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.

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