Development of Laser Terahertz Technology

本课题总结了1999 ~ 2001年度“激光太赫兹技术的开发”科研资助项目的成果。通过项目成员的会议，对项目进行了报告。本项目的研究成果总结如下：1.阐明了超短激光脉冲激发高T_c超导体产生太赫兹辐射的特性，研制了高T_c超导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被开发出来，并应用于半导体、超导体、光子晶体和生物分子.通过改变外磁场、入射角、激光脉宽、温度等条件，研究了半导体InAs的太赫兹辐射特性，找到了最佳辐射条件，并发现在3 T附近辐射强度达到最大，当磁场强度达到15 T时，其太赫兹谱又减小又增大。3.半磁半导体Ga_ Mn_xAs的太赫兹谱研究<1-x>。结果表明，在临界温度附近，吸收发生了很大的变化，这一现象可以用载流子的跳跃来解释。实验<1-x>上明确了La_ Sr_xMnO_3晶格振动随抗磁绝缘相、铁磁金属相和铁磁绝缘相之间转变的变化.通过有机晶体DAST的非线性光学效应（差频混频），实现了20 THz以下的可调谐太赫兹辐射。通过该项目，日本全面认识到了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.