PREPARATION OF ISOTOPE TARGETS USING LASER-BEAM EVAPORATION TECHNIQUES

The advantages of a power laser for the preparation of vacuum deposited targets will be discussed. A power laser beam can be focused through an entrance lens into a vacuum chamber on very small samples (<1 mg). The distance between source and substrate can be extremely small during the evaporation process with the laser beam. There are no electric fields which might accelerate ionized particles. Thus a destruction of the substrate films or the backing foils can be prevented. In order to evaporate the material at a controlled rate parameters of the power laser as wave length, energy, power, power density, pulse width, and repetition rate have to be chosen carefully in order to obtain a reasonable evaporation process. Calculations show that a Nd : YAG laser with a power of 50 W, a divergence below 10 mrad, and the possibility of Q-switching will give reasonable results for the evaporation of isotopes and isotopic compounds with very low vapor pressures. First results of target preparation using a Nd : YAG laser will be reported for the example of two refractory materials, Os-metal and HfO2. © 1979.