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One of the major goals of research for laser-plasma accelerators is the realization of compact sources of femtosecond X-rays. In particular, using the modest electron energies obtained with existing laser systems, Compton scattering a photon beam off a relativistic electron bunch has been proposed as a source of high-energy and high-brightness photons. However, laser-plasma based approaches to Compton scattering have not, to date, produced X-rays above 1 keV. Here, we present a simple and compact scheme for a Compton source based on the combination of a laser-plasma accelerator and a plasma mirror. This approach is used to produce a broadband spectrum of X-rays extending up to hundreds of keV and with a 10,000-fold increase in brightness over Compton X-ray sources based on conventional accelerators. We anticipate that this technique will lead to compact, high-repetition-rate sources of ultrafast (femtosecond), tunable (X- through gamma-ray) and low-divergence (~1 degree) photons from source sizes on the order of a micrometre.
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A scheme for fast, compact, and controllable acceleration of heavy particles in vacuum has been recently proposed [F. Peano et al., New J. Phys. 10 033028 (2008)], wherein two counterpropagating laser beams with variable frequencies drive a beat-wave structure with variable phase velocity, leading to particle trapping and acceleration. The technique allows for fine control over the energy distribution and the total charge of the accelerated beam, to be obtained via tuning of the frequency variation. Here, the theoretical bases of the acceleration scheme are described, and the possibility of applications to ultrafast muon acceleration and to the prompt extraction of cold-muon beams is discussed.
A scheme for fast, compact, and controllable acceleration of heavy particles in vacuum is proposed, in which two counterpropagating lasers with variable frequencies drive a beat-wave structure with variable phase velocity, thus allowing for trapping and acceleration of heavy particles, such as ions or muons. Fine control over the energy distribution and the total charge of the beam is obtained via tuning of the frequency variation. The acceleration scheme is described with a one-dimensional theory, providing the general conditions for trapping and scaling laws for the relevant features of the particle beam. Two-dimensional, electromagnetic particle-in-cell simulations confirm the validity and the robustness of the physical mechanism.
We calculate the differential cross sections for Compton scattering of photons described by Hermite Gaussian (HG) wave function in the framework of relativistic quantum mechanics. The HG wave gamma-rays propagating along the z-direction have quantum numbers of nodes of nx and ny in the x- and y-directions, respectively. The calculated differential cross section is symmetric with respect to both the zx- and zy-planes. The nodes whose number is identical with nx and ny appear in the energy spectrum measured in zx- and zy-planes, respectively. These results indicate that it is possible to identify the HG wave photon and its quantum numbers nx and ny by measuring Compton scattering. The present proposed method can be also applied to gamma-ray astronomy.
Injection of well-defined, high-quality electron populations into plasma waves is a key challenge of plasma wakefield accelerators. Here, we report on the first experimental demonstration of plasma density downramp injection in an electron-driven plasma wakefield accelerator, which can be controlled and tuned in all-optical fashion by mJ-level laser pulses. The laser pulse is directed across the path of the plasma wave before its arrival, where it generates a local plasma density spike in addition to the background plasma by tunnelling ionization of a high ionization threshold gas component. This density spike distorts the plasma wave during the density downramp, causing plasma electrons to be injected into the plasma wave. By tuning the laser pulse energy and shape, highly flexible plasma density spike profiles can be designed, enabling dark current free, versatile production of high-quality electron beams. This in turn permits creation of unique injected beam configurations such as counter-oscillating twin beamlets.
Laser-plasma accelerators produce electric fields of the order of 100 GV/m, more than 1000 times larger than radio-frequency accelerators. Thanks to this unique field strength, they appear as a promising path to generate electron beams beyond the TeV, for high-energy physics. Yet, large electric fields are of little benefit if they are not maintained over a long distance. It is therefore of the utmost importance to guide the ultra-intense laser pulse that drives the accelerator. Reaching very high energies is equally useless if the properties of the electron beam change completely shot to shot. While present state-of-the-art laser-plasma accelerators can already separately address guiding and control challenges by tweaking the plasma structures, the production of beams combining high quality and high energy is yet to be demonstrated. Here we use a new approach for guiding the laser, and combined it with a controlled injection technique to demonstrate the reliable and efficient acceleration of high-quality electron beams up to 1.1 GeV, from a 50 TW-class laser.
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