Mgf2 Optical Thin Film Including Amorphous Silicon Oxide Binder, Optical Element Provided With the Same, and Method for Producing Mgf2 Optical Thin Film

Abstract

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.

Description

TECHNICAL FIELD [0001] The present invention relates to a singlelayered or multilayered optical thin film formed of MgF2, a method for producing the same, an optical element having the MgF2 optical thin film, and an optical system for optical instruments such as cameras, microscopes, binoculars, and exposure apparatuses which is provided with the optical element. BACKGROUND ART [0002] Surfaces of individual lenses, which construct an optical system such as a camera lens and an objective lens of a microscope, are coated with an antireflection film in order to reduce the reflection. In general, the optical thin film such as the antireflection film is produced by the dry method (dry process), in which the vacuum vapor deposition method, the sputtering method, the CVD method (Chemical Vapor Deposition) or the like is used. [0003] In order to obtain a high performance optical thin film having a low reflectance in a wide wavelength band or a wide angle band, it is known that a multilayere...

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Benefits of technology

[0028] According to a first aspect of the present invention, there is provided an MgF2 optical thin film, comprising MgF2 minute particles; and an amorphous silicon oxide-based binder which exists between the MgF2 minute particles.

[0029] According to the present invention, the MgF2 minute particles, which are excellent in the environment resistance (durability), are used as the main constitutive substance of the film, and the MgF2 minute particles are bonded or connected to one another by the amorphous silicon oxide-based binder. Therefore, the strong bonding or connection can be provided between the MgF2 minute particles and between the MgF2 minute particles and the base material. The mechanical strength of the film and the adhesive force between the film and the base material are improved. That is, it is considered that the MgF2 optical thin film has such a structure that the voids (gaps) are present between the MgF2 minute particles, and the voids are filled with the amorphous silicon oxide-based binder. SiO2, which is somewhat inferior in the environment resistance, can be used as the amorphous silicon oxide-based binder. However, it is enough to use a small amount of the binder as compared with the MgF2 minute particles. Therefore, it is possible to sufficiently secure the environment resistance as the entire thin film.

[0030] In the MgF2 optical thin film of the present invention, the MgF2 minute particles may be connected by the amorphous silicon oxide-based binder, and the amorphous silicon oxide-based binder, disposed on surfaces of MgF2 minute particles, among the MgF2 minute particles, which exist at an outermost portion of the MgF2 optical thin film, may have a thickness which is not more than 5% of a wavelength of light to be radiated. Further, in the MgF2 optical thin film of the present invention, the amorphous silicon oxide-based binder, which exists between adjacent MgF2 minute particles, among the MgF2 minute particles, may have a thickness which is smaller than a particle diameter of the MgF2 minute particles. When the thickness of the binder is adjusted as described above, it is possible to lower the refract

Problems solved by technology

However, in the case of the film using MgF2 as described in International Publication No. 02/18982A1, the film strength and the adhesive force with respect to the base material are insufficient, although the refractive index of the optical thin film can be lowered to be not more than 1.30.

In the case of the films in which the film strength and the adhesive force with respect to the base material can be secured as described in Japanese Patent No. 3272111, Japanese Patent Application Laid-open No. 11-6902, Japanese Patent Application Laid-open No. 7-48527, Japanese Patent Application Laid-open

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