| 31. |
- Ju, J., et al.
(författare)
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Enhancement of x-rays generated by a guided laser wakefield accelerator inside capillary tubes
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:19
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedElectrons accelerated in the nonlinear regime in a laser wakefield accelerator experience transverse oscillations inside the plasma cavity, giving rise to ultra-short pulsed x-rays, also called the betatron radiation. We show that the fluence of x-ray can be enhanced by more than one order of magnitude when the laser is guided by a 10 mm long capillary tube instead of interacting with a 2 mm gas jet. X-rays with a synchrotron-like spectrum and associated critical energy ∼ 5 keV, with a peak brightness of ∼ 1×1021 ph/s/mm2/mrad2/0.1%BW, were achieved by employing 16 TW laser pulses.
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| 32. |
- Ju, J., et al.
(författare)
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Study of electron acceleration and x-ray radiation as a function of plasma density in capillary-guided laser wakefield accelerators
- 2013
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:8
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Tidskriftsartikel (refereegranskat)abstract
- Laser wakefield electron acceleration in the blow-out regime and the associated betatron X-ray radiation were investigated experimentally as a function of the plasma density in a configuration where the laser is guided. Dielectric capillary tubes were employed to assist the laser keeping self-focused over a long distance by collecting the laser energy around its central focal spot. With a 40 fs, 16 TW pulsed laser, electron bunches with tens of pC charge were measured to be accelerated to an energy up to 300 MeV, accompanied by X-ray emission with a peak brightness of the order of 10 21 ph/s/mm(2)/mrad(2)/0.1%BW. Electron trapping and acceleration were studied using the emitted X-ray beam distribution to map the acceleration process; the number of betatron oscillations performed by the electrons was inferred from the correlation between measured X-ray fluence and beam charge. A study of the stability of electron and X-ray generation suggests that the fluctuation of X-ray emission can be reduced by stabilizing the beam charge. The experimental results are in good agreement with 3D particle-in-cell (PIC) simulation. (C) 2013 AIP Publishing LLC.
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| 33. |
- Kazamias, S, et al.
(författare)
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Characterization of a transient collisional Ni-like molybdenum soft x-ray laser pumped in grazing incidence
- 2008
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 77:3
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental results from an extensive investigation of a Ni-like Mo X-ray laser pumped in the transient regime and GRIP configuration (GRazing Incidence Pumping). The pump laser is a 10 Hz, 1 J, Ti:Sa laser system. The main diagnostic is a monochromatic near-field imaging system with a 1.7 micron spatial resolution that shows the soft x-ray laser source size and position relative to the target surface. Changes of those characteristics are observed for different GRIP angles, varied between 15◦ and 21◦, while keeping all other parameters constant. Intense lasing is observed routinely at 18.9 nm with up to 3 microjoule output energy and stable operation is demonstrated at 10 Hz. We have investigated the role of several pumping parameters, in particular the relative energy and delay between the long and short pulse. We show that this multi-parameter scan leads to a well-defined optimal regime of operation and better understanding of the GRIP configuration. Finally, as the GRIP scheme requires careful tailoring of the plasma conditions to the specific soft x-ray laser under investigation, we add a prepulse before the plasma producing long pulse to generate large-scale preplasmas. This increases the brightness of the soft x-ray beam and leads to an almost gaussian near-field spatial profile.
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| 34. |
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| 35. |
- Kovacev, M, et al.
(författare)
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Extreme ultraviolet fourier-transform spectroscopy with high order harmonics
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95:22
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a new scheme for extreme ultraviolet (xuv) Fourier-transform spectroscopy based on the generation of two phase-locked high-harmonic beams. It allows us to measure for the first time interferograms at wavelengths as short as 90 nm, and open the perspective of performing high-resolution Fourier-transform absorption spectroscopy in the xuv. Our measurements also demonstrate that a precise control of the relative phase of harmonic pulses can be obtained with an accuracy on an attosecond time scale, of importance for future xuv pump-xuv probe attosecond spectroscopy.
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| 36. |
- Larsson, Jörgen, et al.
(författare)
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Determination of Radiative Lifetimes In the 3snp(1)p(1) Sequence of Mg-i Using Time-resolved Vuv Laser Spectroscopy
- 1993
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Ingår i: Zeitschrift für Physik D Atoms, Molecules and Clusters. - 0178-7683. ; 27:4, s. 329-331
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Tidskriftsartikel (refereegranskat)abstract
- The radiative lifetimes of the states in the (n=5-8) 3snp P-1(1) sequence of neutral magnesium were investigated using time-resolved laser-induced fluorescence. Excitation from the 3s2 S-1(0), ground state was performed using VUV radiation, which was produced by resonant sum-difference frequency mixing in a krypton gas cell. We find tau(n=5): 54(3) ns, tau(n=6): 140(10) ns, tau(n=7): 290(20) ns, tau(n=8): 475(40) ns. These results were found to be in fair agreement with a Multi Configuration Hartree-Fock (MCHF) calculation.
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| 37. |
- Li, Z. S, et al.
(författare)
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Radiative properties of neutral germanium obtained from excited-state lifetime and branching-ratio measurements and comparison with theoretical calculations
- 1999
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 60:1, s. 198-208
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Tidskriftsartikel (refereegranskat)abstract
- Using time-resolved UV laser-induced fluorescence from a laser-produced plasma, natural radiative lifetimes have been measured for 21 levels of Ge I belonging to the odd-parity 4p4d, 4p5d, and 4p6s configurations. Stimulated Brillouin scattering in water has allowed us to compress Nd:YAG laser pulses pumping a dye laser (where YAG denotes yttrium aluminum garnet), thus yielding 1-ns tunable laser pulses to enable accurate measurements of short lifetimes. Branching ratios of Ge I have been measured by inductively coupled plasma emission spectrometry, the intensity calibration being performed by means of Ar lines emitted by a hollow-cathode lamp. The experimental lifetimes and branching ratios have been combined in order to provide a set of accurate transition probabilities for the 4p-5s and 4p-4d transitions. A relativistic Hartree-Fock; calculation, taking configuration-interaction and polarization effects into account, has been combined with a least-squares optimization procedure of the Slater and spin-orbit integrals in order to test the ability of this approach to correctly predict radiative properties of the group-IV elements. Good agreement between experimental and theoretical transition probability values has been achieved for most of the transitions considered.
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| 38. |
- Lindau, Filip, et al.
(författare)
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Characterization of quasi-monoenergetic electron beams at the lund laser centre
- 2008
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813. ; 36:4, s. 1707-1714
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Tidskriftsartikel (refereegranskat)abstract
- Experiments performed with the high-contrast 0.7-J 35-fs Ti:sapphire laser at the Lund Laser Centre focused into a helium gas jet have produced quasi-monoenergetic electron beams with energies up to 150 MeV. The beam is produced as a result of controlled wavebreaking of a wakefield generated by the relativistically channeled laser beam. Under the best conditions of laser energy and plasma density, a beam with narrow-energy-spread component was produced on every shot with an energy stability of similar to 10% and a pointing stability of similar to 6 mrad. Furthermore, it can be deduced that the electron beam originates from a source with both transverse and longitudinal extents < 10 mu m, implying a pulselength of < 25 fs. These measurements mark an important improvement in the characterization, as well as repeatability, of laser-plasma-generated electron beams with a single driver laser beam.
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| 39. |
- Lindau, Filip, et al.
(författare)
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Laser-accelerated protons with energy dependent beam direction
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95:175002, s. 1-175002
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Tidskriftsartikel (refereegranskat)abstract
- The spatial distribution of protons, accelerated by intense femtosecond laser pulses interacting with thin target foils under oblique irradiation are investigated. Under certain conditions, the proton beams are directed away from the target normal. This deviation is towards the laser forward direction, with an angle that increases with the level and duration of the amplified spontaneous emission pedestal before the main laser pulse. In addition, for a given laser pulse, this beam deviation increases with proton energy. The observations are discussed in terms of different electron acceleration mechanisms and target normal sheath acceleration, in combination with a laser-controllable shock wave locally deforming the target rear surface.
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| 40. |
- Lindau, Filip, et al.
(författare)
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Quantitative study of 10 Hz operation of a soft x-ray laser-energy stability and target considerations
- 2007
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Ingår i: Optics Express. - 1094-4087. ; 15:15, s. 9486-9493
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Tidskriftsartikel (refereegranskat)abstract
- A soft x- ray laser from Ni- like Mo, pumped in grazing incidence ( GRIP), is analyzed with regard to high repetition rate operation. Reliable lasing is obtained, but with significant energy fluctuations attributed mainly to beam pointing jitter from the pump laser. Two modes of operation are compared: continuously moving target and stationary target. With a moving target the soft X- ray output is constant on average, whereas the repeated use of the same target position leads to a pulse energy which increases for several tens of shots. This effect might be caused by improved guiding of the pump laser in the formed groove and the removal, through laser ablation, of the oxide layer on the target surface. (c) 2007 Optical Society of America.
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