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Sökning: WFRF:(Wahlström Claes Göran)

  • Resultat 141-150 av 157
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141.
  • Svanberg, Sune, et al. (författare)
  • Lund High-power Laser Facility - Systems and 1st Results
  • 1994
  • Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 49:2, s. 187-197
  • Tidskriftsartikel (refereegranskat)abstract
    • A high-power laser facility has been established at the Lund Institute of Technology, Sweden, available to national groups and their international collaboration partners. The laboratory incorporates three major 10 Hz laser systems, that can be operated individually or synchronized in combined use. Each system represents extreme optical powers in a certain sense. The main system is a terawatt laser based on chirped pulse amplification in titanium doped sapphire. It generates radiation tunable in the 760-840 nm region with a maximum power of 1.5TW in 150 fs long pulses. A further system is set up to generate nanosecond pulses of extremely bright VUV radiation (down to 120 nm) by sum-difference four-wave mixing in krypton gas. Finally, a third system generates widely tunable radiation (200-900 nm) of a pulse duration of 10's of picoseconds. The experimental areas incorporate target chambers, spectrometers and fast electronics. The systems have been used in a number of experiments requiring high optical powers, and a brief account of the initial activities is given. Detailed studies of high-harmonic generation in inert gases are reported as well as the generation and application of hard X-rays from microplasmas. Intense white-light generation by self-phase modulation in water has been used for biological tissue studies and for chemical pump/probe experiments. VUV radiation has been used for studies of radiative properties of excited states of free atoms. Finally, the picosecond laser system has been utilized in studies of the temporal structure of harmonics from an inert gas and for soft X-ray generation for high-resolution microscopy. A discussion section concludes the presentation.
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142.
  • Tillman, C, et al. (författare)
  • Imaging Using Hard X-rays From A Laser-produced Plasma
  • 1995
  • Ingår i: Applied Physics B. - 0946-2171. ; 61:4, s. 333-338
  • Tidskriftsartikel (refereegranskat)abstract
    • Imaging of technical and biological objects using hard X-rays from a laser-produced plasma source is demonstrated. Magnification radiography and single-shot imaging of biological samples are feasible with the source, which utilised focused radiation from a short-pulse terawatt laser. Differential imaging with element specificity and a new projection geometry for X-ray radiography are proposed.
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143.
  • Ubachs, W, et al. (författare)
  • Lifetime measurements on the c '(1)(4)Sigma(+)(u), v=0, 1 and 2 states of molecular nitrogen
  • 2001
  • Ingår i: Chemical Physics. - 0301-0104. ; 270:1, s. 215-225
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited state lifetimes of c(4)('1)Sigma (+)(u), upsilon = 0-2 states of molecular nitrogen have been determined in a laboratory investigation using a picosecond XUV laser in a pump-probe configuration. For c(4)('1)Sigma (+)(u) upsilon = 0 the lifetime is tau = 740 +/- 50 ps, for the lowest rotational states. For higher rotational states a gradual shift towards tau = 495 ps is found in agreement with previous findings that these states are subject to predissociation. For c(4)(') Sigma (+)(u) upsilon = 1 no J-dependence is found and values for two isotopomers are reported: tau = 240 ps for (NN)-N-14-N-15 = 240 ps for (NN)-N-14-N-15. For c(4)('1)Sigma (+)(u) upsilon = 2 a lifetime for the lowest rotational states (J = 0-3) was derived: tau = 675 +/- 50 ps; for J = 11 a lifetime of tau less than or equal to 120 ps is deduced. All values for the lifetimes including the J-dependences are explained in a model based on Rydberg-valence interaction. (C) 2001 Elsevier Science B.V. All rights reserved.
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144.
  • Uhlig, Jens, et al. (författare)
  • Laser generated 300 keV electron beams from water
  • 2011
  • Ingår i: Laser and Particle Beams. - 0263-0346. ; 29:4, s. 415-424
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract in Undetermined300 keV electron beams with energy peaked in the range 280–390 keV were generated by focusing a high contrast ratio but temporally double pulsed 800 nm ultrafast laser onto a flowing water jet under both helium atmosphere at ambient pressure and water aspirator vacuum conditions, using laser intensities in the range 1015–1018 Wcm−2. Their characteristics have been investigated as functions of inter-pulse delay, incidence geometry and laser pulse chirp. Shot-to-shot variation of the beams' equatorial and azimuthal distributions was also recorded in real time. Measurements of the emitted charge and energy have been performed. Secondary X-ray emission arising from impingement of the electron beams on the target chamber walls and other parts of the apparatus have been identified. Preliminary results after transition to a high repetition rate laser system have shown similar behavior. Approaches for improvements and applications are suggested.
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145.
  • Vallières, Simon, et al. (författare)
  • Enhanced laser-driven proton acceleration using nanowire targets
  • 2021
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser-driven proton acceleration is a growing field of interest in the high-power laser community. One of the big challenges related to the most routinely used laser-driven ion acceleration mechanism, Target-Normal Sheath Acceleration (TNSA), is to enhance the laser-to-proton energy transfer such as to maximize the proton kinetic energy and number. A way to achieve this is using nanostructured target surfaces in the laser-matter interaction. In this paper, we show that nanowire structures can increase the maximum proton energy by a factor of two, triple the proton temperature and boost the proton numbers, in a campaign performed on the ultra-high contrast 10 TW laser at the Lund Laser Center (LLC). The optimal nanowire length, generating maximum proton energies around 6 MeV, is around 1–2 μm. This nanowire length is sufficient to form well-defined highly-absorptive NW forests and short enough to minimize the energy loss of hot electrons going through the target bulk. Results are further supported by Particle-In-Cell simulations. Systematically analyzing nanowire length, diameter and gap size, we examine the underlying physical mechanisms that are provoking the enhancement of the longitudinal accelerating electric field. The parameter scan analysis shows that optimizing the spatial gap between the nanowires leads to larger enhancement than by the nanowire diameter and length, through increased electron heating.
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146.
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147.
  • Wahlström, Claes-Göran, et al. (författare)
  • High-order harmonic generation
  • 1995
  • Ingår i: The 4th International Colloquium: X-ray Lasers 1994. - : AIP. ; 332:1, s. 312-319
  • Konferensbidrag (refereegranskat)
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148.
  • Wahlström, Claes-Göran, et al. (författare)
  • High-order Harmonic-generation In Rare-gases With An Intense Short-pulse Laser
  • 1993
  • Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 48:6, s. 4709-4720
  • Tidskriftsartikel (refereegranskat)abstract
    • We present experimental studies of high-order harmonic generation in the rare gases performed with a short-pulse titanium sapphire laser operating at 794 nm in the 10(14)-10(15) W/cm2 range. The harmonic yields generated in neon and in argon are studied for all orders as a function of the laser intensity. They vary first rather steeply, in the cutoff region, then much more slowly in the plateau region, and, finally, they saturate when the medium gets ionized. The dependence of the high-order harmonic cutoff with the laser intensity in neon and argon is found to be lower than that predicted in single-atom theories. We observe high-order harmonics in argon and xenon (up to the 65th and 45th, respectively) at 10(15) W/cm2, which we attribute to harmonic generation from ions. We also show how the harmonic and fundamental spectra get blueshifted when the medium becomes ionized.
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149.
  • Wahlström, Claes-Göran (författare)
  • High-order Harmonic-generation Using High-power Lasers
  • 1994
  • Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 49:2, s. 201-208
  • Tidskriftsartikel (refereegranskat)abstract
    • An introduction to high-power lasers and strong-field laser-atom interactions is given, and the main experimental and theoretical results concerning high-order harmonic generation are reviewed. The single atom response as well as the macroscopic phase-matching effect is discussed. The formation and extent of the characteristic plateau in the harmonic spectra are discussed in terms of a physical picture valid in the tunnel-ionisation regime. Very high-order harmonics have been reported, opening the way to construct bright sources of coherent radiation in the XUV and soft X-ray ranges. Some examples of possible applications of such a source are presented.
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150.
  • Wahlström, Claes-Göran, et al. (författare)
  • Supersonic jets of hydrogen and helium for laser wakefield acceleration
  • 2016
  • Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 19
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of laser wakefield accelerated electrons in supersonic gas flows of hydrogen and helium are investigated. At identical backing pressure, we find that electron beams emerging from helium show large variations in their spectral and spatial distributions, whereas electron beams accelerated in hydrogen plasmas show a higher degree of reproducibility. In an experimental investigation of the relation between neutral gas density and backing pressure, it is found that the resulting number density for helium is ∼30% higher than for hydrogen at the same backing pressure. The observed differences in electron beam properties between the two gases can thus be explained by differences in plasma electron density. This interpretation is verified by repeating the laser wakefield acceleration experiment using similar plasma electron densities for the two gases, which then yielded electron beams with similar properties.
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  • Resultat 141-150 av 157
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