A study of the parameters of particles ejected from a laser plasma

Abstract

We report on the results concerning the characteristics and the behavior of expanding plasma generated by a Laser Ion Source (LIS). The LIS technique is an efficient means in producing of multi-charged ions utilizing pulsed laser beams. In order to extract Cu ions, in this experiment an XeCl excimer UV laser was employed, providing a power density on the target surface up to 5 × 108 W/cm2. Two typologies of diagnostic systems were developed in order to detect the plasma current and the ion energy. The time-of-flight (TOF) measurements were performed exploiting either a Faraday cup or an Ion Energy Analyzer (IEA). This latter allowed getting quantitative information about the relative ion abundances, their kinetic energy and their charge state. To study the plasma characteristics we measured the total etched material per pulse at 70 mJ. It was 0.235 μg and the overall degree of ionization, 16%. The angular distribution of the ablated material was monitored by optical transmission analysis of the deposited film as a function of the angle with respect to the normal to the target surface. Applying a high voltage to an extraction gap a multi-charged ion beam was obtained; different peaks could be distinguished in the TOF spectrum, resulting from the separation of ions of hydrogen, adsorbed compounds in the target and copper.