Stability improvement of a laser-accelerated electron beam and the pulse width measurement of the electron beam

Kotaki, Hideyuki; Mori, Michiaki; Hayashi, Yukio; Kando, Masaki; Daito, Izuru; Fukuda, Yuji; Pirozhkov, A. S.; Koga, J. K.; Bulanov, S. V.

Laser wakefield acceleration is capable of generating electron bunches with high quality: quasi-monoenergetic, low in emittance, and a very short duration of the order of ten femto-seconds. Such femtosecond bunches can be used to measure ultrafast phenomena. We conducted experiments for stable electron bunch generation. When the target was nitrogen, the position and the energy were stable due to the long channel length. We have succeeded in generating a stable 40 MeV electron bunch for optimum plasma density. The electron beam oscillates in the electric field of the laser pulse. In energy space, the oscillation can be observed, and the electron energy spectrum can be converted to the electron pulse width. We have succeeded a measurement of the oscillation. The wave structure of the energy spectrum depends on the laser frequency. The pulse width (FWHM) of the electron is 1.5-cycles at a wavelength of 800 nm. The pulse width is 1.7 fs (rms).