The energy spread in laser wakefield accelerators is primarily limited by the energy chirp introduced during the injection and acceleration processes. Here, we propose the use of longitudinal density ...tailoring to reduce the beam chirp at the end of the accelerator. Experimental data sustained by quasi-3D particle-in-cell simulations show that broadband electron beams can be converted to quasimonoenergetic beams of ≤10% energy spread while maintaining a high charge of more than 120 pC. In the linear and quasilinear regimes of wakefield acceleration, the method could provide even lower, subpercent level, energy spread.
Ionization injection is a simple and efficient method to trap an electron beam in a laser plasma accelerator. Yet, because of a long injection length, this injection technique leads generally to the ...production of large energy spread electron beams. Here, we propose to use a shock front transition to localize the injection. Experimental results show that the energy spread can be reduced down to 10 MeV and that the beam energy can be tuned by varying the position of the shock. This simple technique leads to very stable and reliable injection even for modest laser energy. It should therefore become a unique tool for the development of laser-plasma accelerators.
The achievable energy and the stability of accelerated electron beams have been the most critical issues in laser wakefield acceleration. As laser propagation, plasma wave formation and electron ...acceleration are highly nonlinear processes, the laser wakefield acceleration (LWFA) is extremely sensitive to initial experimental conditions. We propose a simple and elegant waveform control method for the LWFA process to enhance the performance of a laser electron accelerator by applying a fully optical and programmable technique to control the chirp of PW laser pulses. We found sensitive dependence of energy and stability of electron beams on the spectral phase of laser pulses and obtained stable 2-GeV electron beams from a 1-cm gas cell of helium. The waveform control technique for LWFA would prompt practical applications of centimeter-scale GeV-electron accelerators to a compact radiation sources in the x-ray and γ-ray regions.
Recent progress in laser-driven plasma acceleration now enables the acceleration of electrons to several gigaelectronvolts. Taking advantage of these novel accelerators, ultrashort, compact, and ...spatially coherent x-ray sources called betatron radiation have been developed and applied to high-resolution imaging. However, the scope of the betatron sources is limited by a low energy efficiency and a photon energy in the 10 s of kiloelectronvolt range, which for example prohibits the use of these sources for probing dense matter. Here, based on three-dimensional particle-in-cell simulations, we propose an original hybrid scheme that combines a low-density laser-driven plasma accelerator with a high-density beam-driven plasma radiator, thereby considerably increasing the photon energy and the radiated energy of the betatron source. The energy efficiency is also greatly improved, with about 1% of the laser energy transferred to the radiation, and the γ-ray photon energy exceeds the megaelectronvolt range when using a 15 J laser pulse. This high-brilliance hybrid betatron source opens the way to a wide range of applications requiring MeV photons, such as the production of medical isotopes with photonuclear reactions, radiography of dense objects in the defense or industrial domains, and imaging in nuclear physics.
Laser-plasma technology promises a drastic reduction of the size of high-energy electron accelerators. It could make free-electron lasers available to a broad scientific community and push further ...the limits of electron accelerators for high-energy physics. Furthermore, the unique femtosecond nature of the source makes it a promising tool for the study of ultrafast phenomena. However, applications are hindered by the lack of suitable lens to transport this kind of high-current electron beams mainly due to their divergence. Here we show that this issue can be solved by using a laser-plasma lens in which the field gradients are five order of magnitude larger than in conventional optics. We demonstrate a reduction of the divergence by nearly a factor of three, which should allow for an efficient coupling of the beam with a conventional beam transport line.
The quality of laser wakefield accelerated electrons beams is strongly determined by the physical mechanism exploited to inject electrons in the wakefield. One of the techniques used to improve the ...beam quality is the density transition injection, where the electron trapping occurs as the laser pulse passes a sharp density transition created in the plasma. Although this technique has been widely demonstrated experimentally, the literature lacks theoretical and numerical studies on the effects of all the transition parameters. We thus report and discuss the results of a series of particle in cell (PIC) simulations where the density transition height and downramp length are systematically varied, to show how the electron beam parameters and the injection mechanism are affected by the density transition parameters.
As a high-intensity laser-pulse reflects on a plasma mirror, high-order harmonics of the incident frequency can be generated in the reflected beam. We present a numerical study of the phase ...properties of these individual harmonics, and demonstrate experimentally that they can be coherently controlled through the phase of the driving laser field. The harmonic intrinsic phase, resulting from the generation process, is directly related to the coherent sub-laser-cycle dynamics of plasma electrons, and thus constitutes a new experimental probe of these dynamics.
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