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

Projection optics is a means to reduce the spatial energy density variations on the target during laser ablation. Using projection optics to study the interaction between a spatially uniform 248 nm excimer laser beam and a YBa2Cu3O6+x target we observe a well-defined threshold fluence 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 target is conserved. The roughness of the deposited films increases along with the increase in roughness of the target above the threshold. Thus it is clear that in order to obtain flat stoichiometric films one should use a narrow fluence window just above the threshold.