Mechanism studies on hot electron generation by ultra-intense femtosecond laser interacting with solid target

The energy spectrum and the angular distribution of the hot electrons generated by an ultra-intense femtosecond laser interacting with a solid target are studied. The intensity of the femtosecond laser is 8.5×1018 W·cm-2 and the pulse duration is 30 fs in experiment. The temperature of the hot electrons at the normal of the target is 550 keV. Resonance absorption is the main mechanism that leads to the laser acceleration of the hot electrons at the normal of the target. And it accords with large plasma density scale length generated by pre-pulse which preceded the main pulse. The emission direction of the hot electron is normal to the rear surface for 30 μm target, and the emission peak disappears for 2 mm target.