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  • 251.
    Salh, Roushdey
    et al.
    Physics Department, University of Rostock, Universitätsplatz 3, 18051 Rostock, Germany.
    von Czarnowski, A.
    Fitting, H.-J.
    Electron Beam Induced Defects in Ge-implanted SiO2 Layers2005In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 2, p. 580-583Article in journal (Refereed)
  • 252.
    Salh, Roushdey
    et al.
    Institute of Physics, University of Rostock, Universitätsplatz 3, 18051 Rostock, Germany.
    von Czarnowski, A.
    Zamoryanskaya, M. V.
    Kolesnikova, E. V.
    Fitting, H.-J.
    Cathodoluminescence of SiOx under-stoichiometric silica layers2006In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 203, p. 2049-2057Article in journal (Refereed)
  • 253. Salomon, Julien
    et al.
    Dion, Claude
    Umeå University, Faculty of Science and Technology, Physics.
    Turinici, Gabriel
    Optimal molecular alignment and orientation through rotational ladder climbing2005In: Journal of Chemical Physics, Vol. 123, p. 144310-Article in journal (Refereed)
    Abstract [en]

    We study the control by electromagnetic fields of molecular alignment and orientation in a linear, rigid-rotor model. With the help of a monotonically convergent algorithm, we find that the optimal field is in the microwave part of the spectrum and acts by resonantly exciting the rotation of the molecule progressively from the ground state, i.e., by rotational ladder climbing. This mechanism is present not only when maximizing orientation or alignment, but also when using prescribed target states that simultaneously optimize the efficiency of orientation/alignment and its duration. The extension of the optimization method to consider a finite rotational temperature is also presented.

  • 254.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Design and Fabrication of Light-Emitting Electrochemical Cells2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The incandescent light bulb, once the very symbol for human ingenuity, is now being replaced by the next generation of lighting technologies such as the compact fluorescent lamp (CFL) and the light emitting diode (LED). The higher efficiencies and longer operational lifetimes of these new sources of illumination have led to the demise of the classic traditional bulb. However, it should be pointed out that the light sources that are taking over are better, but not perfect. The complex high-voltage electronic circuits and health hazardous materials required for their operation make them far from a sustainable eco-friendly option. Their fabrication is also complex, making the final product expensive. A new path forward might be through the use of plastics or other organic materials. Though not traditionally seen as electronically active, some organic materials do behave like inorganic semiconductors and substantial conductivity can be achieved by doping. Since plastics can be easily molded into complex shapes, or made into an ink using a solvent, it is expected that organic materials could revolutionize how we fabricate electronic devices in the future, and possibly replace inorganic crystals in the same way as plastics have replaced glass and wool for food storage and clothes. This thesis has focused on the light-emitting electrochemical cell (LEC), which was invented by Pei et al. in 1995. It employs organic semiconductors that can convert electricity to light, but also an electrolyte that further enhances the electronic properties of the semiconductor by allowing it to be electrochemically doped. This allows light-emitting films to be driven by a low-voltage source at a high efficiency. Unfortunately, the electrolyte has been shown to facilitate rapid degradation of the device under operation, which has historically severely limited the operational lifetime. Realizing the predicted high efficiency has also proven difficult. The purpose of this thesis is to bridge the gap between the LEC and the CFL. This is done by demonstrating efficient devices and improved operational lifetimes. Possible degradation mechanisms are identified and minimized using novel device architectures and optimized active layer compositions. An encapsulation method is presented, and shown to increase the LEC stability significantly by protecting it from ambient oxygen and water. The thesis further focuses on up-scaled fabrication under ambient air conditions, proving that light-emitting devices are compatible with solution-based and cost-efficient printing. This is achieved by a roll-to-roll compatible slot-die coating and a novel spray-depositing technique that alleviates problems stemming from dust particles and phase separation. A practical ambient air fabrication and a subsequent operation of light-emitting electrochemical cells with high efficiency are thus shown possible.

     

  • 255.
    Sandström, Andreas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Asadpoordarvish, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Enevold, Jenny
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spraying Light: Ambient-Air Fabrication of Large-Area Emissive Devices on Complex-Shaped Surfaces2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 29, p. 4975-4980Article in journal (Refereed)
    Abstract [en]

    Light-emitting electrochemical cells, featuring uniform and efficient light emission over areas of 200 cm(2), are fabricated under ambient air with a for-the-purpose developed "spray-sintering" process. This fault-tolerant fabrication technique can also produce multicolored emission patterns via sequential deposition of different inks based on identical solvents. Significantly, additive spray-sintering using a mobile airbrush allows a straightforward addition of emissive function onto a wide variety of complex-shaped surfaces, as exemplified by the realization of a light-emitting kitchenware fork.

  • 256.
    Sang, Lun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Evaluation of turbulence around a candle plume using Schlieren photography2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Schlieren photography is a widely used technique that can visualize the invisible. The aim of this experiment was to construct a z-type Schlieren setup and photograph the turbulence around the flame of candle. Photos taken were analyzed using FracLac, a plugin of ImageJ. Fractal dimension, morphology and lacunarity were measured. Five photos were used to compare the character and the trend. The nonturbulent pattern had the largest fractal dimension, 1.80. The turbulent patterns had a fractal dimension range from 1.4 to 1.6. One of the patterns affected by a strong breeze had a fractal dimension of 1.3. Though the samples were less, it still revealed the tendency based on fractal dimension. The circularity, lacunarity or density were not a good measure to reveal differences of turbulent patterns and nonturbulent patterns.

  • 257.
    Schedin, Staffan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Pedrini, Giancarlo
    Perez-Lopez, Carlos
    Mendoza Santoyo, Fernando
    Vibration measurements by pulsed digital holographic endoscopy2005In: Eighth international symposium on laser metrology: macro-, micro-, and nano-technologies applied in science, engineering, and industry, Bellingham: SPIE - International Society for Optical Engineering, 2005, p. 729-734Conference paper (Refereed)
    Abstract [en]

    Digital holographic interferometry in combination with a flexible fiber endoscope allows high precision measurements of deformations on hidden objects surfaces, inside cavities and objects with small access apertures. A digital holographic endoscopy system is described with a frequency-doubled, twin oscillator Q-switched pulsed Nd:YAG laser as light source. A sequence of digital hologram pairs are recorded with a maximum repetition rate of 260 ms. Each digital hologram is captured at separate video frames of a CCD-camera. The time separation between the laser pulses from each cavity can be set in the range from 50 to 500 mu s. The digital holograms are transferred to a PC via a frame grabber and evaluated quantitatively by the Fourier transform method. The resulting phase fringe pattern has the information needed to evaluate quantitatively the amount of the deformation. Experimental results of vibration measurements of hidden mechanical and biological object surfaces are presented. The quality of the results obtained by mechanical object surfaces is usually higher than for biological surfaces. This can be explained easily by the fact that a biological surface is much more complex than a mechanical surface in the sense that some parts of the surface may reflect the light well whereas other parts may absorb the light. Also, biological surfaces are translucent, which means that part of the light may enter inside the sample where it may be absorbed or reflected.

  • 258.
    Schmidt, Florian M.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    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.
    Highly sensitive dispersion spectroscopy by probing the free spectral range of an optical cavity using dual-frequency modulation2010In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 101, no 3, p. 497-509Article in journal (Refereed)
    Abstract [en]

    Dual-frequency modulation (DFM) has been used to continuously track the frequency shifts of optical cavity modes in the vicinity of an optical transition of a gas inside the cavity for assessment of the gas concentration. A theoretical description of the size and lineshape of the DFM dispersion spectroscopy (DFM-DS) signal is given. Since the signal is measured in terms of a radio frequency the technique is insensitive to laser intensity fluctuations. The signal strength, which can accurately be obtained by curve fitting, only depends on fundamental parameters (including the line strength), thus enabling quantitative detection without calibration procedure. In a first demonstration, using a compact setup based on a narrowband fiber laser, the change in free spectral range around a value of 379.9 MHz due to an acetylene transition near 1531 nm was measured with a resolution of 6 Hz (i.e. with an accuracy of 1.5 parts in 10(8)) in 12.5 s acquisition time, which corresponds to a minimum detectable integrated absorption (SNR=3) of 3x10(-9) cm(-1)

  • 259.
    Schmidt, Florian M.
    et al.
    University of Helsinki.
    Metsälä, Markus
    Vaittinen, Olavi
    Halonen, Lauri
    Background levels and diurnal variations of hydrogen cyanide in breath and emitted from skin2011In: Journal of Breath Research, ISSN 1752-7163, Vol. 5, no 4, article id 046004Article in journal (Refereed)
    Abstract [en]

    The hydrogen cyanide (HCN) concentration in exhaled human breath and skin gas samples collected with different sampling techniques was measured using near-infrared cavity ring-down spectroscopy. The median baseline HCN concentrations in samples provided by 19 healthy volunteers 2-4 h after the last meal depended on the employed sampling technique: 6.5 parts per billion by volume (ppbv) in mixed (dead space and end-tidal) mouth-exhaled breath collected to a gas sampling bag, 3.9 ppbv in end-tidal mouth-exhaled breath, 1.3 ppbv in end-tidal nose-exhaled breath, 1.0 ppbv in unwashed skin and 0.6 ppbv in washed skin samples. Diurnal measurements showed that elevated HCN levels are to be expected in mouth-exhaled breath samples after food and drink intake, which suggests HCN generation in the oral cavity. The HCN concentrations in end-tidal nose-exhaled breath and skin gas samples were correlated, and it is concluded that these concentrations best reflect systemic HCN levels.

  • 260.
    Schmidt, Florian M.
    et al.
    University of Helsinki.
    Vaittinen, O.
    Metsala, M.
    Kraus, P.
    Halonen, L.
    Direct detection of acetylene in air by continuous wave cavity ring-down spectroscopy2010In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 101, no 3, p. 671-682Article in journal (Refereed)
    Abstract [en]

    Diode laser-based continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared region has been used to measure the mixing ratio of acetylene (C(2)H(2)) in ambient air. Detection limits of 120 parts per trillion by volume (pptv) for 20 min and 340 pptv for 70 s acquisition time were achieved without sample pre-concentration, measuring on a C(2)H(2) absorption line at 6565.620 cm(-1) (similar to 1523 nm). Several indoor and outdoor air samples were collected at different locations in the Helsinki metropolitan area and analyzed using static-cell measurements. In addition, flow measurements of indoor and outdoor air have been performed continuously over several days with a time resolution of down to one minute. Baseline acetylene levels in the range of 0.4 to 3 parts per billion by volume (ppbv), with a maximum around midday and a minimum during the night, were measured. Sudden high mixing ratios of up to 60 ppbv were observed in outdoor air during daytime on a minute time scale. In general, the indoor mixing ratios were found to be higher than those in outdoor air. The acetylene levels correlated with the ambient CO levels and with outdoor temperature.

  • 261. Schmidt, HT
    et al.
    Jensen, J
    Reinhed, P
    Schuch, R
    Stöchkel, Kristian
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Physics, Stockholm University, S-10691 Stockholm, Sweden.
    Zettergren, H
    Cederquist, H
    Bagge, L
    Danared, H
    Källberg, A
    Schmidt-Böcking, H
    Cocke, CL
    Recoil-ion momentum distributions for transfer ionization in fast proton-He collisions2005In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, no 1, article id 012713Article in journal (Refereed)
    Abstract [en]

    We present high-luminosity experimental investigations of the transfer ionization (TI:p+He -> H-0+He2++e(-)) process in collisions between fast protons and neutral helium atoms in the earlier inaccessibly high-energy range 1.4-5.8 MeV. The protons were stored in the heavy-ion storage and cooler ring CRYRING, where they intersected a narrow supersonic helium gas jet. We discuss the longitudinal recoil-ion momentum distribution, as measured by means of cold-target recoil-ion momentum spectroscopy and find that this distribution splits into two completely separated peaks at the high end of our energy range. These separate contributions are discussed in terms of the earlier proposed Thomas TI (TTI) and kinematic TI mechansims. The cross section of the TTI process is found to follow a sigma proportional to v(-b) dependence with b=10.78 +/- 0.27 in accordance with the expected v(-11) asymptotic behavior. Further, we discuss the probability for shake-off accompanying electron transfer and the relation of this TI mechanism to photodouble ionization. Finally the influence of the initial-state electron velocity distribution on the TTI process is discussed.

  • 262. Schwab, M. B.
    et al.
    Sävert, A.
    Jäckel, O.
    Polz, J.
    Schnell, M.
    Rinck, T.
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Möller, M.
    Hansinger, P.
    Paulus, G. G.
    Kaluza, M. C.
    Few-cycle optical probe-pulse for investigation of relativistic laser-plasma interactions2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 19, article id 191118Article in journal (Refereed)
    Abstract [en]

    The development of a few-cycle optical probe-pulse for the investigation of laser-plasma interactions driven by a Ti:sapphire, 30 Terawatt (TW) laser system is described. The probe is seeded by a fraction of the driving laser's energy and is spectrally broadened via self-phase modulation in a hollow core fiber filled with a rare gas, then temporally compressed to a few optical cycles via chirped mirrors. Shadowgrams of the laser-driven plasma wave created in relativistic electron acceleration experiments are presented with few-fs temporal resolution, which is shown to be independent of post-interaction spectral filtering of the probe-beam.

  • 263.
    Segervald, Jonas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fabrication and Optimization of a Nanoplasmonic Chip for Diagnostics2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To increase the survival rate from infectious- and noncommunicable diseases, reliable diagnostic during the preliminary stages of a disease onset is of vital importance. This is not trivial to achieve, a highly sensitive and selective detection system is needed for measuring the low concentrations of biomarkers available. One possible route to achieve this is through biosensing based on plasmonic nanostructures, which during the last decade have demonstrated impressive diagnostic capabilities. These nanoplasmonic surfaces have the ability to significantly enhance fluorescence- and Raman signals through localized hotspots, where a stronger then normal electric field is present. By further utilizing a periodic sub-wavelength nanohole array the extraordinary optical transmission phenomena is supported, which open up new ways for miniaturization.

    In this study a nanoplasmonic chip (NPC) composed of a nanohole array —with lateral size on the order of hundreds of nanometer— covered in a thin layer of gold is created. The nanohole array is fabricated using soft nanoimprint lithography on two resists, hydroxypropyl cellulose (HPC) and polymethyl methacrylate (PMMA). An in depth analysis of the effect of thickness is done, where the transmittance and Raman scattering (using rhodamine 6G) are measured for varying gold layers from 5 to 21 nm. The thickness was proved to be of great importance for optimizing the Raman enhancement, where a maximum was found at 13 nm. The nanohole array were also in general found beneficial for additionally enhancing the Raman signal. A transmittance minima and maxima were found in the region 200-1000 nm for the NPCs, where the minima redshifted as the thickness increased. The extraordinary transmission phenomena was however not observed at these thin gold layers. Oxygen plasma treatment further proved an effective treatment method to reduce the hydrophobic properties of the NPCs. Care needs be taken when using thin layers of gold with a PMMA base, as the PMMA structure could get severely damaged by the plasma. HPC also proved inadequate for this projects purpose, as water-based fluids easily damaged the surface despite a deposited gold layer on top.

  • 264. Sepman, Alexey
    et al.
    Ögren, Yngve
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wiinikka, Henrik
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå University.
    Real-time in situ multi-parameter TDLAS sensing in the reactor core of an entrained-flow biomass gasifier2017In: Proceedings of the Combustion Institute, ISSN 1540-7489, E-ISSN 1873-2704, Vol. 36, no 3, p. 4541-4548Article in journal (Refereed)
    Abstract [en]

    Tunable diode laser absorption spectroscopy (TDLAS) was used to measure several important process parameters at two different locations inside the reactor of an atmospheric, air-blown 0.1 MWth biomass gasifier. Direct TDLAS at 2298 nm was employed for carbon monoxide (CO) and water vapor (H2O), calibration-free scanned wavelength modulation spectroscopy at 1398 nm for H2O and gas temperature, and direct TDLAS at 770 nm for gaseous elemental potassium, K(g), under optically thick conditions. These constitute the first in situ measurements of K(g) and temperature in a reactor core and in biomass gasification, respectively. In addition, soot volume fractions were determined at all TDLAS wavelengths, and employing fixed-wavelength laser extinction at 639 nm. Issues concerning the determination of the actual optical path length, as well as temperature and species non-uniformities along the line-of-sight are addressed. During a 2-day measurement campaign, peat and stem wood powder were first combusted at an air equivalence ratio (lambda) of 1.2 and then gasified at lambdas of 0.7, 0.6, 0.5, 0.4 and 0.35. Compared to uncorrected thermocouple measurements in the gas stream, actual average temperatures in the reactor core were significantly higher. The CO concentrations at the lower optical access port were comparable to those obtained by gas chromatography at the exhaust. In gasification mode, similar H2O values were obtained by the two different TDLAS instruments. The measured K(g) concentrations were compared to equilibrium calculations. Overall, the reaction time was found to be faster for peat than for stem wood. All sensors showed good performance even in the presence of high soot concentrations, and real-time detection was useful in resolving fast, transient behaviors, such as changes in stoichiometry. Practical implications of in-situ TDLAS monitoring on the understanding and control of gasification processes are discussed.

  • 265. Sepman, Alexey
    et al.
    Ögren, Yngve
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wiinikka, Henrik
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Tunable Diode Laser Absorption Spectroscopy Diagnostics of Potassium, Carbon Monoxide, and Soot in Oxygen-Enriched Biomass Combustion Close to Stoichiometry2019In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 11, p. 11795-11803Article in journal (Refereed)
    Abstract [en]

    Combustion facilities run on pulverized biomass often exhibit fluctuations in fuel feeding and, thus, equivalence ratio and would benefit from fast process control based on optical λ sensors installed in the reactor core. The conversion of softwood powder is investigated in an atmospheric entrained-flow reactor (EFR) operated close to stoichiometry using two different burners (swirl and jet) and three oxygen concentrations (21, 30, and 40%). Tunable diode laser absorption spectroscopy (TDLAS) is used to conduct time-resolved (0.1–1 s) in situ measurements of the gas temperature, carbon monoxide (CO), water vapor (H2O), gaseous atomic potassium [K(g)], and soot volume fraction in the lower part of the reactor core and in the exhaust of the EFR. At both locations, the measurement parameters show significant, correlating fluctuations. The local equivalence ratio is derived from a comparison of measured CO and H2O concentrations (for fuel-rich and fuel-lean conditions, respectively) to thermodynamic equilibrium calculations (TEC) and found to vary in a wide range (0.8–1.3). Soot production decreases with an increasing local equivalence ratio and oxygen enrichment and is lower for the swirl compared to the jet burner. The measured K(g) concentrations follow the general behavior predicted by TEC around stoichiometry. In the relevant temperature range (1100–1700 K), K(g) is 2–4 orders of magnitude higher under fuel-rich than fuel-lean conditions, with a sharp transition at stoichiometry. While K(g) concentrations are lower than TEC in the reactor core and under fuel-rich conditions, excellent agreement is found at the exhaust after complete fuel conversion. Precise, wide dynamic range detection of K(g) using TDLAS enables discrimination between fuel-rich and fuel-lean conditions and has the potential for lambda sensing close to the hot reaction zone of combustion plants.

  • 266.
    Seres, Imre Bence
    Umeå University, Faculty of Science and Technology, Department of Physics.
    f to 2f interferometry2017Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    To summarize the work, I succeeded to build an f to 2f interferometer, which is able to handle carrier-envelope phase (CEP) drift measurements. It is operating with two nonlinear effects such as second harmonic generation (SHG), and white light generation. It can measure the change of the CEP from shot to shot, if the shortest integration time of the spectrograph is enough for the repetition rate of the laser system. For CEP stabilizing a high energy, low repetition rate, ultra-short laser system this device can do the required measurements. Even for electric-field-dependent experiments that usually need CEP stabilized laser system, this device helps to provide the measurement without stabilizing the laser system. This is because we can exactly tell the changes of electric field of the laser pulses that are dictating the light-material interaction in the given experiment. Another advantage of this device is that it has relatively small size and mass, so it’s easy to place into many parts of the laser or an experiment, so the electric-field dependence can be investigated easily in several positions. In the near future, when the whole LWS-20 laser system with the double OPCPA stages will be ready for experiments, such as high harmonic generation or electron acceleration, it will be CEP stabilized with the help of this device. At the end of the laser system the repetition rate of the high energy sub-5-fs pulses is 10 Hz, which with an evaluation program written in LabVIEW probably allows to observe the CEP drift in real time. This makes the required long adjusting time in CEP-dependent experiments faster and the accuracy of the measurement better, because the CEP is determined with high accuracy near the experiments.

  • 267.
    Seton, Ragnar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Data acquisition system for optical frequency comb spectroscopy2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Optical Frequency Comb Spectroscopy (OFCS) Group at the Department of Physics at Umeå University develops new techniques for extremely high sensitivity trace gas detection, non invasive temperature measurements, and other applications of OFCS. Their setup used primarily for trace gas detection contains several components that have been developed in-house, including a Fourier Transform Spectrometer (FTS) and an auto-balancing detector. This is the one used in this thesis work and it includes a high frequency data acquisition card (DAC) recording interferograms in excess of 10^7 double-precision floating point samples per sweep of the FTS's retarder. For acquisition and analysis to be possible in both directions of the retarder the interferograms needs to be analysed in a sub-second timeframe, something not possible with the present software. The aim of this thesis work has thus been to develop a system with optimized analysis implementations in MATLAB. The latter was a prerequisite from the group to ensure maintainability, as all members are well acquainted with it.Fulfilling its primary purpose MATLAB performs vector and matrix computations quite efficiently, has mostly fully mutable datatypes, and with recent just-in-time (JIT) compilation optimizations vector resizing performance has improved to what in many instances is perceived as equivalent to preallocated variables. This memory management abstraction, however, also means that explicit control of when arguments are passed by value or by reference to a function is not officially supported. The following performance ramifications naturally increase with the size of the data sets (N) passed as arguments and become quite noticeable even at moderate values of N when dealing with data visualization, a key function in system. To circumvent these problems explicit data references were implemented using some of the undocumented functions of MATLAB's libmx library together with a custom data visualization function.The main parts of the near real time interferogram analysis are resampling and a Fourier transformation, both of which had functionally complete but not optimized implementations. The minimal requirement for the reimplementation of these were simply to improve efficiency while maintaining output precision.On experimentally obtained data the new system's (DAQS) resampling implementation increased sample throughput by a factor of 19 which in the setup used corresponds to 10^8 samples per second. Memory usage was decreased by 72% or in terms of the theoretical minimum from a factor 7.1 to 2.0. Due to structural changes in the sequence of execution DAQS has no corresponding implementation of the reference FFT function as the computations performed in it have been parallelized and/or are only executed on demand, their combined CPU-time can however in a worst-case scenario reach 75% of that of the reference. The data visualization performance increase (compared to MATLAB's own, as the old system used LabVIEW) depends on the size in pixels of the surface it is visualized on and N, decreasing with the former and increasing with the latter. In the baseline case of a default surface size of 434x342 pixels and N corresponding to one full sweep of the FTS's retarder DAQS offers a 100x speed-up to the Windows 7 version of MATLAB R2014b's plot.In addition to acquiring and analyzing interferograms the primary objectives of the work included tools to configure the DAC and controlling the FTS's retarder motor, both implemented in DAQS.Secondary to the above was the implementation of acquisition and analysis for both directions of the retarder, a HITRAN reference spectra generator, and functionality to improve the user experience (UX). The first, though computation time allows for it, has not been implemented due to a delay in the DAC-driver. To provide a generic implementation of the second, the HITRAN database was converted from the text-based format it is distributed in to a MySQL database, a wrapper class providing frequency-span selection and the absorption spectra generation was developed together with a graphical front-end. Finally the improved UX functionality mainly focused on providing easy-access documentation of the properties of the DAC.In summation, though the primary objectives of optimizing the data analysis functions were reached, the end product still requires a new driver for the DAC to provide the full functionality of the reference implementation as the existing one is simply too slow. Many of DAQS' components can however be used as stand-alone classes and functions until a new driver is available. It is also worth mentioning that National Instruments (NI), the DAC vendor, has according to their technical support no plans to develop native MATLAB drivers as MathWorks will not sell them licenses.

  • 268. Shafikov, Marsel Z.
    et al.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bodensteiner, Michael
    Kozhevnikov, Valery N.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    An efficient heterodinuclear Ir(III)/Pt(II) complex: synthesis, photophysics and application in light-emitting electrochemical cells2019In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 34, p. 10672-10682Article in journal (Refereed)
    Abstract [en]

    We report on the design, synthesis, characterization and successful application of a heterodinuclear Ir(III)/Pt(II) complex endowed with two 4,6-diphenylpyrimidine ligands and two acetylacetonate ligands, with one of the former being the rigid bridging unit between the two metal centers. The heterodinuclear complex exhibits red phosphorescence with a high quantum yield of Phi(PL) = 85% and a short room-temperature decay time of tau = 640 ns in degassed toluene solution. The high efficiency of the spin-forbidden T-1 -> S-0 transition is demonstrated to originate in a strong spin-orbit coupling of the T-1 state with a manifold of excited singlet states, which contributes to the record-breaking zero-field splitting of the T-1 state of 240 cm(-1). The high-solubility and non-ionic hetero-dinuclear complex was employed as the emissive guest compound in host-guest light-emitting electrochemical cells, and such optimized devices delivered vibrant red emission (lambda(peak) = 615 nm) with a second-fast turn-on and a high external quantum efficiency of 2.7% at a luminance of 265 cd m(-2).

  • 269. Shahzadi, Iram
    et al.
    Shaukat, Aqsa
    Zara, Zeenat
    Irfan, Muhammad
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ayub, Khurshid
    Iqbal, Javed
    Estimation of optical rotation of gamma-alkylidenebutenolide, cyclopropylamine, cyclopropyl-methanol and cyclopropenone based compounds by a Density Functional Theory (DFT) approach2017In: Chirality, ISSN 0899-0042, E-ISSN 1520-636X, Vol. 29, no 10, p. 634-647Article in journal (Refereed)
    Abstract [en]

    Computing the optical rotation of organic molecules can be a real challenge, and various theoretical approaches have been developed in this regard. A benchmark study of optical rotation of various classes of compounds was carried out by Density Functional Theory (DFT) methods. The aim of the present research study was to find out the best-suited functional and basis set to estimate the optical rotations of selected compounds with respect to experimental literature values. Six DFT functional LSDA, BVP86, CAM-B3LYP, B3PW91, and PBE were applied on 22 different compounds. Furthermore, six different basis sets, i.e., 3-21G, 6-31G, aug-cc-pVDZ, aug-cc-pVTZ, DGDZVP, and DGDZVP2 were also applied with the best-suited functional B3LYP. After rigorous effort, it can be safely said that the best combination of functional and basis set is B3LYP/aug-cc-pVTZ for the estimation of optical rotation for selected compounds.

  • 270.
    Shao, Jie
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Lathdavong, Lemthong
    Umeå University, Faculty of Science and Technology, Physics.
    Thavixay, Phaythoune
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Detection of nitric oxide at low ppb center dot m concentrations by differential absorption spectrometry using a fully diode-laser-based ultraviolet laser system2007In: Journal of the Optical Society of America B, Vol. 24, no 9, p. 2294-2306Article in journal (Refereed)
    Abstract [en]

    An instrumentation for detection of nitric oxide (NO) by direct absorption spectrometry in the parts in 109 (ppb) range on its electronic X2 Pi(v(n) = 0)-A(2)Sigma(+)(v' = 0) transition has been constructed around a commercially available fully diode-laser-based laser system producing milliwatts powers of ultraviolet light at similar to 226.6 run, and its analytical performance has been evaluated. It is shown that the system is capable of detecting NO down to 3 ppb . m under low-pressure conditions (at a signal-to-noise ratio of 3 for a signal averaging of 5s), which is 2 orders of magnitude below that of any other diode-laser-based absorption technique. The combined line strength of the targeted lines was assessed to 3.1 X 10(-18) cm(-1)/(molecule cm(-2)), which supersedes typical line strengths of the fundamental vibrational band and the first and second overtone bands of NO by similar to 2, similar to 4, and similar to 5 orders of magnitude, respectively Also the collision broadening and shift of the targeted lines in NO by N-2 have been assessed.

  • 271.
    Shao, Jie
    et al.
    Institute of Information Optics of Zhejiang Normal University.
    Lathdavong, Lemthong
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Westberg, Jonas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kluczynski, Pawel
    Siemens AB.
    Lundqvist, Stefan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Faraday modulation spectrometry of nitric oxide addressing its electronic X2Π - A2Σ+ band: II. experiment2010In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, no 29, p. 5614-5625Article in journal (Refereed)
    Abstract [en]

    A first demonstration of Faraday modulation spectrometry (FAMOS) of nitric oxide (NO) addressing its strong electronic X2Π(ν″=0)−A2Σ+=0) band is presented. The instrumentation was constructed around a fully diode-laser-based laser system producing mW powers of ultraviolet light targeting the overlapping Q22(21/2) and R12Q(21/2) transitions at ∼226.6nm. The work verifies a new two-transition model of FAMOS addressing the electronic transitions in NO given in an accompanying work. Although the experimental instrumentation could address neither the parameter space of the theory nor the optimum conditions, the line shapes and the pressure dependence could be verified under low-field conditions. NO could be detected down to a partial pressure of 13µTorr, roughly corresponding to 10ppb·m for an atmospheric pressure sample, which demonstrates the feasibility of FAMOS for sensitive detection of NO addressing its strong electronic band. A first demonstration of Faraday modulation spectrometry (FAMOS) of nitric oxide (NO) addressing its srtong electronic X2Π - A2Σ+ band is presented. The instrumentation was constructed around a fully diode-laser-based laser system producing mW powers of ultraviolet light targeting the overlapping Q22(21) and QR12(21) transitions at around 226.6 nm. The work verifies a new two-transition model of FAMOS addressing the electronic transitions in NO given in an accompanying work. Although the experimental instrumentation could address neither the parameter space of the theory nor the optimum conditions, the line shapes and the pressure dependence could be verified under low-field conditions. NO could be detected down to a partial pressure of 13 μTorr, roughly corresponding to 10 ppb · mfor an atmospheric pressure sample, which demonstrates the feasibility of FAMOS for sensitive detection of NO addressing its strong electronic band.

  • 272.
    Shen, Tengjie
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction of a fiber-coupled DFB-laser-based frequency modulated laser radar2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis we construct a fiber-coupled DFB-laser-based frequency modulated coherent laser radar for assessment of distance and velocity of a target. The system is based on an in-fiber Mach-Zehnder heterodyne interferometer. We measure the position of the target in a 60-cm span, with 1.4 mm error and velocity of the target in 2 to 35 mm/s range, with 0.2 mm/s error. The acquisition time for each measurement is around 60 ms for the position measurement and 120 ms for the velocity measurement. Using Allan variance we measure the minimum detection limit of our system for position measurement which is 30 m after 120 s of averaging.

  • 273.
    Shirazi Moogooei, Sahar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterization and Reduction of Background Signals from Etalon Effects in Wavelength Modulation Spectroscopy2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Wavelength Modulation Absorption Spectroscopy (WMAS) is one of the modulation techniques which are used to detect the concentration of the molecules in gas phase. The technique has been of interest for long time due to the cheap equipment and the increase of sensitivity of detection in comparison with Direct Laser Absorption Spectroscopy (DLAS). Although the WMAS demonstrates higher signal to noise ratio than DLAS, the detectability of the technique is often limited by background signals originating from etalon. In this thesis, the set up for both DLAS and WMAS is developed for detection of CO molecules in 600 Torr and transition wavelength 6368.0861 cm-1. In order to characterize the background signals, an etalon with a length of 25 mm, which corresponds to free spectral range of 4 GHz is used. The theoretical description of the technique which is given in terms of Fourier coefficients of modulated absorption lineshape is presented and more over it is illustrated that the amplitude of both analytical signal and background signal has strong dependence on the modulation amplitude ( va ). In order to find the maximum signal to noise ratio (SNR), both the background signals and the analytical signals were scanned and plotted in terms of modulation amplitude. Also the optimum modulation amplitude is chosen to be va opt=3.84 GHz. Therefore it is concluded that for the set up with wavelength modulated distributed feedback (DFB) diode laser, in transition wavelength (6368.0861 cm-1) and in combination with etalon reference (4 GHz FSR), the optimum modulation amplitude which makes the setup etalon free is vFSR= 0.96 (for FSR normalized modulation amplitude) and  va D= 1.9 (for transition width normalized modulation amplitude).

  • 274.
    Shirdel, Mariam
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Probing protein - Pili interactions by optical tweezers and 3D molecular modelling2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 275.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cavity enhanced optical sensing2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    An optical cavity comprises a set of mirrors between which light can be reflected a number of times. The selectivity and stability of optical cavities make them extremely useful as frequency references or discri­mi­nators. With light coupled into the cavity, a sample placed inside a cavity will experience a significantly increased interaction length. Hence, they can be used also as amplifiers for sensing purposes. In the field of laser spectroscopy, some of the most sensitive techniques are therefore built upon optical cavities. In this work optical cavities are used to measure properties of gas samples, i.e. absorption, dispersion, and refractivity, with unprecedented precision.

    The most sensitive detection technique of all, Doppler-broadened noise-immune cavity enhanced optical heterodyne molecular spectrometry (Db NICE-OHMS), has in this work been developed to an ultra-sensitive spectroscopic technique with unprecedented detection sensitivity. By identifying limiting factors, realizing new experimental setups, and deter­mining optimal detection conditions, the sensitivity of the technique has been improved several orders of magnitude, from 8 × 10-11 to 9 × 10-14 cm-1. The pressure interval in which NICE-OHMS can be applied has been extended by deri­vation and verification of dispersions equations for so-called Dicke narrowing and speed dependent broadening effects. The theoretical description of NICE-OHMS has been expanded through the development of a formalism that can be applied to the situations when the cavity absorption cannot be considered to be small, which has expanded the dynamic range of the technique. In order to enable analysis of a large number of molecules at their most sensitive transitions (mainly their funda­mental CH vibrational transitions) NICE-OHMS instrumentation has also been developed for measurements in the mid-infrared (MIR) region. While it has been difficult to realize this in the past due to a lack of optical modulators in the MIR range, the system has been based on an optical para­metric oscillator, which can be modulated in the near-infrared (NIR) range.

    As the index of refraction can be related to density, it is possible to retrieve gas density from measurements of the index of refraction. Two such instru­men­tations have been realized. The first one is based on a laser locked to a measure­ment cavity whose frequency is measured by compassion with an optical frequency comb. The second one is based on two lasers locked to a dual-cavity (i.e. one reference and one measurement cavity). By these methods changes in gas density down to 1 × 10-9 kg/m3 can be detected.

    All instrumentations presented in this work have pushed forward the limits of what previously has been considered measurable. The knowledge acquired will be of great use for future ultrasensitive cavity-based detection methods.

  • 276.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    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.
    Frequency modulation background signals from fiber-based electro optic modulators are caused by crosstalk2012In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 5, p. 916-923Article in journal (Refereed)
    Abstract [en]

    Frequency modulated spectroscopy (FMS) performed by the use of fiber-coupled electro optic modulators (FC-EOMs) is often plagued by background signals that bring in noise and, by their temperature dependence, cause severe drifts. These signals cannot be zeroed out by the conventional technique of using a carefully adjusted polarizer that can be applied to free space electro optic modulators (EOMs). This can limit the use of FC-EOMs in high performance detection techniques. Here we provide an explanation to these background signals that is based upon crosstalk between various polarization directions of light in the fixed mounted polarization-maintaining fibers and the electro optic crystal. The description provides a basis for the previously demonstrated technique that utilizes an EOM regulated simultaneously by temperature and DC voltage to eliminate background signals from systems encompassing FC-EOMs. (C) 2012 Optical Society of America

  • 277.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Model for in-coupling of etalons into signal strengths extracted from spectral line shape fitting and methodology for predicting the optimum scanning range: demonstration of Doppler-broadened, noise-immune, cavity-enhanced optical heterodyne molecular spectroscopy down to 9  ×  10−14 cm−12015In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 32, no 10, p. 2104-2114Article in journal (Refereed)
    Abstract [en]

    Expressions for the in-coupling of white noise and etalons into fitted signal strengths are derived. These show that the amount of noise picked up is affected by the scanning range. A methodology for finding the optimum scanning range from a single set of measurements has been developed. This was used to estimate the optimum conditions of a noise-immune, cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) setup. The methodology was validated by measurements. This resulted in a spectral noise equivalent absorption per unit length of 2.6 × 10−13 cm−1 Hz−1∕2 and a minimum Allan deviation of 9 × 10−14 cm−1 at 30 s, which are, to our knowledge, the lowest reported for Doppler-broadened NICE-OHMS

  • 278.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    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 down to 4 x 10-13 cm-1 Hz-1/2: implementation of a 50,000 finesse cavity2015In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 9, p. 2004-2007Article in journal (Refereed)
    Abstract [en]

    We report on the realization of a Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) instrumentation based on a high-finesse (50,000) cavity with a detection sensitivity of 4 x 10(-13) cm(-1) Hz(-1/2). For the P-e(11) transition targeted at 1.5316 mu m, this corresponds to a C2H2 concentration of 240 ppq (parts-per-quadrillion) detected at 100 Torr. The setup was originally affected by recurrent dips in the cavity transmission, which were attributed to excitation of high-order transverse mode by scattering from the mirrors. The effect of these was reduced by insertion of a small pinhole in the cavity.

  • 279.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Harren, Frans J. M.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Doppler-broadened mid-infrared noise-immune cavity-enhanced optical heterodyne molecular spectrometry based on an optical parametric oscillator for trace gas detection2015In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 4, p. 439-442Article in journal (Refereed)
    Abstract [en]

    An optical parametric oscillator based Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) system suitable for addressing fundamental vibrational transitions in the 3.2-3.9 mu m mid-infrared (MIR) region has been realized. An Allan-Werle analysis provides a detection sensitivity of methane of 1.5 x 10-9 cm(-1) with a 20 s integration time, which corresponds to 90 ppt of CH4 if detected at the strongest transition addressed at 40 Torr. This supersedes that of previous Db MIR NICE-OHMS demonstrations and suggests that the technique can be suitable for detection of both the environmentally important (CH4)-C-13 and CH3D isotopologues. It also opens up for detection of many other molecular species at ppt and sub-ppt concentration levels.

  • 280.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A dual Fabry-Perot cavity for fast assessments of gasnumber densityManuscript (preprint) (Other academic)
  • 281.
    Sjögren, Adam
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The impact of metallic cranial implants on proton-beam radiotherapy treatment plans for near implant located tumours: A phantom study on the physical effects and agreement between simulated treatment plans and the resulting treatment for near implant located cranial tumours2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Within the field of radiotherapy treatments of tumour diseases, the hunt for more accurate and effective treatment methods is a continuous process. For some years ion-beam based radiotherapy, especially the proton-beam based applications, has increased in popularity and availability. The main reason behind this is the fact that ion-beam based applications make it possible to modulate the dose after the planning target volume (PTV) defined by the radiation oncologist. This means that it becomes possible to spare tissue in another way, which might result in more effective treatments, especially in the vicinity of radio sensitive organs. Ion-beam based treatments are however more sensitive to uncertainties in PTV position and beam range as ion-beams have a fixed range depending on target media and initial energy, as opposed to the conventional x-ray beams that do not really have a defined range. Instead their intensity decreases exponentially at a rate dependent of the initial energy and target media. Therefore density heterogeneities result in uncertainties in the planned treatments. As the plans normally are created using a CT-images, for which metallic implants can yield increased heterogeneities both from the implants themselves and so called metal artifacts (distortions in the images caused by different processes as the X-rays used in image acquisition goes through metals). Metallic implants affects the accuracy of a treatment, and therefore also the related risks, so it is important to have an idea of the magnitude of the impact. Therefore the aim of this study is to estimate the impact on a proton-beam based treatment plan for six cranial implants. These were one Ti-mesh implant, one temporal plate implant, one burr-hole cover implant and three craniofix implants of different sizes, which all are commonly seen at the Skandion clinic. Also the ability of the treatment planning system (TPS), used at the clinic, to simulate the effects on the plans caused by the implants is to be studied. From this result it should be estimated if the margins and practices in place at the clinic, for when it is required to aim the beam through the implant, are sufficient or if they should be changed.

    This study consisted of one test on the range shift effects and one test on the lateral dose distribution changes, with one preparational test in the form of a calibration of Gafchromic EBT3 films. The range shift test was performed on three of the implants, excluding the three craniofix implants using a water phantom and a treatment plan created to represent a standard treatment in the cranial area. The lateral dose distribution change test was performed as a solid phantom study using radiochromic film, for two treatment plans (one where the PTV was located \SI{2}{\centi\metre} below surface, for all implants, and one where it was located at the surface, only for the Ti-mesh and the temporal plate). The results of both tests were compared to simulations performed in the Eclipse treatment planing system (TPS) available at Skandion.

    The result of the range shift test showed a maximum range shift of \SI{-1.03 +- 0.01}{\milli\metre}, for the burr-hole cover implant, and as the related Eclipse simulations showed a maximal shift of \SI{-0.17 +- 0.01}{\milli\metre} there was a clear problem with the simulation. However, this might not be because of the TPS but due to errors in the CT-image reconstruction, such as, for example, geometrical errors in the representation of the implants. As the margin applied for a similar situation at the Skandion clinic (in order to correct for several uncertainty factors) is \SI{4.2}{\milli\metre} there might be a need to increase this margin depending on the situation.

    For the lateral distribution effects no definite results were found as the change varied in magnitude, even if it tended to manifest as a decreasing dose for the first plan and a increasing dose for the second. It was therefore concluded that further studies are needed before anything clear can be said.

  • 282.
    Sjölund, Peder
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Laser cooling mechanisms and Brownian motors in optical lattices2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, detailed experimental studies and numerical simulations are presented of laser cooling mechanisms in dissipative optical lattices and results of the first realized three dimensional Brownian motor in optical lattices. A dissipative optical lattice is a periodic light shift potential, created in the interference patterns of laser beams. In this, atoms can be both cooled and trapped, and the most important relaxation mechanism is generally considered to be “Sisyphus cooling”. However, careful experimental and theoretical investigations indicate the presence of other cooling processes as well. This is studied by varying different parameters such as irradiance and frequency of the lattice light. The time evolution of atoms in optical lattices show strong evidence of a bimodal velocity distribution, where a population transfer between one mode containing “hot” atoms and one mode containing “cold” atoms is evident. The normal diffusion of atoms in optical lattices is characterized by isotrop random fluctuations and exhibit the nature of Brownian motion. We have realized a technique where this motion is rectified and controlled. This is done in a three dimensional double optical lattice. This Brownian motor has control properties for both its speed and its direction in three dimensions. Our three dimensional double optical lattice is created by using laser light, exploiting two transitions, in the D2 line of cesium. Two three dimensional optical lattices are spatially overlapped; each optical lattice traps atoms in one of two hyperfine ground states. The controllability comes about by inducing phase shifts in the lattice laser beams, which displace the lattices relative to each other. This type of highly controlled Brownian motor is of fundamental interest since Brownian motion is present in almost all systems and for the role they play in protein motors and the function of living cells, and for the potential applications in nanotechnology. Brownian motors of this kind also open the way to possible studies of quantum Brownian motors and quantum resonances that are predicted for atomic ratchets. Optical lattices, and especially double optical lattices, have also been suggested as a platform for quantum state manipulations due to the good isolation from environment and ambient effects. Most of the work in this thesis is a first step towards the implementation of quantum manipulation schemes in a double optical lattice.

  • 283.
    Sjölund, Peder
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Petra, Stefan J.H.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dion, Claude
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hagman, Henning
    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.
    Characterisation of a three-dimensional Brownian motor in optical lattices2007In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 44, no 2, p. 381-388Article in journal (Refereed)
    Abstract [en]

    We present here a detailed study of the behaviour of a three dimensional Brownian motor based on cold atoms in a double optical lattice [P. Sjölund et al., Phys. Rev. Lett. 96, 190602 (2006)]. This includes both experiments and numerical simulations of a Brownian particle. The potentials used are spatially and temporally symmetric, but combined spatiotemporal symmetry is broken by phase shifts and asymmetric transfer rates between potentials. The diffusion of atoms in the optical lattices is rectified and controlled both in direction and speed along three dimensions. We explore a large range of experimental parameters, where irradiances and detunings of the optical lattice lights are varied within the dissipative regime. Induced drift velocities in the order of one atomic recoil velocity have been achieved.

  • 284.
    Sjölund, Peder
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Petra, Stefan J.H.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dion, Claude
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jonsell, Svante
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nylén, Mats
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sanchez-Palencia, L.
    Laboratoire Charles Fabry de l’Institut d’Optique, CNRS and Université Paris-Sud XI, France.
    Kastberg, Anders
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Demonstration of a controllable three-dimensional Brownian motor in symmetric potentials2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, no 19, p. 190602-Article in journal (Refereed)
    Abstract [en]

    We demonstrate a Brownian motor, based on cold atoms in optical lattices, where isotropic random fluctuations are rectified in order to induce controlled atomic motion in arbitrary directions. In contrast to earlier demonstrations of ratchet effects, our Brownian motor operates in potentials that are spatially and temporally symmetric, but where spatiotemporal symmetry is broken by a phase shift between the potentials and asymmetric transfer rates between them. The Brownian motor is demonstrated in three dimensions and the noise-induced drift is controllable in our system.

  • 285.
    Skogeby, Richard
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Performance assessment of fluorescent nuclear track detectors in physically optimised spread-out Bragg peaks: Carried out at the German Cancer Research Center2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Clinical heavy ion beams provide the most accurate means of external radiation treatment of tumors available. The study of energetic heavy ions on individual cells have been hampered by shortcomings in available detector technology. The fluorescence nuclear track detector developed by the Landauer Inc. is a small chiplike detector with all the properties needed for these kinds of studies. It is biocompatible, autoclavable, does not require post-irradiation chemical processingand allows the readout of a sufficient number of physical parameters for the determination of a particle’s radiobiological and physical properties. Previous studies in clinical spread-out Bragg peaks have shown a discrepancy in what is detected to what is seen in Monte Carlo radiation transport simulations. While the fluence of heavy primary ions agrees to within one percent, the detection of fragments is underestimated by at least an order of magnitude.

    In this thesis the performance of the track-recording has been assessed for light ion fragmentsfrom hydrogen, helium and carbon primary particles in physically optimised spread-out Braggpeaks. The underestimation of light ion fragments for carbon beams, mentioned in previousstudies, was reproduced. The underestimation of light ion fragments is prevalent also for helium primary particles. No significant amount of lost tracks are seen in hydrogen beams. The analysis verifies the hypothesis that the detection of large angle trajectories for light ion fragments is not a principal limitation of the detector. The underestimation most probably stems from some limiting features of the readout and image analysis procedure.

  • 286.
    Skrypnychuk, Vasyl
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wetzelaer, Gert-Jan A. H.
    Gordiichuk, Pavlo I.
    Mannsfeld, Stefan C. B.
    Herrmann, Andreas
    Toney, Michael F.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ultrahigh Mobility in an Organic Semiconductor by Vertical Chain Alignment2016In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 28, no 12, p. 2359-2366Article in journal (Refereed)
    Abstract [en]

    A method to produce highly efficient and long-range vertical charge transport is demonstrated in an undoped polythiophene thin film, with average mobilities above 3.1 cm(2) V-1 s(-1). These record high mobilities are achieved by controlled orientation of the polymer crystallites enabling the most efficient and fastest charge transport along the chain backbones and across multiple chains. The significant increase in mobility shown here may present a new route to producing faster and more efficient optoelectronic devices based on organic materials. [GRAPHICS] .

  • 287.
    Smijesh, N.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, X.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fischer, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Muschet, Alexander
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Salh, Roushdey
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tajalli, A.
    Morgner, U.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Contrast improvement of sub-4 fs laser pulses using nonlinear elliptical polarization rotation2019In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 44, no 16, p. 4028-4031Article in journal (Refereed)
    Abstract [en]

    Temporal-intensity contrast is crucial in intense laser-matter interaction to circumvent the undesirable expansion of steep high-density plasma prior to the interaction with the main pulse. Nonlinear elliptical polarization rotation in an argon filled hollow-core fiber is used here for cleaning pedestals/satellite pulses of a chirped-pulse-amplifier based Ti: Sapphire laser. This source provides similar to 35 mu J energy and sub-4-fs duration, and the process has >50% internal efficiency, more than the most commonly used pulse cleaning methods. Further, the contrast is improved by 3 orders of magnitude when measured after amplifying the pulses to 16 TW using non-collinear optical parametric chirped pulse amplification with a prospect to even further enhancement.

  • 288.
    Sobon, Grzegorz
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Laser & Fiber Electronics Group, Faculty of Electronics, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland.
    Martynkien, Tadeusz
    Mergo, Pawel
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-power frequency comb source tunable from 2.7 to 4.2 mu m based on difference frequency generation pumped by an Yb-doped fiber laser2017In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 9, p. 1748-1751Article in journal (Refereed)
    Abstract [en]

    We demonstrate a broadband mid-infrared (MIR) frequency comb source based on difference frequency generation (DFG) in periodically poled lithium niobate crystal. MIR radiation is obtained via mixing of the output of a 125 MHz repetition rate Yb-doped fiber laser with Raman-shifted solitons generated from the same source in a highly nonlinear fiber. The resulting idler is tunable in the range of 2.7-4.2 mu m, with average output power reaching 237 mW and pulses as short as 115 fs. The coherence of the MIR comb is confirmed by spectral interferometry and heterodyne beat measurements. Applicability of the developed DFG source for laser spectroscopy is demonstrated by measuring absorption spectrum of acetylene at 3.0-3.1 mu m. (C) 2017 Optical Society of America

  • 289.
    Soboń, Grzegorz
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Faculty of Electronics, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland .
    Martynkien, Tadeusz
    Mergo, Pawel
    Marangoni, Marco
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-power broadband source tunable from 2.8 to 4 μm based on difference frequency generation2017In: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Mid-infrared (MIR) frequency comb sources enable high-speed and accurate detection of various species, since many molecules possess their fingerprints in this wavelength range. Usually, broadband radiation in this spectral region is obtained from optical parametric oscillators (OPOs), which provide high output power and broad tuning capabilities [1]. However, OPO sources require locking of the cavity to the pumping oscillator, which increases the complexity. MIR sources based on difference frequency generation (DFG) are interesting alternatives to OPOs, due to their simplicity, single-pass configuration, broad tunability, and fully passive cancellation of the carrier-envelope offset in the generated idler pulses. However, the conversion efficiency of the DFG process is usually insufficient to reach the output power levels easily achieved in OPO systems. Here, we demonstrate a widely tunable DFG source based on a mode-locked Yb-doped fiber laser, with average MIR output power reaching 165 mW, which is more than in previous reports on similar DFG systems [2,3].

  • 290.
    Soleimani, Saeedeh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Design of a Tele-objective Zoom Lens and an Instrumentation for Assessment of Distances2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Since the zoom lens was introduced, the right selection of the zoom lenses for a given condition has been a controversial decision. The Design of a good optical structure while keeping a balance between cost, magnification, zoom range and weight is challenging for optical engineers. This project describes and simulates two-zoom-lens-structures with four to five groups of lenses. One of the zoom-lens-structure is based on the Cook triplet design with four lenses and floating aperture. To achieve the desired requirement, the zoom lens comprises four group lenses of which three are movable. To provide zooming, the aperture stop is considered floating. The final system meets a set of preferred zoom lens camera characteristics like a sharp image, minimum aberration, reduced length of camera body and high zoom. Moreover, an instrument for distance measurement is designed. It is based on the method of minimization of astigmatism. By tilting some of the lenses, an optical system is designed with three high refractive power lenses that provides large amount of astigmatism. Finally, based on the results from spot diagram for tangential and sagittal focuses, a forth order polynomial function is introduced which can be used for calibration of the system.

  • 291.
    Stangner, Tim
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Svenmarker, Pontus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Oddershede, Lene B.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cooke-Triplet-Tweezers: More compact, robust and efficient optical tweezers2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 9, p. 1990-1993Article in journal (Refereed)
    Abstract [en]

    We present a versatile three-lens optical design to improve the overall compactness, efficiency, and robustness for optical tweezers based applications. The design, inspired by the Cooke–Triplet configuration, allows for continuous beam magnifications of 2–10× , and axial as well as lateral focal shifts can be realized without switching lenses or introducing optical aberrations. We quantify the beam quality and trapping stiffness and compare the Cooke–Triplet design with the commonly used double Kepler design through simulations and direct experiments. Optical trapping of 1 and 2 μm beads shows that the Cooke–Triplet possesses an equally strong optical trap stiffness compared to the double Kepler lens design but reduces its lens system length by a factor of 2.6. Finally, we demonstrate how a Twyman–Green interferometer integrated in the Cooke–Triplet optical tweezers setup provides a fast and simple method to characterize the wavefront aberrations in the lens system and how it can help in aligning the optical components perfectly.

  • 292.
    Stangner, Tim
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hanqing, Zhang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tobias, Dahlberg
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Krister, Wiklund
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Step-by-step guide to reduce spatial coherence of laser light using a rotating ground glass diffuser2017In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 56, no 19, p. 5427-5435Article in journal (Refereed)
    Abstract [en]

    Wide field-of-view imaging of fast processes in a microscope requires high light intensities motivating the use of lasers as light sources. However, due to their long spatial coherence length, lasers are inappropriate for such applications, as they produce coherent noise and parasitic reflections, such as speckle, degrading image quality. Therefore, we provide a step-by-step guide for constructing a speckle-free and high-contrast laser illumination setup using a rotating ground glass diffuser driven by a stepper motor. The setup is easy to build, cheap, and allows a significant light throughput of 48%, which is 40% higher in comparison to a single lens collector commonly used in reported setups. This is achieved by using only one objective to collect the scattered light from the ground glass diffuser. We validate our setup in terms of image quality, speckle contrast, motor-induced vibrations, and light throughput. To highlight the latter, we record Brownian motion of micro-particles using a 100x oil immersion objective and a high-speed camera operating at 2000 Hz with a laser output power of only 22 mW. Moreover, by reducing the objective magnification to 50x, sampling rates up to 10,000 Hz are realized. To help readers with basic or advanced optics knowledge realize this setup, we provide a full component list, 3D-printing CAD files, setup protocol, and the code for running the stepper motor.

  • 293.
    Sundararaj, Amruthaa
    Umeå University, Faculty of Science and Technology, Department of Physics. SRM University.
    Fast Fourier Transform Spectrum Analyzer: Construction of a Fast Fourier Transform Spectrometer and Analysing Characteristic Spectrum of Light Emitting Diodes2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this work a Fast Fourier Transform (FFT) spectrometer with a He-Ne laser as a reference is constructed from "off-the-shelf components" to investigate the spectrum of high luminescent diodes. The resolution of the spectrometer was calculated to be 4.7 GHz and the measured spectra were in accordance with the diodes specifications. The diodes measured were B42182 and N42182 of Seoul Semiconductors whose band gap and composition was determined based on the information from their characteristic emission spectrum.

  • 294. Svanqvist, Mattias
    et al.
    Glimtoft, Martin
    Ågren, Matilda
    Nordberg, Markus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Östmark, Henric
    Stand-off detection of explosives and precursors using compressive sensing Raman spectroscopy2016In: Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XVII / [ed] Augustus W. Fountain, SPIE - International Society for Optical Engineering, 2016, article id UNSP 98240CConference paper (Refereed)
    Abstract [en]

    We present initial results on the performance of a compressive sensing setup for Raman imaging spectroscopy for standoff trace explosives detection. Hyperspectral image reconstruction is demonstrated under low signal conditions and successful spatial separation of substances with close lying Raman peaks is shown.

  • 295.
    Svensson, Fredrik
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Jonsell, Svante
    Dion, Claude
    Umeå University, Faculty of Science and Technology, Physics.
    Simulations of Sisyphus cooling including multiple excited states2008In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 48, no 2, p. 235-240Article in journal (Refereed)
    Abstract [en]

    We extend the theory for laser cooling in a near-resonant optical lattice to include multiple excited hyperfine states. Simulations are performed treating the external degrees of freedom of the atom, i.e., position and momentum, classically, while the internal atomic states are treated quantum mechanically, allowing for arbitrary superpositions. Whereas theoretical treatments including only a single excited hyperfine state predict that the temperature should be a function of lattice depth only, except close to resonance, experiments have shown that the minimum temperature achieved depends also on the detuning from resonance of the lattice light. Our results resolve this discrepancy.

  • 296.
    Tan, Jeryl
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Forget, Nicolas
    Borot, Antonin
    Kaplan, Daniel
    Tournois, Pierre
    Muschet, Alexander
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Dispersion control for temporal contrast optimization2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 19, p. 25003-25012Article in journal (Refereed)
    Abstract [en]

    We investigate the temporal contrast of the Light Wave Synthesizer 20 (LWS-20): a powerful, few-cycle source based on the optical parametric synthesizer principle. Saturation effects in the RF amplifier driving the acousto-optic programmable dispersive filter (AOPDF) were found to degrade the coherent contrast for non-monotonic group delay corrections. We subsequently present a new dispersion scheme and design a novel transmission grism-based stretcher optimized for LWS-20. The resulting temporal contrast of the amplified, compressed output pulses is improved by 2-4 orders of magnitude compared to the former design.

  • 297.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    Murto, Petri
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    Andersson, Mats R.
    Wang, Ergang
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    On the Design of Host-Guest Light-Emitting Electrochemical Cells: Should the Guest be Physically Blended or Chemically Incorporated into the Host for Efficient Emission?2019In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 7, no 18, article id 1900451Article in journal (Refereed)
    Abstract [en]

    It has recently been demonstrated that light‐emitting electrochemical cells (LECs) can be designed to deliver strong emission with high efficiency when the charge transport is effectuated by a majority host and the emission is executed by a minority guest. A relevant question is then: should the guest be physically blended with or chemically incorporated into the host? A systematic study is presented that establishes that for near‐infrared‐(NIR‐) emitting LECs based on poly(indacenodithieno[3,2‐b]thiophene) (PIDTT) as the host and 4,7‐bis(4,4‐bis(2‐ethylhexyl)‐4H‐silolo[3,2‐b:4,5‐b′]dithiophen‐2‐yl)benzo[c][1,2,5]‐thiadiazole (SBS) as the guest the chemical‐incorporation approach is preferable. The host‐to‐guest energy transfer in LEC devices is highly efficient at a low guest concentration of 0.5%, whereas guest aggregation and ion redistribution during device operation severly inhibits this transfer in the physical‐blend devices. The chemical‐incorporation approach also results in a redshifted emission with a somewhat lowered photoluminescence quantum yield, but the LEC performance is nevertheless very good. Specifically, an NIR‐LEC device comprising a guest‐dilute (0.5 molar%) PIDTT‐SBS copolymer delivers highly stabile operation at a high radiance of 263 µW cm−2 (peak wavelength = 725 nm) and with an external quantum efficiency of 0.214%, which is close to the theoretical limit for this particular emitter and device geometry.

  • 298.
    Tang, Shi
    et al.
    The Organic Photonics and Electronics Group, Umeå University: LunaLEC AB, Umeå University, Umeå, Sweden Umeå, Sweden Umeå, Sweden.
    Murto, Petri
    Wang, Jia
    The Organic Photonics and Electronics Group, Umeå University, Umeå, Sweden.
    Larsen, Christian
    The Organic Photonics and Electronics Group, Umeå University; LunaLEC AB, Umeå University, Umeå, Sweden Umeå, Sweden Umeå, Sweden.
    Andersson, Mats R.
    Wang, Ergang
    Edman, Ludvig
    The Organic Photonics and Electronics Group, Umeå University; LunaLEC AB, Umeå University, Umeå, Sweden Umeå, Sweden.
    On the Design of Host-Guest Light-Emitting Electrochemical Cells: Should the Guest be Physically Blended or Chemically Incorporated into the Host for Efficient Emission?2019In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 7, no 18, article id 1900451Article in journal (Refereed)
    Abstract [en]

    It has recently been demonstrated that light-emitting electrochemical cells (LECs) can be designed to deliver strong emission with high efficiency when the charge transport is effectuated by a majority host and the emission is executed by a minority guest. A relevant question is then: should the guest be physically blended with or chemically incorporated into the host? A systematic study is presented that establishes that for near-infrared-(NIR-) emitting LECs based on poly(indacenodithieno[3,2-b]thiophene) (PIDTT) as the host and 4,7-bis(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b ']dithiophen-2-yl)benzo[c][1,2,5]-thiadiazole (SBS) as the guest the chemical-incorporation approach is preferable. The host-to-guest energy transfer in LEC devices is highly efficient at a low guest concentration of 0.5%, whereas guest aggregation and ion redistribution during device operation severly inhibits this transfer in the physical-blend devices. The chemical-incorporation approach also results in a redshifted emission with a somewhat lowered photoluminescence quantum yield, but the LEC performance is nevertheless very good. Specifically, an NIR-LEC device comprising a guest-dilute (0.5 molar%) PIDTT-SBS copolymer delivers highly stabile operation at a high radiance of 263 mu W cm(-2) (peak wavelength = 725 nm) and with an external quantum efficiency of 0.214%, which is close to the theoretical limit for this particular emitter and device geometry.

  • 299. Teichmann, S. M.
    et al.
    Racz, P.
    Ciappina, M. F.
    Perez-Hernandez, J. A.
    Thai, A.
    Fekete, J.
    Elezzabi, A. Y.
    Veisz, László
    Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Biegert, J.
    Dombi, P.
    Strong-field plasmonic photoemission inthe mid-IR at <1 GW/cm2 intensity2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 7584Article in journal (Refereed)
    Abstract [en]

    We investigated nonlinear photoemission from plasmonic films with femtosecond, mid-infrared pulses at 3.1 μm wavelength. Transition between regimes of multi-photon-induced and tunneling emission is demonstrated at an unprecedentedly low intensity of <1 GW/cm2. Thereby, strong-field nanophysics can be accessed at extremely low intensities by exploiting nanoscale plasmonic field confinement, enhancement and ponderomotive wavelength scaling at the same time. Results agree well with quantum mechanical modelling. Our scheme demonstrates an alternative paradigm and regime in strong-field physics.

  • 300.
    Tengberg, Oskar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Construction and Optimization of an Apparatus for Detection of Nitric Oxide through Faraday Modulation Spectroscopy2015Independent thesis Advanced level (degree of Master (Two Years)), 300 HE creditsStudent thesis
    Abstract [en]

    Faraday modulation spectroscopy (FAMOS) is a technique for detection of paramagnetic molecules. By applying a magnetic field over a gaseous sample, the presence of paramagnetic species will rotate the polarization plane of light, addressing a transition in such a species. By placing a gas containing paramagnetic molecules between almost crossed polarizers and modulating the magnetic field, the intensity of the transmitted light will consequently be modulated. Since the rotation of the polarization plane of light is proportional to the concentration of species, this technique can be used for quantitative analysis of paramagnetic molecules.

    Since FAMOS is solely sensitive to paramagnetic molecules it is superior to many other types of laser-based detection techniques, drastically decreasing various types of noise, background signals, as well as signals from other molecules; e.g. flicker noise, etalon effects and signals from water and CO2 molecules.

    An experimental setup for detection of nitric oxide (NO) by FAMOS has been developed and optimized. This system is based on a quantum cascade laser emitting light at 5.331 μm, addressing the—for FAMOS—most sensitive transition in NO, Q3/2(3/2). Optimized parameters include a pressure of 60 mbar, a magnetic field of 190 G and a polarizer uncrossing angle of 0.75°.

    In its present configuration, this system has demonstrated a detection of NO down to 200 ppb for a detection rate of 10 measurements per second. It is very possible that the limit of detection is even lower than this number since this lowest acquirable concentration is limited by the specifications of the gas mixer. A standard deviation between subsequent measurements, of 15 s time separation, is calculated to 30 ppb. However, this is far from the expected ultimate detection limit of this system and this technique in general.

    One process that causes a weakening of the signal is outgassing. When measuring on an emptied system this phenomenon is greatly reduced and a standard deviation of measurements is then measured and calculated to 7.6 ppb. The detection limit is presumed to be in the very low ppb, or sub-ppb, regime and this limit should be obtainable by further optimization of the system.

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