Advanced Application of Laser-Excited Terahertz Waves

本研究的目的是将本研究小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，并为广泛应用奠定基础。得到了以下结果：对于太赫兹源的开发，通过附着氧化镁半球面透镜，获得了从InAs表面辐射功率提高50倍的结果。研究发现，随着外加磁场的增加，n-InAs的太赫兹发射波形的极性在5t左右发生反转，从这个结果可以清楚地看出，在发射过程中，磁等离子体模式向晶体外辐射模式的转换是重要的。研制了变温度、变磁场范围分别为5-300 K和±5T的太赫兹磁光测量系统。应用该方法测量了砷化镓量子阱的回旋共振以及InAs和si掺杂砷化镓的磁光效应。第一次将太赫兹时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光谱。研究发现，随着介电常数的减小，带结构的特征从局限模的跳波型转变为类波导模的介质板带结构。它们表现出多种传输特性，并阐明了它们的物理机理。测定了氨基酸、多肽、蛋白质等的光谱，阐明了它们的特性。特别是，从太赫兹光谱中可以得到蛋白质的动力学。采用连续波多模激光二极管的太赫兹光谱仪结构紧凑、价格低廉，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.