Si-O containing hydrogenated carbon film, optical device including the same, and method for manufacturing the Si-O containing hydrogenated carbon film and the optical device

An Si-O containing hydrogenated carbon film as an optical film has a refractive index in a range from at least 1.48 to at most 1.85 for light of 520 nm wavelength and an extinction coefficient of less than 0.15 for light of 248 nm wavelength, wherein the refractive index and the extinction coefficient are decreased with energy beam irradiation. By utilizing such an Si-O containing hydrogenated carbon film, it is possible to provide various types of optical elements and an optical device including the same.