Small-divergence electron beams produced by multiphoton excitation of metallic surfaces

Abstract

The angular distribution of photoelectrons produced by laser-induced four-photon excitation in gold metalic targets is reported. Laser-target interaction time effects have been investigated by using two Nd:YAG lasers emitting at 1.06 μm pulses of 35 ps and 20 ns duration. Both lasers produced four-photon electron angular distributions of 9°±2° full width at half maximum. This width was independent from the intensity of the picosecond laser up to the breakdown threshold at a laser intensity of 1.4 GW/cm2. In contrast, the distribution produced by the nanosecond pulses was broadened at intensity levels higher than 60 MW/cm2, which is indicative of a significant contribution from thermionic emission. These results are compared to those obtained by D. Charalambidis, E. Hontzopoulos, C. Fotakis, Gy. Farkas, and Cs. Tóth [J. Appl. Phys. 65, 2843 (1989)], for single photon excitation by using a KrF excimer laser.