Smallhyphen;divergence electron beams produced by multiphoton excitation of metallic surfaces

摘要

The angular distribution of photoelectrons produced by laserhyphen;induced fourhyphen;photon excitation in gold metalic targets is reported. Laserhyphen;target interaction time effects have been investigated by using two Nd:YAG lasers emitting at 1.06 mgr;m pulses of 35 ps and 20 ns duration. Both lasers produced fourhyphen;photon electron angular distributions of 9deg;plusmn;2deg; 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. Toacute;th lsqb;J. Appl. Phys.65, 2843 (1989)rsqb;, for single photon excitation by using a KrF excimer laser.