| 1. |
- Aurand, B., et al.
(författare)
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Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution
- 2016
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on a study of the spatial profile of proton beams produced through target normal sheath acceleration using flat target foils and changing the laser intensity distribution on the target front surface. This is done by either defocusing a single laser pulse or by using a split-pulse setup and irradiating the target with two identical laser pulses with variable spatial separation. The resulting proton beam profile and the energy spectrum are recorded as functions of the focal spot size of the single laser pulse and of the separation between the two pulses. A shaping of the resulting proton beam profile, related to both an increase in flux of low-energy protons in the target normal direction and a decrease in their divergence, in one or two dimensions, is observed. The results are explained by simple modelling of rear surface sheath field expansion, ionization, and projection of the resulting proton beam.
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| 2. |
- Bhadoria, Shikha, 1991, et al.
(författare)
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Mapping the power-law decay of high-harmonic spectra from few-cycle laser-solid interactions
- 2022
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 29
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Tidskriftsartikel (refereegranskat)abstract
- Visible or near infrared light can be manipulated to produce bursts of coherent extreme ultraviolet or x rays via the relativistic high-order harmonic generation process when a laser irradiates a solid plasma target. The intensity of the spectral components of the reflected signal decays with the increase in harmonic order and the efficiency of this non-linear process largely hinges on how prompt this decay is. This is governed by the conditions of the laser-plasma interaction for which various models have been proposed. At relativistic intensities, a spectrum exhibiting a power-law decay with an exponent of 8/3 or 4/3 is often stated. Here, we analyze the dependence of this exponent on interaction parameters, including the angle of incidence, the carrier envelope phase, intensity of the laser, and the pre-plasma length, and discuss opportunities for optimization. Our simulations show that, rather than there being one universal exponent, the spectral decay is a continuous function of the laser-plasma interaction parameters.
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| 3. |
- Blanco, M., et al.
(författare)
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Controlling the ellipticity of attosecond pulses produced by laser irradiation of overdense plasmas
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:9
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of high-intensity laser pulses and solid targets provides a promising way to create compact, tunable, and bright XUV attosecond sources that can become a unique tool for a variety of applications. However, it is important to control the polarization state of this XUV radiation and to do so in the most efficient regime of generation. Using the relativistic electronic spring (RES) model and particle-in-cell simulations, we show that the polarization state of the generated attosecond pulses can be tuned in a wide range of parameters by adjusting the polarization and/or the angle of incidence of the laser radiation. In particular, we demonstrate the possibility of producing circularly polarized attosecond pulses in a wide variety of setups.
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| 4. |
- Gonoskov, Arkady, 1984
(författare)
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Theory of relativistic radiation reflection from plasmas
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:1
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Tidskriftsartikel (refereegranskat)abstract
- We consider the reflection of relativistically strong radiation from plasma and identify the physical origin of the electrons' tendency to form a thin sheet, which maintains its localisation throughout its motion. Thereby, we justify the principle of relativistic electronic spring (RES) proposed in [Gonoskov et al., Phys. Rev. E 84, 046403 (2011)]. Using the RES principle, we derive a closed set of differential equations that describe the reflection of radiation with arbitrary variation of polarization and intensity from plasma with an arbitrary density profile for an arbitrary angle of incidence. We confirm with ab initio PIC simulations that the developed theory accurately describes laser-plasma interactions in the regime where the reflection of relativistically strong radiation is accompanied by significant, repeated relocation of plasma electrons. In particular, the theory can be applied for the studies of plasma heating and coherent and incoherent emissions in the RES regime of high-intensity laser-plasma interaction.
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| 5. |
- Magnusson, Joel, 1991, et al.
(författare)
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Prospects for laser-driven ion acceleration through controlled displacement of electrons by standing waves
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:5
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Tidskriftsartikel (refereegranskat)abstract
- During the interaction of intense femtosecond laser pulses with various targets, the natural mechanisms of laser energy transformation inherently lack temporal control and thus commonly do not provide opportunities for a controlled generation of a well-collimated, high-charge beam of ions with a given energy of particular interest. In an effort to alleviate this problem, it was recently proposed that the ions can be dragged by an electron bunch trapped in a controllably moving potential well formed by laser radiation. Such standing-wave acceleration (SWA) can be achieved through reflection of a chirped laser pulse from a mirror, which has been formulated as the concept of chirped-standing-wave acceleration (CSWA). Here, we analyse general feasibility aspects of the SWA approach and demonstrate its reasonable robustness against field structure imperfections, such as those caused by misalignment, ellipticity, and limited contrast. Using this, we also identify prospects and limitations of the CSWA concept.
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| 6. |
- Svedung Wettervik, Benjamin, 1990, et al.
(författare)
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Physics of the laser-plasma interface in the relativistic regime of interaction
- 2019
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 26:5
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Tidskriftsartikel (refereegranskat)abstract
- The reflection of intense laser radiation from solids appears as a result of relativistic dynamics of the electrons driven by both incoming and self-generated electromagnetic fields at the periphery of the emerging dense plasma. In the case of highly relativistic motion, electrons tend to form a thin oscillating layer, which makes it possible to model the interaction and obtain the temporal structure of the reflected radiation. The modeling reveals the possibility and conditions for producing singularly intense and short extreme ultraviolet (XUV) bursts of radiation, which are interesting for many applications. However, the intensity and duration of the XUV bursts, as well as the high-energy end of the harmonic spectrum, depend on the thickness of the layer and its internal structure which are not assessed by such macroscopic modeling. Here, we analyze the microscopic physics of this layer and clarify how its parameters are bound and how this controls the outlined properties of XUV bursts.
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| 7. |
- Svedung Wettervik, Benjamin, 1990, et al.
(författare)
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Prospects and limitations of wakefield acceleration in solids
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:1
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Tidskriftsartikel (refereegranskat)abstract
- Advances in the generation of relativistic intensity pulses with wavelengths in the X-ray regime, through high harmonic generation from near-critical plasmas, open up the possibility of X-ray driven wakefield acceleration. The similarity scaling laws for laser plasma interaction suggest that X-rays can drive wakefields in solid materials providing TeV/cm gradients, resulting in electron and photon beams of extremely short duration. However, the wavelength reduction enhances the quantum parameter χ, hence opening the question of the role of non-scalable physics, e.g., the effects of radiation reaction. Using three dimensional Particle-In-Cell simulations incorporating QED effects, we show that for the wavelength λ=5 nm and relativistic amplitudes a0=10-100, similarity scaling holds to a high degree, combined with χ∼1 operation already at moderate a0∼50, leading to photon emissions with energies comparable to the electron energies. Contrasting to the generation of photons with high energies, the reduced frequency of photon emission at X-ray wavelengths (compared with that at optical wavelengths) leads to a reduction in the amount of energy that is removed from the electron population through radiation reaction. Furthermore, as the emission frequency approaches the laser frequency, the importance of radiation reaction trapping as a depletion mechanism is reduced, compared with that at optical wavelengths for a 0 leading to similar χ.
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| 8. |
- Svensson, K., et al.
(författare)
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Transverse expansion of the electron sheath during laser acceleration of protons
- 2017
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 24:12
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Tidskriftsartikel (refereegranskat)abstract
- The transverse expansion of the electrostatic sheath during target normal sheath acceleration of protons is investigated experimentally using a setup with two synchronized laser pulses. With the pulses spatially separated by less than three laser spot diameters, the resulting proton beam profiles become elliptical. By introducing a small intensity difference between the two pulses, the ellipses are rotated by a certain angle, except if the spatial separation of the two laser pulses is in the plane of incidence. The rotation angle is shown to depend on the relative intensity of the two pulses. The observed effects are found to require high temporal contrasts of the laser pulses. A simple model describing how the transverse shape of the electron sheath on the rear of the target depends on the relative intensity between the foci is presented. The model assumptions are verified, and the unknown dependence of the transverse extents of the sheaths are estimated self-consistently through a series of high resolution, two-dimensional particle-in-cell simulations. The results predicted by the model are also shown to be consistent with those obtained from the experiment.
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| 9. |
- Wallstén Wallin, Erik Karl, 1986, et al.
(författare)
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Effects of high energy photon emissions in laser generated ultra-relativistic plasmas: Real-time synchrotron simulations
- 2015
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 22:3
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Tidskriftsartikel (refereegranskat)abstract
- We model the emission of high energy photons due to relativistic charged particle motion in intense laser-plasma interactions. This is done within a particle-in-cell code, for which high frequency radiation normally cannot be resolved due to finite time steps and grid size. A simple expression for the synchrotron radiation spectra is used together with a Monte-Carlo method for the emittance. We extend previous work by allowing for arbitrary fields, considering the particles to be in instantaneous circular motion due to an effective magnetic field. Furthermore, we implement noise reduction techniques and present validity estimates of the method. Finally, we perform a rigorous comparison to the mechanism of radiation reaction, and find the emitted energy to be in excellent agreement with the losses calculated using radiation reaction.
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| 10. |
- Wallstén Wallin, Erik Karl, 1986, et al.
(författare)
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Radiation emission from braided electrons in interacting wakefields
- 2017
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 24:9
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Tidskriftsartikel (refereegranskat)abstract
- The radiation emission from electrons wiggling in a laser wakefield acceleration (LWFA) process, being initially considered as a parasitic effect for the electron energy gain, can eventually serve as a novel X-ray source, which could be used for diagnostic purposes. Although several schemes for enhancing the X-ray emission in LWFA has been recently proposed and analyzed, finding an efficient way to use and control this radiation emission remains an important problem. Based on analytical estimates and 3D particle-in-cell simulations, we here propose and examine a new method utilizing two colliding LWFA patterns with an angle in between their propagation directions. Varying the angle of collision, the distance of acceleration before the collision and other parameters provide an unprecedented control over the emission parameters. Moreover, we reveal here that for a collision angle of 5°, the two wakefields merge into a single LWFA cavity, inducing strong and stable collective oscillations between the two trapped electron bunches. This results in an X-ray emission which is strongly peaked, both in the spatial and frequency domains. The basic concept of the proposed scheme may pave a way for using LWFA radiation sources in many important applications, such as phase-contrast radiography.
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