Development of Laser Terahertz Technology

本项目总结了1999- 2001年度国家科学研究资助重点领域“激光太赫兹技术发展”项目的研究成果。通过项目成员的会议，对项目进行报告。项目成果总结如下：1。阐明了超短激光脉冲激发高至超导体的太赫兹辐射特性，研制了高至超导体薄膜中超电流分布的可视化装置。各种用途的太赫兹光谱和成像系统也得到了发展，并应用于半导体、超导体、光子晶体和生物分子。通过改变外加磁场、入射角、激光脉冲宽度、温度等因素，研究了半导体InAs的太赫兹辐射特性，找到了最合适的辐射条件。辐射强度在3 T左右达到最大值，并随着磁场的进一步增大而减小，直至15 T。对半磁半导体Ga_<1-x>Mn_xAs进行了太赫兹光谱分析。发现在临界温度附近吸收变化很大，这一结果可以用载流子跳变来解释。实验明确了La_<1-x>Sr_xMnO_3晶格振动随抗磁绝缘相、铁磁金属相和铁磁绝缘相转变的变化规律。利用有机晶体DAST的非线性光学效应（差频混频）实现了20太赫兹的可调谐辐射。通过该项目，日本全面认识到太赫兹技术的重要性。

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.