Laser irradiation effects in crystalline and amorphous YBaCuO thin films

We have conducted a systematic study of the effects of laser irradiation on the properties of crystalline and amorphous YBaCuO thin films obtained by laser deposition. The irradiation experiments were mainly performed with a KrF and XeCl pulsed (25 us) excimer lasers producing energy densities of the order of 0.1 J/cm(2), but we used also Cu vapor green and Ar ion blue lasers with medium power output. In all cases the irradiation produced irreversible changes in the investigated samples. We measured structural, optical and transport properties of the irradiated films. After high dose laser treatment of crystalline (orthorhombic) films their superconducting properties as a rule deteriorated, but even small dose was sufficient for a marked improvement of surface smoothness. The response of amorphous films was more complex, dependent on the substrate and relied on the presence of crystalline clusters embedded in the amorphous matrix. X-ray diffraction studies of amorphous films revealed structural transformations caused by the interaction with laser light, and the results of optical spectroscopic measurements lead to interesting conclusions concerning the band structure in the investigated materials. Photon assisted structural transformations are suggested as the possible explanation of the observed effects.