LASER-ABLATION THRESHOLD OF YBA2CU3O6+X

Using projection optics we made a detailed study of the interaction of a spatially uniform 248 nm excimer laser beam and a 99% dense YBa2Cu3 O6+x target. Below a threshold fluence of 1 J/cm2 the roughness of the irradiated target increases dramatically due to non-stoichiometric ab lation. The overall target surface composition becomes increasingly Y rich and Cu poor, while the opposite is found for the corresponding ab lated thin films. Above the threshold fluence the composition of the a blated target surface is conserved. As a result of the energy homogene ity of the laser beam obtained by means of projection optics, the opti mization of the deposition parameters has been improved leading to the reproducible fabrication of flat, stoichiometric YBa2Cu3O7 films with T(c0)'s over 91 K.