) development via solvent washing after which the nonexposed portions of the PCBM film are selectively removed. Importantly, the method is highly benign in that it leaves the electronic properties of the remaining patterned material intact, which is directly evidenced by the fact that we fabricate fully functional arrays of micrometersized field-effect transistors with patterned PCBM as the active material.

  • 44.
    Edlund, Adam
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Implementation of continuous filtering frequency comb Vernier spectroscopy for continuous acquisition of spectra in a flame2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this project laser absorption spectroscopy was performed on a flame in a Fabry-Pérot cavity, using an optical frequency comb. Optical frequency comb spectroscopy is a technique that allows broadband ultra-sensitive detection of molecular species in gas phase. Optical frequency combs are generated by femtosecond mode-locked lasers, which generate short pulses and whose spectrum consists of a comb of sharp laser lines covering a broad spectral range. Doing spectroscopy with optical frequency combs can hence be compared to measurements with thousand of synchronised continuous wave lasers simultaneously, which enables broadband sensitive measurements in short acquisition times. A Vernier spectrometer uses the filtering ability of the cavity to allow sequential transmission of parts of the frequency comb spectrum. Its technical simplicity and robustness make it a good candidate for measuring in turbulent environments.

    The aim of the project was to implement continuous-filtering Vernier spectroscopy in a setup for measuring absorption spectra in air and in a flame. This was done by using an Er:fiber femtosecond laser emitting in the near-infrared wavelength range and a Fabry-Pérot cavity containing the flame. The cavity, which consists of two highly reflective mirrors, lets the light of the comb interact with the molecules in the flame for each of the many round-trips it perform; thus increasing the sensitivity to absorption. An active locking mechanism was implemented to stabilize the coupling of the optical frequency comb to the cavity. The locking allowed multiple measurements to be averaged which reduced noise. A galvanometer scanner was added to the system which was used to measure a broad part of the comb spectrum. Hot water absorption lines were detected in the swept comb spectrum and a candidate absorption peak for OH absorption was recorded.

    The spectrometer today has opportunities for improvements. A frequency calibration should be implemented which is essential for making estimates of reactant/product concentrations in combustion processes.

  • 45.
    Edman, Ludvig
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Hérold, A.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Physics.
    Lelaurain, Michelle
    McRae, Edward
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Sodium-sodium halide co-intercalated graphite: chemistry, structure and electrical transport1999In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 60, no 4, p. 475-482Article in journal (Refereed)
    Abstract [en]

    This study deals with the second to fourth stage compounds resulting from the co-intercalation of sodium and sodium halides into graphite. The charge transfer was determined through chemical analyses and X-ray diffraction and the results are compatible with Raman spectroscopy data. We present detailed results on c axis conduction between 4.2 K and 295 K and for hydrostatic pressures as high as 1.6 GPa. Possible mechanisms explaining the c axis conduction are discussed.

  • 46.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Further development of NICE-OHMS: – an ultra-sensitive frequency-modulated cavity-enhanced laser-based spectroscopic
 technique for detection of molecules in gas phase2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy, NICE-OHMS, is a laser-based spectroscopic detection technique that comprises the concepts of frequency modulation (FM, for reduction of 1/f-noise by detecting the signal at a high frequency) and cavity enhancement (CE, for a prolongation of the optical path length) in a unique way. Properly designed, this gives the technique an intrinsic immunity against the frequency-to-noise conversion that limits many other types of CE techniques. All this gives it an exceptionally high sensitivity for detection of molecular species. Although originally developed for frequency standard purposes in the late 1990s, soon thereafter development of the technique towards molecular spectroscopy and trace gas detection was initiated. This thesis focuses on the further development of Doppler- broadened NICE-OHMS towards an ultra-sensitive detection technique. A number of concepts have been addressed. A few of these are: i) The detection sensitivity of fiber-laser-based NICE- OHMS has been improved to the 10−12 cm−1 range, which for detection of C2H2 corresponds to a few ppt (parts-per-trillion, 1:1012) in gas phase, by improving the locking of the laser to a cavity mode by use of an acousto-optic modulator. ii) It is shown that the system can be realized with a more compact footprint by implementation of a fiber-optic circulator. iii) A systematic and thorough investigation of the experimental conditions that provide maximum signals, referred to as the optimum conditions, e.g. modulation and demodulation conditions and cavity length, has been performed. As a part of this, an expression for the NICE-OHMS line shape beyond the conventional triplet formalism has been proposed and verified. iv) To widen the applicability of NICE-OHMS for detection of pressure broadened signals, also a setup based upon a distributed-feedback (DFB) laser has been realized. v) In this regime, the Voigt profile cannot model signals with the accuracy that is needed for a proper assessment of analyte concentrations. Therefore, the thesis demonstrates the first implementations of line profiles encompassing Dicke narrowing and speed-dependent effects to NICE-OHMS. While such profiles are well-known for absorption, there were no expressions available for their dispersion counterparts. Such expressions have been derived and validated by accompanying experiments. vi) The applicability of the technique for elemental detection, then referred to as NICE-AAS, has been prophesied. 

  • 47.
    Ehlers, Patrick
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Use of etalon-immune distances to reduce the influence of background signals in frequency-modulation spectroscopy and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy2014In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 31, no 12, p. 2938-2945Article in journal (Refereed)
    Abstract [en]

    The detection sensitivity of phase-modulated techniques such as frequency-modulation spectroscopy (FMS) and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is often limited by etalon background signals. It has previously been shown that the impact of etalons can be reduced by the use of etalon-immune distances (EIDs), i.e., by separating the surfaces that give rise to etalons by a distance of q. L-m, where L-m is given by c/2n nu(m), where, in turn, n and nu(m) are the index of refraction between the components that make up the etalon (thus most often that of air) and the modulation frequency, respectively, and where q is an integer (i.e., 1, 2, 3,.) or half-integer (i.e., 1/2, 1, 3/2,.) for the dispersion and absorption modes of detection, respectively. An etalon created by surfaces separated by an EID will evade detection and thereby not contribute to any background signal. The concept of EIDs in FMS and NICE-OHMS is in this work demonstrated, scrutinized, and discussed in some detail. It is shown that the influence of EIDs on the absorption and dispersion modes of detection is significantly different; signals detected at the dispersion phase are considerably less sensitive to deviations from exact EID conditions than those detected at the absorption phase. For example, the FM background signal from an etalon whose length deviates from an EID by 2.5% of L-m (e.g., by 1 cm for an L-m of 40 cm), detected in dispersion, is only 9% of that in absorption. This makes the former mode of detection the preferred one whenever a sturdy immunity against etalons is needed or when optical components with parallel surfaces (e.g., lenses, polarizers, or beam splitters) are used. The impact of the concept of EIDs on NICE-OHMS is demonstrated by the use of Allan-Werle plots.

  • 48.
    Ehlers, Patrick
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Doppler broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry: optimum modulation and demodulation conditions, cavity length, and modulation order2014In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 31, no 9, p. 2051-2060Article in journal (Refereed)
    Abstract [en]

    Doppler broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry (Db-NICE-OHMS) has been scrutinized with respect to modulation and demodulation conditions (encompassing the modulation frequency,nu(m), the modulation index, beta, and the detection phase, theta), the cavity length, L, and the modulation order, k (defined as nu(m)/nu(FSR), where nu(FSR) is the free-spectral range of the cavity), primarily in the Doppler limit but also for two specific situations in the Voigt regime (for equal Doppler and homogeneous width and for purely Lorentzian broadened transitions), both in the absence and presence of optical saturation (the latter for the case in which the homogeneous broadening is smaller than the modulation frequency). It is found that, for a system with a given cavity length, the optimum conditions (i.e., those that produce the largest NICE-OHMS signal) for an unsaturated transition in the Doppler limit comprise nu(m)/Gamma(D) = 1.6 (where Gamma(D) is the half-width at half-maximum of the Doppler width of the transition), beta = 1.3, and theta = 0.78 pi. It is also found that the maximum is rather broad; the signal takes 95% of its maximum value for modulation frequencies in the entire 0.4 less than or similar to nu(m)/Gamma(D) less than or similar to 2.4 range. When optical saturation sets in, theta shifts toward the dispersion phase. The optimum conditions encompass k > 1 whenever L > 0.35L(D) and 2.6L(D) for the dispersion and absorption modes of detection, respectively [where L-D is a characteristic length given by c/(2 Gamma(D))]. Similar conditions are found under pressure broadened conditions. 

  • 49.
    Ehlers, Patrick
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry instrumentation for Doppler-broadened detection in the 10-12 cm-1 Hz-1/2 region2012In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 6, p. 1305-1315Article in journal (Refereed)
    Abstract [en]

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

  • 50.
    Ehlers, Patrick
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry incorporating an optical circulator2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 2, p. 279-282Article in journal (Refereed)
    Abstract [en]

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

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