THE LASER-ABLATION THRESHOLD OF YBA2CU3O6+X AS REVEALED BY USING PROJECTION OPTICS

Projection optics is a means to reduce the spatial energy density vari ations on the target during laser ablation. Using projection optics to study the interaction between a spatially uniform 248 nm excimer lase r beam and a YBa2Cu3O6+x target we observe a well-defined threshold fl uence of 1.0 J/cm(2). Below this threshold non-stoichiometric ablation results in an dramatic change in target morphology and in a decay of the ablation rate. Above this threshold the stoichiometry of the targe t is conserved. The roughness of the deposited films increases along w ith the increase in roughness of the target above the threshold. Thus it is clear that in order to obtain flat stoichiometric films one shou ld use a narrow fluence window just above the threshold.