Optical Physics Laboratory, Department of Physics, Faculty of Science
Development of Terahertz Time Domain Spectroscopy
  When femtosecond optical pulses are illuminated on semiconductor's surface, the electromagnetic waves at terahertz frequencies are emitted into free space. By using this phenomenon, the extremely broadband spectroscpy in terahertz range can be achieved.
  In our lab, we are developing this terahertz time domain spectrosopic system. In this system, we can measure the waveform of THz waves directly in time domain, and correspondingly, obtain the intensity and phase spectra sinultaneously. For solid state physics, we can measured both the real and imaginary part of refractive index and/or electoric permitivity of samples without other assumption and analysis.
  In our lab, now we develop smaller and faster THz-TDS system. and try to bring the THz-TDS to some practical applications.

Figure. Schematic of optical setup of THz time domain spectroscopy
Photonic Crystals & Plasmonic Crystals
 The energy band structure can be made for electromagnetic waves as electrons have an energy band structure in solid state physics. This is called a photonic band structure, and made by fabricating the periodic structure of dielectrics. Such a material, called photonic crystal, has focused tremendous attentions in recent years.

When such a periodic artificial structure is made of metal, it is called plasmonic crystal. In our lab, we investigate the very interesiting optical characteristics of such materials, and developing the application for, especially, THz technology.

Figure. Photonic crystal made with Si
 Metamaterials are artificial structures that can realize the optical and electromagnetic characteristics that are never achieved with materials in nature.
  For example, we can realize the material that has negative electric permittivity and negative magnetic permeability. Such a material is called a negative refractive index (NRI) material or left-handed material. In addition, metamaterials can realize other many interesting phenomena, e.g. cloaking, chiral materials, near-zero-epsilon materials etc.
  In our lab, we investigate the interesting optical properties of metamaterials in THz region.

Figure. 3D magnetic metamaterials operating in THz region
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