Laser-Induced Oxygen Control in Small Region of $\bf YBa_{2}Cu_{3}O_{\ninmbi y}$ Poly- and Single Crystals, Observed by Microscopic IR Reflection

We have studied the oxygenation and deoxygenation induced by laser irradiation in poly- and single crystals of YBa2Cu3Oy by microscopic IR reflection. We have observed a dramatic appearance and disappearance of the lattice-phonon modes unique to the insulator phase in accordance with the change of conductivity induced by the irradiation. By this method, we could detect the mutual conversion of the phase in an area as small as 0.1 x 0.1 mm(2) without using electrodes, which is suitable for the study of the oxygenation and deoxygenation, particularly between y=similar to 6.2 to y=similar to 6.5. The differences in the conversion behaviors between single and polycrystals are discussed.