Optical Parameters of Gas Hydrates for Terahertz Applications

It is necessary to know the terahertz dielectric constants of ice and various gas hydrates to understand their fundamental chemical and physical properties and their various possible applications. In this paper, we compare and discuss the frequency dependence and temperature dependence of the optical properties of several hydrogen-bonded solid crystals such as ice, propane hydrate and methane hydrate in the terahertz wave region. The refractive indices of ice and propane hydrate were found to be similar, while that of methane hydrate was slightly lower. The reflectivity of methane hydrate was as low as 15% that of ice, and this difference may be useful in various applications. All samples showed the same tendency with respect to the temperature dependency of their refractive indices. There was no large difference in absorption, and all samples exhibited the same frequency dependence and temperature dependence.