Observation of quasi-monoenergetic electrons in the plasma produced by sub-nanosecond laser pulse

We experimentally demonstrate the generation of quasi-monoenergetic electron bunch at the end of the electron energy distribution. The experiment was conducted at the Prague Asterix Laser System where iodine laser supplies laser energy up to 600 J at the fundamental wavelength of 1.315 μm with a pulse duration of 350 ps. The thickness of different target materials (Cu, Sn, Ta, Pb) was varied between 10 and 25 μm. The energy spectrum of electrons was measured using an array of electron spectrometers at different angular directions with respect to the laser axis. Three frame femtosecond interferometry driven by a Ti:Sa laser was implemented to scan the changes in electron density during plasma ignition by the iodine laser. The experimental results indicate the generation of well-defined quasi-monoenergetic peaks in the electron energy distribution. The energy range of the measured quasi-monoenergetic peaks lies between 0.6 and 1.5 MeV; however, the energy spread of the distribution varies between 4% and 12%. These features were observed consistently in the electron spectrum and illustrate the quasi-monoenergetic electron beam generation by interaction of a sub-nanosecond laser beam with plasma. In addition, a comparison of electron spectra from spectrometers located in opposite directions relative to the position of the laser focus indicates the splitting of the electron cloud into plasma blocks during the acceleration of hot electrons by Coulomb repulsion. These findings can be applicable in fast electron beam-driven radiation sources, electromagnetic pulse generation, charge particle acceleration, and inertial fusion studies.