| 1. |
- Andreev, N. E., et al.
(författare)
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Analysis of laser wakefield dynamics in capillary tubes
- 2010
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12
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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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| 2. |
- Aurand, Bastian, et al.
(författare)
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A setup for studies of laser-driven proton acceleration at the Lund Laser Centre
- 2015
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Ingår i: Laser and Particle Beams. - 0263-0346. ; 33:1, s. 59-64
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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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| 3. |
- Batani, D., et al.
(författare)
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Effects of laser prepulse on proton generation
- 2010
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 620:1, s. 76-82
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Konferensbidrag (refereegranskat)abstract
- Low-intensity laser prepulse ( < 10(13) W/cm(2), ns duration) are a major issue in experiments on laser-generation of protons, often limiting the performances of proton sources produced by high-intensity lasers (approximate to 10(19) W/cm(2), ps or fs duration) Several effects are associated to the prepulse and are discussed in this contribution: i) Destruction of thin foil targets by the shock generated by the laser prepulse ii) Creation of preplasma on target front side affecting laser absorption iii) Deformation of target rear side iv) Whole displacement of thin foil targets affecting 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, 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. (C) 2010 Elsevier B.V. All rights reserved.
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| 4. |
- Batani, D., et al.
(författare)
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Effects of laser prepulse on proton generation
- 2010
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Ingår i: Radiation Effects and Defects in Solids. - : Informa UK Limited. - 1042-0150 .- 1029-4953. ; 165:6-10, s. 794-802
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Konferensbidrag (refereegranskat)abstract
- Prepulse is a major issue for laser generation of protons, often limiting the performances of laser sources. Here, we show the use of prepulse (1013W/cm2, ns duration) to actively manipulate the proton beam direction. Under oblique high-intensity irradiation (approximate to 1019W/cm2, ps duration) of the thin foil target, and for low prepulse intensities, the proton beam is directed away from the ounperturbedo target normal. Observations are discussed in terms of target normal sheath acceleration, in combination with a laser-controllable shock locally deforming the target surface.
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| 5. |
- Björklund Svensson, Jonas, et al.
(författare)
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Low-divergence femtosecond X-ray pulses from a passive plasma lens
- 2021
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 17:5, s. 639-645
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Tidskriftsartikel (refereegranskat)abstract
- Electron and X-ray beams originating from compact laser-wakefield accelerators have very small source sizes that are typically on the micrometre scale. Therefore, the beam divergences are relatively high, which makes it difficult to preserve their high quality during transport to applications. To improve on this, tremendous efforts have been invested in controlling the divergence of the electron beams, but no mechanism for generating collimated X-ray beams has yet been demonstrated experimentally. Here we propose and realize a scheme where electron bunches undergoing focusing in a dense, passive plasma lens can emit X-ray pulses with divergences approaching the incoherent limit. Compared with conventional betatron emission, the divergence of this so-called plasma lens radiation is reduced by more than an order of magnitude in solid angle, while maintaining a similar number of emitted photons per electron. This X-ray source offers the possibility of producing brilliant and collimated few-femtosecond X-ray pulses for ultra-fast science, in particular for studies based on X-ray diffraction and absorption spectroscopy. X-ray pulses with low divergences are produced in a laser-wakefield accelerator by focusing electron bunches in a dense passive plasma lens.
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| 6. |
- Burza, Matthias, et al.
(författare)
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Laser wakefield acceleration using wire produced double density ramps
- 2013
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Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- A novel approach to implement and control electron injection into the accelerating phase of a laser wakefield accelerator is presented. It utilizes a wire, which is introduced into the flow of a supersonic gas jet creating shock waves and three regions of differing plasma electron density. If tailored appropriately, the laser plasma interaction takes place in three stages: Laser self-compression, electron injection, and acceleration in the second plasma wave period. Compared to self-injection by wave breaking of a nonlinear plasma wave in a constant density plasma, this scheme increases beam charge by up to 1 order of magnitude in the quasimonoenergetic regime. Electron acceleration in the second plasma wave period reduces electron beam divergence by approximate to 25%, and the localized injection at the density downramps results in spectra with less than a few percent relative spread. DOI: 10.1103/PhysRevSTAB.16.011301
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| 7. |
- Carroll, David C., et al.
(författare)
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Dynamic control and enhancement of laser-accelerated protons using multiple laser pulses
- 2009
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Ingår i: Comptes Rendus. Physique. - : Elsevier BV. - 1631-0705. ; 10:2-3, s. 188-196
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Tidskriftsartikel (refereegranskat)abstract
- The use of schemes involving multiple laser pulses to enhance and control the properties of beams of protons accelerated in ultra-intense laser irradiation of planar foil targets is discussed. Specifically, the schemes include the use of a second laser pulse to produce and control preplasma expansion of the target to enhance energy coupling to the proton beam; the use of a second laser pulse to drive shock deformation of the target to change the direction of the proton beam; and a scheme involving dual high intensity laser pulses to change the properties of the sheath field, with the aim of modifying the proton energy spectrum. An overview of our recent experimental and theoretical results is given. The overall aim of this work is to determine the extent to which the properties of the sheath-accelerated proton beam can be optically controlled, to enable beam delivery at high repetition rates. To cite this article: D.C. Carroll et al., C. R. Physique 10 (2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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| 8. |
- Cassou, K., et al.
(författare)
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Optimization toward a high-average-brightness soft-x-ray laser pumped at grazing incidence
- 2007
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Ingår i: Optics Letters. - 0146-9592. ; 32:2, s. 139-141
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Tidskriftsartikel (refereegranskat)abstract
- We report the near-field imaging characterization of a 10 Hz Ni-like 18.9 nm molybdenum soft-x-ray laser pumped in a grazing incidence pumping (GRIP) geometry with a table-top laser driver. We investigate the effect of varying the GRIP angle on the spatial behavior of the soft-x-ray laser source. After multiparameter optimization, we were able to find conditions to generate routinely a high-repetition-rate soft-x-ray laser with an energy level of up to 3 mu J/pulse and to 6 x 10(17) photons/s/mm(2)/mrad(2)/(0.1% bandwidth) average brightness and 1 x 10(28) photons/s/mm(2)/mrad(2)/(0.1% bandwidth) peak brightness. (c) 2006 Optical Society of America.
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| 9. |
- Desforges, F. G., et al.
(författare)
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Reproducibility of electron beams from laser wakefield acceleration in capillary tubes
- 2014
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 740, s. 54-59
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Tidskriftsartikel (refereegranskat)abstract
- The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside capillary tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter capillary tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.
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| 10. |
- Diego, Guénot, et al.
(författare)
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Simultaneous X-ray absorption and two-photon LIF for imaging the spray formation region
- 2019
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Ingår i: ILASS–Europe 2019, Proceedings of the 29th Conference on Liquid Atomization and Spray Systems, 2-4 September 2019, Paris, France.
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Konferensbidrag (refereegranskat)abstract
- Imaging the spray formation region of atomizing sprays is particularly challenging due to the presence of a variety of irregular liquid structures such as ligaments, liquid blobs, droplets, liquid sheets and a possible liquid core. The number and concentration of those liquid bodies dictate the presence of liquid/air interfaces, which are responsible to undesired scattering effects. The resulting images are blurred, ultimately concealing the real structure of the spray formation region. Due to both, scattering effects and the presence of highly irregular 3D liquid structures, the only reliable measurement of liquid mass in the spray formation region is obtained using X-ray radiography. The generation of collimated X-rays pulsed has been done, in the past, by means of a synchrotron, thus limiting the number of studies that can be performed.In parallel to the use of X-rays, progresses in advanced laser imaging techniques for suppressing multiple scattering issues have been particularly important over the past decade. A very recent solution consists in using 2-photon excitation LIF laser sheet imaging.In this paper, we report for the first time the possibility of simultaneously imaging an atomizing spray using X-ray absorption and 2-photon LIF planar imaging, where the simultaneous single-shot recordings are made over a ~20mmx20mm viewed area. The spray is generated from a commercial fuel port injection system from which, water was injected. The unique illumination/detection scheme proposed here was made possible thanks to the use of X-rays emitted from a laser plasma accelerator (Betatron radiation). For this experiment, we use the High Intensity Laser system at Lund University that provides on target 800mJ, 38fs laser pulses. The emitted X-ray radiation is ranging from 1 to 10keV and peaking at ~2keV. It propagates outside of the vacuum chamber where an X-ray camera records the shadow of the liquid jet. In addition to that, a fraction of the laser pulse ~10mJ is directed on the liquid jet and focuses with a cylindrical lens where it induces fluorescence from a 2-photon excitation process in a dye -here, fluorescein- added to the liquid. The 2p-LIF images provide details on the size and shape of the liquid structures, optically sectioned by the light sheet, while the integrated liquid mass is extracted from the X-ray radiography. This is making the two imaging techniques highly complementary for the characterization of spray systems as well as for further understanding the physics related to liquid atomization.
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