SOME PROPERTIES OF ATOMIC BEAM PRODUCED BY LASER INDUCED ABLATION OF Li TARGET

Abstract

The beam production developed in our experiment is based on front surface illumination of Li target with low energy laser pulses so that no detectable plasma cloud is formed. This approach is similar to the works of Olstad [I], Meng 121, Selter 133, Leismann [4] and Dreyfus 153. The experimental set-up is shown in Fig. 1. Li target is placed in a vacuum vessel evacuated to a pressure of 10-orr. -Pulses from a TEA COz laser working at 10 Hz with energy in the 0.2 0.7 J range are directed onto the target after spatial filtering and attenuation. The diameter of the laser beam on the surface is roughly 1 mm2. Laser pulses consist of a main pulse of 150 ns duration and a 1 ps tail. About one half of the laser energy is contained in the main pulse. Taking into account spatial reduction and attenuation, the laser energy on the surface can be varied in the 2-7 mJ range (0.2 0.7 J/cm2 f luence) . This is low enough to avoid detectable plasma production. As a matter of fact, most of the laser energy as reflected from the surface, and only N 4% is absorbed.