Mass composition and ion energy distribution in plasmas produced by pulsed laser evaporation of solid materials

Abstract

The mass composition and the ion energy distribution of plasmas produced by pulsed laser (TEA CO2-laser) evaporation of solids have been measured using a customized mass/energy analyzer. This analyzer consists of a modified cylindrical mirror analyzer (CMA) and a quadrupole mass spectrometer (QMS) and is able to measure the mass resolved energy distribution (up to 1 keV) of positive ions as well as the mass spectrum (up to 300 amu) at a particular energy. Plasmas were produced from Al, C, Au/Ge composite, Al2O3, SiO2, TiO2, MgF2 and YBa2Cu3O7 targets using a pulsed CO2-laser with a maximal laser power density at the target surface of about 108 W cm−2. The measurements are carried out in a vacuum chamber (Bell jar) at a pressure of the order of 10−3 Pa. The results indicate that the plasma formation induced by the laser pulse is accompanied by dissociation of the molecules of the target material. The plasmas mainly consist of single and multiple (up to triple) charged atomic ions with energies ranging from several eV's up to several hundred eV's. The influence of the laser power density on the ion energy distribution was investigated for several targets.