title: Optical control of hard X-ray polarization by electron injection in a laser wakefield accelerator.
abstract: Laser-plasma particle accelerators could provide more compact sources of high-energy radiation than conventional accelerators. Moreover, because they deliver radiation in femtosecond pulses, they could improve the time resolution of X-ray absorption techniques. Here we show that we can measure and control the polarization of ultra-short, broad-band keV photon pulses emitted from a laser-plasma-based betatron source. The electron trajectories and hence the polarization of the emitted X-rays are experimentally controlled by the pulse-front tilt of the driving laser pulses. Particle-in-cell simulations show that an asymmetric plasma wave can be driven by a tilted pulse front and a non-symmetric intensity distribution of the focal spot. Both lead to a notable off-axis electron injection followed by collective electron-betatron oscillations. We expect that our method for an all-optical steering is not only useful for plasma-based X-ray sources but also has significance for future laser-based particle accelerators.
authors.affiliation: Institute of Optics and Quantum Electronics, Abbe-Center of Photonics, Friedrich Schiller University, Max-Wien Platz 1, 07743 Jena, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schnell
authors.forename: Alexander
authors.initials: A
authors.lastname: Sävert
authors.forename: Ingo
authors.initials: I
authors.lastname: Uschmann
authors.forename: Maria
authors.initials: M
authors.lastname: Reuter
authors.forename: Maria
authors.initials: M
authors.lastname: Nicolai
authors.forename: Tino
authors.initials: T
authors.lastname: Kämpfer
authors.forename: Björn
authors.initials: B
authors.lastname: Landgraf
authors.forename: Oliver
authors.initials: O
authors.lastname: Jäckel
authors.forename: Oliver
authors.initials: O
authors.lastname: Jansen
authors.forename: Alexander
authors.initials: A
authors.lastname: Pukhov
authors.forename: Malte Christoph
authors.initials: MC
authors.lastname: Kaluza
authors.forename: Christian
authors.initials: C
authors.lastname: Spielmann
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