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  • 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).
  • 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.
  • 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.
  • 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.
  • 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.
  • Berglund, Martin, et al. (författare)
  • Operation characteristics and optical emission distribution of a miniaturized silicon through-substrate split-ring resonator microplasma source
  • 2014
  • Ingår i: Journal of microelectromechanical systems. - 1057-7157. ; 23:6, s. 1340-1345
  • Tidskriftsartikel (refereegranskat)abstract
    • There are many new microplasma sources being developed for a wide variety of applications, each with different properties tailored to its specific use. Microplasma sources enable portable instruments for, e.g., chemical analysis, sterilization, or activation of substances. A novel microplasma source, based on a microstrip split-ring resonator design with electrodes integrated in its silicon substrate, was designed, manufactured, and evaluated. This device has a plasma discharge gap with a controlled volume and geometry, and offers straightforward integration with other microelectromechancial systems (MEMS) components, e.g., microfluidics. The realized device was resonant at around 2.9 GHz with a quality factor of 18.7. Two different operational modes were observed with the plasma at high pressure being confined in the gap between the electrodes, whereas the plasma at low pressures appeared between the ends of the electrodes on the backside. Measurement of the angular distribution of light emitted from the device with through-substrate electrodes showed narrow emission lobes compared with a reference plasma source with on-substrate electrodes.
  • Bergstrom, H, et al. (författare)
  • Two different types of hollow-cathode discharges used for high resolution laser spectroscopy on copper
  • 1989
  • Ingår i: Zeitschrift Fur Physik D Atoms, Molecules and Clusters. - Springer Berlin / Heidelberg. - 0178-7683. ; 13:3, s. 203-206
  • Tidskriftsartikel (refereegranskat)abstract
    • Two different techniques, Doppler-free saturation spectroscopy on a hollow-cathode discharge and fluorescence spectroscopy on a collimated atomic beam produced from a hollow-cathode discharge, have been used for high-resolution laser-spectroscopy measurements on the 3d10 4p and 5p states in neutral Copper. The relative merits of the two techniques are discussed.
  • Blagoev, KB, et al. (författare)
  • Radiative lifetimes of Zn I, II excited states
  • 2004
  • Ingår i: Physica Scripta. - Royal Swedish Academy of Sciences. - 0031-8949. ; 69:6, s. 433-440
  • Tidskriftsartikel (refereegranskat)abstract
    • Radiative lifetimes of excited states of Zn I (3d(10)4sns S-3(1), n = 6-8; 3d(10) 4snd D-3, n = 4-7) and Zn II (3d(10) 4p P-2(1/2.3/2), 4d D-2(3/2,5/2), 3d(10)5S S-2(1/2)) have been measured using a time-resolved laser-induced fluorescence technique. Single- or two-step excitation of atoms and ions produced by laser ablation was employed. The experimental radiative lifetimes have been compared with theoretical results obtained within a multiconfigurational relativistic Hartree-Fock approach taking core-polarization effects into account.
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