Advanced Application of Laser-Excited Terahertz Waves

这项研究的目的是将本课题组开发的太赫兹光谱和成像新技术应用于先进的材料测量，以及新材料和生物样品的测量，并为更广泛的应用奠定基础。得到了以下结果1.在THz源的发展方面，通过在InAs表面上加装氧化镁半球形透镜，使其辐射功率提高了50倍。研究发现，随着外加磁场的增加，THz发射波形的极性在5T左右发生反转，由此可以看出，磁等离子体模式向晶体外辐射模式的转换在发射过程中起着重要作用。研制了温度为5~300K、磁场为±5T的THz磁光测量系统。它被应用于测量GaAs量子阱的回旋共振以及InAs和掺Si的GaAs的磁光效应。首次将太赫兹时间域谱方法应用于电子自旋共振(ESR)。研究了二维介质球光子晶体的透射谱。研究发现，随着介电常数的降低，介质平板的能带结构特征由限制模之一的跳跃自行车转变为类波导模，并研究了不同结构的金属孔阵。它们表现出多种传输特性，并阐明了它们的物理机制。测定了氨基酸、多肽、蛋白质等的光谱，阐明了它们的特征。特别是，我们证明了蛋白质动力学可以从太赫兹光谱中得到。采用连续多模激光二极管的小型化、低成本的太赫兹光谱仪性能得到了提高。

The aim of this research is to apply the new techniques of terahertz spectroscopy and imaging which the present research group has developed to advanced measurements of materials, and to measurements of new materials and bio specimens, and to establish foundations for broad applications. The following results are obtained.1. As to the development of THz sources, the 50 times enhancement of the radiation power from an InAs surface has been obtained by the attachment of an MgO hemispherical lens. It is found that the polarity of the THz emission waveform is reversed at around 5 T with increasing external magnetic field for n-InAs and, from this result it becomes clear that the conversion of the magnetoplasma modes to the radiation modes outside of the crystal is important in the emission process.2. The THz magnetooptical measurement system has been developed with variable temperature and magnetic field ranges of 5-300 K and ±5T, respectively. It was applied to the measurements of cyclotron resonance of GaAs quantum wells and the magnetooptical effects of InAs and Si-doped GaAs. The THz- time-domain spectroscopic method has been applied to the electron spin resonance (ESR) for the first time.3. Transmission spectra of two-dimensional dielectric sphere photonic crystals have been investigated. It is found that the feature of the band structure changes from the hopping-bike one of the confined modes to the waveguide-mode-like one of a dielectric slab with decreasing the dielectric constant Metal hole arrays with various structures have been investigated. They show a variety of transmission properties and the physical mechanisms of them are clarified.4. Spectra of amino acids, peptide, and proteins, etc. are measured and the characteristics of them are clarified. Especially, it is demonstrated that the protein dynamics can be obtained from the THz spectra.5. The performance of the compact and cheep THz spectrometer using CW multimode laser diodes is enhanced.