Infrared optical film with low refractive index and preparation method thereof

The invention discloses an infrared optical film with a low refractive index and a preparation method thereof and belongs to the field of optical films. The infrared optical film with the low refractive index is prepared by means of the effective preparation method and by adopting a rare earth element fluoride YF3, and the infrared optical film, with the low refractive index, prepared by means ofthe method has characteristics of an amorphous structure and smaller scattering loss in comparison with that of the films of a single crystal structure and the films of a polycrystalline structure; the refractive index coefficient of the film with the thickness of 1.5 microns is 1.482 and is equivalent to that of existing mid-infrared laser optical films with low refractive indexes, and the designed degree of freedom of the infrared optical film is the same as that of the existing mid-infrared laser optical films with the low refractive indexes; however, the surface roughness and aggregation density of the infrared op