Velocity Selection of Laser Ablated Metal Atoms by a Novel Non-Mechanical Technique

Abstract

AbstractWe present the results of experiments on velocity selection of fast laser ablated al, Ga, and in atoms by a novel, non-mechanical, technique. Pulses of atoms with broad velocity distributions are produced by laser ablation of a single component pure metal target in vacuum. after a delay of ~ 1 μs, there exists a strong one-to-one correlation between atomic velocity and distance traveled from the ablated surface. Thus, a second pulsed laser, delayed by ~ 1 μs and crossed at a right angle to the atomic beam, can be used to photoionize only those atoms with unwanted velocities, i.e.: atoms moving too fast or too slow to be hidden behind an opaque mask placed ~ 1 cm from the ablated surface. the photoions, and any ions surviving from the ablation event, are subsequently deflected from the beam by a static magnetic field. by a fortunate coincidence, al, Ga, and in atoms all have very large single photon photoionization cross sections at 193 nm, the output wavelength of the arF excimer laser; thus, well over 95% of the unwanted atoms can be easily photoionized and rejected. We have demonstrated velocity selected al, Ga, and in atom fluxes equivalent to Ф ~ 1011 atoms/(cm2-eV-pulse) at a working distance of 10 cm.