Transmission-Property Measurements of Crystal Quartz and Plastic Material in the Terahertz Region

To date, a few optical materials have been used for THz (terahertz) optics. The limited numbers of light sources developed in the THz region have resulted in a lack of optics. We have developed a compact high-power FEL (free-electron laser) operating in the frequency range of 0.3 ∼ 3 THz, which is a powerful tool for investigating the optical properties of materials in the THz spectral range. We measured the transmittances of crystal quartz and plastic material by using the THz FEL. We discuss the dependence of transmission upon the polarization of the FEL beam and the effect of multiple-beam interference observed from a thin specimen. We also report data from FTIR (Fourier-transform infrared) spectroscopy of the materials in the THz region