High energy electron emission from water plasmas produced by femtosecond laser pulses

High energy electrons emitted from water plasmas produced by a single or multiple laser pulses are investigated. The multipulse mode greatly enhances the generation and temperature of the hot electrons. Directional emission of high energy electrons over 25 keV is observed in two symmetric directions with respect to the laser axis and at 46 degree from the directions of the laser electric field. Two-dimensional particle-in-cell simulations reproduce well the experimental results and indicate that the acceleration mechanism of the high energy electrons is mainly due to the resonance absorption at the edge of the spherical droplets formed by the leading pulse