DEVELOPMENT OF TUNABLE LOCAL OSCILLATOER OF THZWAVE BY PHOTOMIXING EXCITATION

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This project investigates ultrafast carrier dynamics in photon-microwave conversion materials, and develops a highly controllable and stable tunable oscillator and photon microwave converter based on new idea.We successfully observed THz radiation from several kinds of HTSs and Mn oxides. It was discovered that Josephson plasma emission can be optically-excited for TBCCO under weak magnetic field. The carrier dynamics was observed by time domain. THz spectroscopy. It was found that oxygen reduced HTS strongly enhances the THz emission intensity due to the decrease in THz reflection at the interface between superconductors and substrate.We also observed THz radiation and ultrafast photo-response of a-Ge. It was found that a-Ge has potential as a photomixing excitation material for the use of light source with 1.55μm wavelength.We developed a photon-microwave converter by fabricating the hybrid device of photo-mixer and HTS Josephson junction, and succeeded in the generation and detection of the microwaves extending up to 200 GHz. We demonstrated the high controllability and stability of the microwaves generated by using the fabricated devices. We proposed this photon-microwave converter as a potential system to detect accurate optical wavelength.We also proposed an 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.