Temporal characteristics of monoenergetic electron beams generated by the laser wakefield acceleration

Abstract

Pulse length of quasimonoenergetic electrons accelerated by the wakefield generated by 12 TW, 40 fs laser pulses in a gas jet is determined via spectral measurements using a bolometer to detect coherent transition radiation. A quasimonoenergetic electron beam with its mean energy E 21 MeV, dispersion E 4 MeV, total charge q 30 pC, and the geometrical emittance 0:07 mm mrad is generated with high reproducibility. The averaged duration of only the quasimonoenergetic electron bunches peaked around 20 MeV is 130 30 fs (FWHM), while it is 250 70 fs (FWHM) for electron bunches with quasimonoenergetic distributions peaked around 4 MeV, at a distance of 180 mm far from the gas jet because of relatively large electron energy spread. Pulse elongation of the electron bunch with the quasimonoenergetic distribution after 180 mm path is 60-220 fs (FWHM). Therefore, the initial duration of the electron bunch at the gas-jet rear is expected to be less than 100 fs (FWHM).

Diagnostics of electron beams and plasma wave in laser-plasma accelerators

“…Therefore careful CTR spectral measurements delivering this spectral jump and also the bunch duration. Laser-generated electron bunch durations from few-100 fs down to few-fs have been obtained applying this technique [26,27]. This simple and robust approach provides the duration in an indirect measurement after the acceleration region.…”

“…Simple considerations and simulations indicate that acclerated quasi-monoenergetic electron bunches are shorter than the resolution of these previous approaches, which triggered further development. Another CTR based method utilized the spectrum of the radiation [26,27]. The coherent nature of this radiation requires that the electrons in a bunch emit in phase, which needs a shorter bunch duration than the radiation wavelength.…”

Control of Laser Plasma Based Accelerators up to 1 GeV

“…Ultrafast pulse radiolysis [110,111] using high quality e-beams from LWFA has been pursued at U-Tokyo [112]. The pulse duration of quasimonoenergetic e-beam (peak energy of 20 MeV with 20% energy spread, 30 pC) was measured to be 130 fs after the propagation of 180 mm [113]. For femtosecond pump probe experiments, higher quality e-beams may be required.…”

Electron Acceleration Using an Ultrashort Ultraintense Laser Pulse

“…An electron pulse duration is measured with an electro-optical sampling technique using CTR in the THz region, and the temporal resolution of several tens of femtoseconds has been achieved. (Debus et al, 2010;van Tilborg et al, 2006) An electron pulse duration is also estimated from the spectrum of CTR (Glinec et al, 2007;Ohkubo et al, 2007). Recently, generation of a few femtosecond electron pulse has been demonstrated using an optical injection scheme (Lundh et al, 2011).…”