Development of Laser Terahertz Technology

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In this project, we summarized the result of the project supported by Grant-in-Aid for Scientific Re search for Priority Area "Development of Laser Terahertz Technology"(FY1999-FY2001). Through the meeting by the project members, a report of the project is made. The results of the project are summarized as follows.1. The characteristics of the terahertz radiation from high-To superconductors excited by ultrashort laser pulses have been clarified and the apparatus for visualizing supercurrent distribution in high-Tc superconducting films has been developed. The various terahertz spectroscopic and imaging systems for various purposes are also developed and applied to semiconductors, superconductor, photonic crystals and biomolecules.2. The characteristics of the terahertz radiation from the semiconductor InAs are investigated by changing external magnetic field, incident angle, laser pulse width, temperature etc, and the condition for the most appropriate radiation has been found. It is also found that the radiation intensity becomes maximum at about 3 T, and decreases and increases again with further increasing the magnetic field up to 15 T.3.The terahertz spectroscopy of the semimagnetic semiconductor Ga_<1-x>Mn_xAs has been done. It is found that the absorption changes largely near the critical temperature and this result is explained by the carrier hopping. The change of the Lattice vibration of La_<1-x>Sr_xMnO_3 with the transitions among the diamagnetic insulating, ferromagnetic metallic and ferromagnetic insulating phases has been made clear experimentally.4. The tunable terahertz radiation up to 20 THz is realized by the nonlinear optical effect (difference frequency mixing) by the organic crystal DAST.Through this project, the importance of the terahertz technology is realized overall in Japan.