Development of a new device with contact grating for terahertz wave generation

Yoshida, Fumiko; Tanaka, Momoko; Nagashima, Keisuke

We have proposed a new device with contact grating for intense terahertz wave generation. It is important to prepare the contact grating with a high refractive index material because high diffraction efficient is expected with higher refractive index. Therefore, we focused on TiO rutile crystal, which has the highest refractive index within oxidized materials. However, there are no TiO rutile thin films with higher refractive index than 2.5 at about 1 um. We adopted a method of oxidizing a Ti thin film, in which a Ti thin film was deposited by electronbeam evaporation and annealed in air for crystallization to a rutile crystal. Various TiO thin films were prepared under different conditions. The annealing temperature, annealing time, and heating rate of the Ti thin films were optimized to obtain a transparent TiO thin film with a high refractive index, and low coefficients of absorption and scattering. The highest refractive index was achieved by this method.