Construction of mapping systems of superconducting properties under magnetic fields

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The purpose of this study is to develop systems for visualizing supercurrent based on a femtosecond-laser excited terahertz radiation phenomenon, which we found in 1995. By focusing a laser spot to 20 micrometer in diameter and scanning the spot on a sample with detecting the THz radiation amplitude, we succeeded in visualizing two-dimensional supercurrent flow in high Tg superconducting films. Further, we succeeded in visualizing vector supercurrent flow under the flux trapped state by mapping two mutually orthogonal polarization components of THz radiation. The behavior of the supercurrent measured by this system is explained by the Bean model semi-quantitatively. The imaging system using the focused THz radiation is also developed and applied to visualize the photoexcited carrier distribution in semiconductors. These new applications of THz radiation will contribute to the growing THz technology.