Abstract.  Laser plasma accelerators with colliding laser pulses scheme [1,2] produce today high quality and very stable electron beam with parameters that are controllable : charge, energy, energy spread can be control by adjusting either the injection laser beam parameters (intensity, polarization) or the plasma density [3]. Energy spreads in the 1% level with a peak current of a few kA are the typical values of our 200 MeV electron beam. Through the wide-band spectral measurements of coherent optical transition radiation (CTR), it has been shown that electron bunches produced using controlled optical injection have durations of only a few femtoseconds [4]. The shape and intensity of the measured CTR spectrum agrees with analytical modeling of electron bunches with durations of full width at half maximum of 3-4 fs. These measurements are supported by three-dimensional particle-in-cell simulations.

We anticipate that these results will have a strong impact on applications requiring short pulses and high peak currents, and will open prospects for future compact free-electron lasers.

References :
[1] E. Esarey et al., Phys. Rev. Lett. 79 (1997)
[2] J. Faure et al., Nature 444 (2006)
[3] C. Rechatin et al., Phys. Rev. Lett. 102 (2009)
[4] O. Lundh et al., submitted to Nature Physics