SUPERCARRIER MODULATION WITH A FEMTOSECOND LASER AND ITS APLLICATIONS FOR NEW FUNCTIONAL PHOTONIC DEVICES

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This project investigates terahertz radiation from high-Tc superconductors (HTSs), ultrafast carrier dynamics in HSTs, optical vortex generation due to ultrafast optical supercurrent modulation, proposal and developments of new photonic devices and systems.We successfully observed THz radiation from YBCO, TBCCO, BSCCO, and Pr doped YBCO, and discovered optically-excited Josephson plasma emission from TBCCO under weak magnetic flied. The carrier dynamics was observed in time domain with a time resolution of 100 fs using pump and probe THz emission spectroscopy. It was found that Pr-doping into YBCO strongly enhances THz emission intensity, which is attributable to the decrease in THz reflection at the interface between superconductors and substrate. We discovered new effect in optical vortex generation, can to be explained by the conventional rule of superconductivity. The mechanism was explained by ultrafast optical supercurrent modulation. We proposed to apply this new effect to detec … More t and process femtosecond optical signals, and demonstrated to detect a single shot femtosecond optical signal via otpcal vortec generation.As an application research we developed Laser-Terahertz Emission Microscope (LTEM) and observed supercurrent distribution ih high-Tc superconductors. It proven that the LTEM is a potential tool to observe supercurrent and vortices in HTSs as the noncontact, nondestructively and free-space evaluation system.We also developed photon microwave converter by fabricating photomixer and HTS Josephson junction hybrid device. We proposed this photon microwave converter as a potential system to detect accurate optical wavelength.We propose optically-controlled-terahertz flux-flow transistor as an optical direct interface between optical communication signals and single flux quantum logic circuits. The preliminary device was fabricated and tested under optical excitation.The results obtained here has opened new research field "Superconductor Photonics", which will provide a key breakthrough for terahertz technology. Less