Raman study of laser irradiation effects on YBa2Cu3O7-x thin films

The effects of laser irradiation on high-temperature superconducting YBa2Cu3O7-x thin films have been investigated by micro-Raman spectroscopy. Laser heating affects YBa2Cu3O7-x thin films to varying degrees at different laser power levels. For a laser power density below 1 mW mu m(-2), laser irradiation causes only thermal expansion within the focused area. When the laser power density is increased to about 1.7 mW mu m(-2) oxygen out-diffusion occurs. The orthorhombic to tetragonal structural phase transition was observed at 3.1 mW mu m(-2). Above 4.3 mW mu m(-2), chemical decomposition is inferred from the appearance of Raman bands due to the impurity phase BaCuO2. Comparison between the laser-heated results and the furnace-heated results was made, and the role played by temperature gradient and stress in the laser-heated sample is discussed in detail.