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2.
  • Andreev, N. E., et al. (författare)
  • Analysis of laser wakefield dynamics in capillary tubes
  • 2010
  • Ingår i: New Journal Of Physics. - Iop Publishing. - 1367-2630. ; 12
  • Tidskriftsartikel (refereegranskat)abstract
    • A general approach to the modifications of the spectrum of a laser pulse interacting with matter is elaborated and used for spectral diagnostics of laser wakefield generation in guiding structures. Analytical predictions of the laser frequency red shift due to the wakefield excited in a capillary waveguide are confirmed by self-consistent modeling results. The role of ionization blue shift, and nonlinear laser pulse and wakefield dynamics on the spectrum modification, is analyzed for recent experiments on plasma wave excitation by an intense laser pulse guided in hydrogen-filled glass capillary tubes up to 8 cm long. The dependence of the spectral frequency shift, measured as a function of filling pressure, capillary tube length and incident laser energy, is in excellent agreement with the simulation results, and the associated longitudinal accelerating field is in the range 1-10 GV m(-1).
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3.
  • Aurand, Bastian, et al. (författare)
  • A setup for studies of laser-driven proton acceleration at the Lund Laser Centre
  • 2015
  • Ingår i: Laser and Particle Beams. - Cambridge Univ Press. - 0263-0346. ; 33:1, s. 59-64
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on a setup for the investigation of proton acceleration in the regime of target normal sheath acceleration. The main interest here is to focus on stable laser beam parameters as well as a reliable target setup and diagnostics in order to do extensive and systematic studies on the acceleration mechanism. A motorized target alignment system in combination with large target mounts allows for up to 340 shots with high repetition rate without breaking the vacuum. This performance is used to conduct experiments with a split mirror setup exploring the effect of spatial and temporal separation between the pulses on the acceleration mechanism and on the resulting proton beam.
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4.
  • Axelsson, Karin, 1968-, et al. (författare)
  • Communication Analysis of Public Forms
  • 2007
  • Ingår i: International Journal of Public Information Systems. - Sundsvall : MidSweden University. ; :3, s. 161-181
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper adopts a communication perspective on forms in public e-services. This perspective emphasizes that the main purpose of such forms is to facilitate communication between citizens and government agencies. The form is perceived as a tool for performing communicative actions. A communication analysis (CA) method, originally developed for systems requirements engineering, is applied on a public form; i.e. the medical certificate used in connection with a citizen’s application for a provisional driving license in Sweden. The CA method consists of a set of questions related tothree communicative categories; conditions, actions, and consequences. The CA method is used in order to explore the communicative roles of forms in public e-services. As a result of the communication analysis four multi-functional purposes of citizen and government agency communication are discovered. These purposes contribute to the understanding and evaluation of forms in public e-services. The communicative roles, and their multi-functional purposes, are important design features to focus in the development of e-services and electronic forms. Besides these findings, another outcomeis that the CA method has been tested in an e-government context. The communication perspective, as well as the CA method, contribute with useful insights in this context.
5.
  • Baklanov, A. V, et al. (författare)
  • Nanosecond and femtosecond probing of the dynamics of the UV-photodissociation of perfluoroethyliodide C2F5I
  • 2001
  • Ingår i: Journal of Chemical Physics. - 0021-9606. ; 115:24, s. 11157-11165
  • Tidskriftsartikel (refereegranskat)abstract
    • The ns photodissociation of perfluoroethyliodide C2F5I at 266 nm has been studied by using the resonant two-photon ionization (R2PI) technique. Recoil anisotropy parameters as well as average translational energy of the I atoms in the fine structure states P-2(1/2) and P-2(3/2) have been determined. The main contribution (99%) to the absorption at 266 nm was found to be caused by a parallel transition to the (3)Q(0) state which gives mainly excited-state atoms I(P-2(1/2)). The ground-state atoms I(P-2(3/2)) were found to appear mainly (88%) from the primarily excited (3)Q(0) state via curve-crossing (3)Q(0)-(1)Q(1) and to a lesser extent (12%) from direct absorption by a perpendicular transition to the (1)Q(1) and (3)Q(1) states. The fs pump-dump technique in combination with ns R2PI probing of the fragments I(P-2(1/2)) and I(P-2(3/2)) and time-of-flight mass spectrometry have been applied to probe the early stage dynamics of the C2F5I molecule on the excited state (3)Q(0) potential energy surface (PES). The evolution time of the excited molecule to the point where the energy gap between the excited state (3)Q(0) and the ground-state potential energy surfaces drops to a value of about 12 440 cm-1 was found to be 52 +/- 13 fs. This time corresponds to about 0.8 Angstrom extension of the C-I bond distance. The molecular dynamics simulation with DFT calculated ground-state PES and (3)Q(0) PES with the shape calculated for methyl iodide found in the literature gives reasonable agreement with the experimental result for the evolution time. (C) 2001 American Institute of Physics.
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6.
  • Batani, D., et al. (författare)
  • Effects of laser prepulses on laser-induced proton generation
  • 2010
  • Ingår i: New Journal Of Physics. - Iop Publishing. - 1367-2630. ; 12
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-intensity laser prepulses (<10(13) W cm(-2), nanosecond duration) are a major issue in experiments on laser-induced generation of protons, often limiting the performances of proton sources produced by high-intensity lasers (approximate to 10(19) W cm(-2), picosecond or femtosecond duration). Depending on the intensity regime, several effects may be associated with the prepulse, some of which are discussed in this paper: (i) destruction of thin foil targets by the shock generated by the laser prepulse; (ii) creation of preplasma on the target front side affecting laser absorption; (iii) deformation of the target rear side; and (iv) whole displacement of thin foil targets affecting the focusing condition. In particular, we show that under oblique high-intensity irradiation and for low prepulse intensities, the proton beam is directed away from the target normal. Deviation is towards the laser forward direction, with an angle that increases with the level and duration of the ASE pedestal. Also, for a given laser pulse, the beam deviation increases with proton energy. The observations are discussed in terms of target normal sheath acceleration, in combination with a laser-controllable shock wave locally deforming the target surface.
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7.
  • Berglund, Martin, 1985-, et al. (författare)
  • Evaluation of a microplasma source based on a stripline split-ring resonator
  • 2013
  • Ingår i: Plasma sources science & technology (Print). - Institute of Physics (IOP). - 0963-0252. ; 22:5, s. 055017
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, a stripline split-ring resonator microwave-induced plasma source, aimed for integration in complex systems, is presented and compared with a traditional microstrip design. Devices based on the two designs are evaluated using a plasma breakdown test setup for measuring the power required to ignite plasmas at different pressures. Moreover, the radiation efficiency of the devices is investigated with a Wheeler cap, and their electromagnetic compatibility is investigated in a variable electrical environment emulating an application. Finally, the basic properties of the plasma in the two designs are investigated in terms of electron temperature, plasma potential and ion density. The study shows that, with a minor increase in plasma ignition power, the stripline design provides a more isolated and easy-to-integrate alternative to the conventional microstrip design. Moreover, the stripline devices showed a decreased antenna efficiency as compared with their microstrip counterparts, which is beneficial for plasma sources. Furthermore, the investigated stripline devices exhibited virtually no frequency shift in a varying electromagnetic environment, whereas the resonance frequency of their microstrip counterparts shifted up to 17.5%. With regard to the plasma parameters, the different designs showed only minor differences in electron temperature, whereas the ion density was higher with the stripline design.
8.
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9.
  • Berglund, Martin, 1985-, et al. (författare)
  • Manufacturing Miniature Langmuir probes by Fusing Platinum Bond Wires
  • ????
  • Ingår i: Journal of Micromechanics and Microengineering. - 0960-1317.
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper reports on a novel method for manufacturing microscopic Langmuir probes with spherical tips from platinum bond wires for plasma characterization in microplasma sources by fusing. Here, the resulting endpoints, formed by droplets of a fused wire, are intended to act as a spherical Langmuir probe. For studying the fusing behavior, bond wires were wedge-bonded over a 2 mm wide slit, to emulate the final application, and fused at different currents and voltages. For electrical isolation, a set of wires were coated with a 4 µm thick layer of Parylene before they were fused. After fusing, the gap size, as well as the shape and area of the ends of the remaining stubs were measured. The yield of the process was also investigated, and the fusing event was studied using a high-speed camera for analyzing the dynamics of fusing. Four characteristic tip shapes were observed: spherical, semi-spherical, serpentine shaped and folded. The stub length leveled out at ~420µm. The fusing of the coated wires required a higher power for attaining a spherical shape. Finally, a Parylene coated bond wire was integrated into a stripline split-ring resonator (SSRR) microplasma source, and fused to form two Langmuir probes with spherical endpoints. These probes were used for measuring the I-V characteristics of a plasma generated by the SSRR. In a voltage range between -60 V and 60 V, the fused stubs exhibited the expected behavior of spherical Langmuir probes and will be considered for future integration.
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10.
  • Berglund, Martin, 1985-, et al. (författare)
  • Microplasma source for optogalvanic spectroscopy of nanogram samples
  • 2013
  • Ingår i: Journal of Applied Physics. - American Institute of Physics (AIP). - 0021-8979. ; 114:3, s. 033302
  • Tidskriftsartikel (refereegranskat)abstract
    • The demand for analysis of smaller samples in isotopic ratio measurements of rare isotopes is continuously rising with the development of new applications, particularly in biomedicine. Interesting in this aspect are methods based on optogalvanic spectroscopy, which have been reported to facilitate both 13C-to-12C and 14C-to-12C ratio measurements with high sensitivity. These methods also facilitate analysis of very small samples, down to the microgram range, which makes them very competitive to other technologies, e.g., accelerator mass spectroscopy. However, there exists a demand for moving beyond the microgram range, especially from regenerative medicine, where samples consist of, e.g., DNA, and, hence, the total sample amount is extremely small. Making optogalvanic spectroscopy of carbon isotopes applicable to such small samples, requires miniaturization of the key component of the system, namely the plasma source, in which the sample is ionized before analysis. In this paper, a novel design of such a microplasma source based on a stripline split-ring resonator is presented and evaluated in a basic optogalvanic spectrometer. The investigations focus on the capability of the plasma source to measure the optogalvanic signal in general, and the effect of different system and device specific parameters on the amplitude and stability of the optogalvanic signal in particular. Different sources of noise and instabilities are identified, and methods of mitigating these issues are discussed. Finally, the ability of the cell to handle analysis of samples down to the nanogram range is investigated, pinpointing the great prospects of stripline split-ring resonators in optogalvanic spectroscopy.
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