OPTICAL CHARACTERIZATION OF LASER-DRIVEN ELECTRON ACCELERATION
M.C. Kaluza1,2,3, H.P. Schlenvoigt1,4, S.P.D. Mangles3, A.G.R. Thomas3,5, A.E. Dangor3, H. Schwoerer1,6, W.B. Mori7, Z. Najmudin3, K.M. Krushelnick3,5, A. Buck8,9, M. Nicolai1, K. Schmid8,9, C.M.S. Sears8, A.Sävert1, J.M. Mikhailova8, F. Krausz8,9, L. Veisz8
1 Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, 07743 Jena, Germany
2 Helmholtz-Institute Jena, Helmholtzweg 4, 07743 Jena, Germany
3 Department of Physics, Imperial College, London SW7 2AZ, United Kingdom
4 LULI, Ecole Polytechnique, 91128 Palaiseau cedex, France
5 Center for Ultrafast Optical Science (CUOS), University of Michigan, Ann Arbor, Michigan 48109, USA
6 Laser Research Institute, Stellenbosch University, Stellenbosch 7600, South Africa
7 Department of Physics and Astronomy, UCLA, Los Angeles, California 90095, USA
8 Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany
9 Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching, Germany
Abstract. We present the first experimental observation of the non-linear formation of a laser-driven plasma wave, its breaking which leads to the injection of electrons into this wave, and the subsequent acceleration of the electrons in the wave's electric field. The processes occurring during the interaction between the laser and the plasma are detected via the magnetic fields with purely optical methods leading to an unprecedented spatial and temporal resolution.
In a first experiment carried out at the JETI laser facility at IOQ Jena, Germany, the magnetic fields are generated both by the accelerated electron bunch and the displacement current present inside the plasma wave [1]. Results from a second experiment carried out with the LWS-20 laser system at MPQ Garching, Germany, show that under these conditions the main contribution to the magnetic fields comes from the accelerated electrons alone. Due to the available spatial and temporal resolutions we could show that the electrons are injected and accelerated in the first period of the plasma wave only. Furthermore, the duration of the electron bunch could be deduced to be as short as (2.5+0.8/-0.9) fs (r.m.s.) via the spatial extent of the magnetic-field feature [2].
These results are essential to improve the quality and stability of electron pulses generated with table-top laser systems which have the potential to be used as a source for brilliant and ultra-short x-rays.
References:
[1] M. C. Kaluza, H.-P. Schlenvoigt, S. P. D. Mangles, A. G. R. Thomas, A. E. Dangor, H. Schwoerer, W. B. Mori, Z. Najmudin, K. M. Krushelnick: “Measurement of Magnetic-Field Structures in a Laser-Wakefield Accelerator”, Physical Review Letters 105, 115002 (2010).
[2] A. Buck, M. Nicolai, K. Schmid, C. M. S. Sears, A. Sävert, J. M. Mikhailova, F. Krausz, M. C. Kaluza, L. Veisz: “Real-time observation of laser-driven electron acceleration”, accepted for publication in Nature Physics (2011)