Effect of target purity on laser-produced plasma expansion

Abstract

The effects of target surface impurities on the laser-produced plasma were studied by means of Thomson ion spectrograms and time-of-flight measurements of the plasma ions. Hydrocarbons were believed to be the most likely surface impurity. Consequently, polyethylene was used to characterise an impure target. For comparison, pure targets (5 to 20 ppm impurities) of C, Ti, and Ta and a standard quality Ti target were used. The fastest Cz+ ions from the plasma expansion using a polyethylene target had the same peak velocity. When the hydrogen impurity was removed from a carbon target, the fastest CZ+ ions had an energy proportional to their charge in agreement with the isothermal expansion model. Also, the presence of hydrogen affected the lateral transport of the plasma.

Temperature and centre-of-mass energy of ions emitted by laser-produced polyethylene plasma

“…It is known that the complete charge-state spectrum of ions can be recorded far from the irradiated target even though the plasma temperature is so high that light elements should be fully ionized [1,5]. Moreover, recent experiments have shown that the expanding plasmas of medium and heavy elements consist of multiply charged as well as highly charged ions [6].…”

The influence of surface contamination on the ion emission from nanosecond-pulsed laser ablation of Al and Cu

“…As already mentioned, the intensity of the target ions is also sensitive to the surface contamination [1,19]. At a vacuum pressure of the order of 10 −6 mbar, the surfaces are known to be covered with a thin layer of adsorbates [28,29]. In accord ance with the kinetic theory of gases, the impingement rate of the residual gas atoms on a surface is given as…”