Angular and energy distribution of fast electrons emitted from a solid surface irradiated by femtosecond laser pulses in various conditions

Angular and energy distributions of fast electrons generated from the interaction of 60 fs, 795 nm laser pulses with aluminum targets have been experimentally investigated in various conditions. Increasing laser intensities from the nonrelativistic to the relativistic, a transition of the angular distribution of outgoing fast electrons from the specular reflection direction to the target normal has been observed for p-polarized laser irradiation. The fast electrons' energy spectrum at high laser intensity, e.g., ∼2.6x1018 W/cm2, consists of two peaks, which are found to originate from the target normal with low energy and specular reflection direction with high energy, respectively. By adding a prepulse to generate preplasma, the electron yields at the direction of the reflected laser can be greatly enhanced, and a double-peak angular distribution is observed. Besides, a more collimated electron emission peak in the specular reflection direction can be obtained by employing a larger f-number focusing system.