Optical system having optical thin film including amorphous silicon oxide-based binder

摘要

An MgF₂ optical thin film is formed on an optical surface of a base material. The MgF₂ optical thin film includes MgF₂ particles and an amorphous silicon oxide-based binder which exists on the surfaces of the MgF₂ particles and between the MgF₂ particles. Owing to this amorphous silicon oxide-based binder, the optical thin film can have high mechanical strength and high adhesion to the base material, while having excellent environment resistance and a lower refractive index.