Anti-reflection coating, and optical element and optical system with anti-reflection coating

1. An anti-reflection coating formed on an optical surface of an optical member for reducing an amount of light rays reflected from said optical surface, wherein:

for light rays in a wavelength range from 400 nm to 700 nm,

said anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees.

2. The anti-reflection coating set forth in claim 1 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers is formed by using a sol-gel method.

3. The anti-reflection coating set forth in claim 2 , wherein:

said optical member has a refractive index of approximately 1.52; and

said anti-reflection coating comprises:

a first layer, which is formed on said optical surface, said first layer having a refractive index of approximately 1.65 and an optical film thickness of approximately 0.27λ;

a second layer, which is formed on said first layer, said second layer having a refractive index of approximately 2.12 and an optical film thickness of approximately 0.07λ;

a third layer, which is formed on said second layer, said third layer having a refractive index of approximately 1.65 and an optical film thickness of approximately 0.30λ; and

a fourth layer, which is formed on said third layer, said fourth layer having a refractive index of approximately 1.25 and an optical film thickness of approximately 0.26λ;

“λ” being a reference light-ray wavelength of 550 nm.

4. The anti-reflection coating set forth in claim 3 , wherein:

said first layer is made from aluminum oxide by a vacuum deposition;

said second layer is made from a mixture of titanium oxide and zirconium oxide by vacuum deposition;

said third layer is made from aluminum oxide by vacuum deposition; and

said fourth layer is made from magnesium fluoride by a sol-gel method.

5. The anti-reflection coating set forth in claim 1 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers has a refractive index equal to or smaller than 1.3.

6. The anti-reflection coating set forth in claim 5 , wherein:

said optical member has a refractive index of approximately 1.52; and

said anti-reflection coating comprises:

a first layer, which is formed on said optical surface, said first layer having a refractive index of approximately 1.65 and an optical film thickness of approximately 0.27λ;

a second layer, which is formed on said first layer, said second layer having a refractive index of approximately 2.12 and an optical film thickness of approximately 0.07λ;

a third layer, which is formed on said second layer, said third layer having a refractive index of approximately 1.65 and an optical film thickness of approximately 0.30λ; and

a fourth layer, which is formed on said third layer, said fourth layer having a refractive index of approximately 1.25 and an optical film thickness of approximately 0.26λ;

“λ” being a reference light-ray wavelength of 550 nm.

7. The anti-reflection coating set forth in claim 6 , wherein:

said first layer is made from aluminum oxide by a vacuum deposition;

said second layer is made from a mixture of titanium oxide and zirconium oxide by vacuum deposition;

said third layer is made from aluminum oxide by vacuum deposition; and

said fourth layer is made from magnesium fluoride by a sol-gel method.

8. The anti-reflection coating set forth in claim 1 , wherein:

said optical member has a refractive index of approximately 1.52; and

said anti-reflection coating comprises:

a first layer, which is formed on said optical surface, said first layer having a refractive index of approximately 1.65 and an optical film thickness of approximately 0.27λ;

a second layer, which is formed on said first layer, said second layer having a refractive index of approximately 2.12 and an optical film thickness of approximately 0.07λ;

a third layer, which is formed on said second layer, said third layer having a refractive index of approximately 1.65 and an optical film thickness of approximately 0.30λ; and

a fourth layer, which is formed on said third layer, said fourth layer having a refractive index of approximately 1.25 and an optical film thickness of approximately 0.26λ;

“λ” being a reference light-ray wavelength of 550 nm.

9. The anti-reflection coating set forth in claim 8 , wherein:

said first layer is made from aluminum oxide by a vacuum deposition;

said second layer is made from a mixture of titanium oxide and zirconium oxide by vacuum deposition;

said third layer is made from aluminum oxide by vacuum deposition; and

said fourth layer is made from magnesium fluoride by a sol-gel method.

10. An optical element comprising an optical member having an optical surface which is a plane or a curved surface, and an anti-reflection coating which is formed on the optical surface of said optical member for reducing an amount of light rays reflected from said optical surface, wherein:

for light rays in a wavelength range from 400 nm to 700 nm,

said anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees.

11. The optical element set forth in claim 10 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers is formed by using a sol-gel method.

12. The optical element set forth in claim 10 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers has a refractive index equal to or smaller than 1.3.

13. An optical system comprising an optical element, which is positioned between an object and an image plane, wherein:

at least one optical surface of said optical element is provided with an anti-reflection coating; and

for light rays in a wavelength range from 400 nm to 700 nm,

said anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees.

14. The optical system set forth in claim 13 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers is formed by using a sol-gel method.

15. The optical system set forth in claim 13 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers has a refractive index equal to or smaller than 1.3.

16. The optical system set forth in claim 13 to be used for light rays in a wavelength range from 400 nm to 700 nm.

17. The optical system set forth in claim 13 , said optical system constituting an imaging optical system.

18. The optical system set forth in claim 13 , said optical system constituting a viewing optical system.

19. An optical system comprising a plurality of optical surfaces, wherein:

at least one of an n-th ghost-generating surface and an m-th ghost-generating surface of said optical surfaces is provided with an anti-reflection coating; and

for light rays in a wavelength range from 400 nm to 700 nm,

said anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees; and

said optical system satisfies the following formula

Rn×Rm ≦0.10[%]

with “Rn” representing the reflectance of said n-th ghost-generating surface and “Rm” representing the reflectance of said m-th ghost-generating surface.

20. The optical system set forth in claim 19 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers is formed by using a sol-gel method.

21. The optical system set forth in claim 19 , wherein:

said anti-reflection coating comprises multiple layers; and

at least one of said layers has a refractive index equal to or smaller than 1.3.

22. The optical system set forth in claim 19 to be used for light rays in a wavelength range from 400 nm to 700 nm.

23. The optical system set forth in claim 19 , said optical system constituting an imaging optical system.

24. The optical system set forth in claim 19 , said optical system constituting a viewing optical system.

25. A method for reducing an amount of light rays reflected from an optical surface of an optical member, the method comprising:

forming an anti-reflection coating on said optical surface such that, for light rays in a wavelength range from 400 nm to 700 nm, the anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees.

26. The method according to claim 25 , wherein the anti-reflection coating includes multiple layers, at least one of said layers being formed by a sol-gel method.

27. The method according to claim 25 , wherein the anti-reflection coating includes multiple layers, at least one of said layers having a refractive index equal to or smaller than 1.3.

28. A method for forming an optical element, comprising:

providing an optical member having an optical surface which is a plane or a curved surface, and

forming an anti-reflection coating on said optical surface of said optical member such that for light rays in a wavelength range from 400 nm to 700 nm, the anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees.

29. The method according to claim 28 , wherein the includes multiple layers, at least one of said layers being formed by a sol-gel method.

30. The method according to claim 28 , wherein the includes multiple layers, at least one of said layers having a refractive index equal to or smaller than 1.3.

31. A method for forming an optical system, comprising:

providing an optical element, which is positioned between an object and an image plane,

wherein at least one optical surface of said optical element is provided with an anti-reflection coating, and

for light rays in a wavelength range from 400 nm to 700 nm, the anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees.

32. The method according to claim 31 , wherein the anti-reflection coating includes multiple layers, at least one of said layers being formed by a sol-gel method.

33. The method according to claim 31 , wherein the anti-reflection coating includes multiple layers, at least one of said layers having a refractive index equal to or smaller than 1.3.

34. A method for forming an optical system having a plurality of optical surfaces, the method comprising:

providing at least one of an n-th ghost-generating surface and an m-th ghost-generating surface of said optical surfaces with an anti-reflection coating,

wherein for light rays in a wavelength range from 400 nm to 700 nm, the anti-reflection coating has:

a reflectance of 0.5% or less if said light rays are incident on said optical surface at angles within a range from 0 to 25 degrees, and

a reflectance of 3.5% or less if said light rays are incident on said optical surface at angles within a range from above 25 degrees to 60 degrees, and

the following formula is satisfied:

Rn×Rm≦ 0.10[%]

“Rn” representing the reflectance of said n-th ghost-generating surface, and “Rm” representing the reflectance of said m-th ghost-generating surface.