Optical material, and, optical element, optical system and laminated diffractive optical element using it
An optical element of which diffraction efficiency hardly varies with wavelength is provided by using an optical material satisfying the conditions that n d >−6.667×10 −3 v d +1.70 and θ g,F ≦−2×10 −3 ν d +0.59 where n d is a refractive index at d-line, ν d is an Abbe number at the d-line, and θ g,F is a second order dispersion at d-line, whereby diffraction efficiency is improved in any working visible wavelength region and more precise chromatic aberration correction is obtained.
1. An optical material in which n d >−6.667×10 −3 ν d +1.70 and θ g,F ≦−2×10 −3 ν d +0.59, where n d is a refractive index at d-line, ν d is an Abbe number at the d-line and θ g,F is a second order dispersion at d-line, and said Abbe number (ν d ) is 22.7 or less.
2. The optical material according to claim 1 , wherein the optical material comprises a polymer and an inorganic nanoparticle material having a second order dispersion (θ g,F ) value of 0.45 or less.
3. An optical element comprising an optical material according to claim 1 , wherein said optical element is formed in a desired shape by a curing reaction.
4. The optical element according to claim 3 in which one surface is a diffracting surface having a diffractive shape.
5. The optical element according to claim 3 in which one surface is a refracting surface having a refractive shape.
6. An optical system comprising an optical element according to claim 3 and another optical element arranged in one and the same optical path.
7. The optical system according to claim 6 , wherein the system images an object.
8. The optical system according to claim 6 , wherein the system projects light onto an object.
9. A laminated diffractive optical element comprising:
a first diffractive optical element having a surface formed into a diffractive shape; and
a second diffractive optical element having a surface formed into a diffractive shape,
wherein the first diffractive optical element is made of an optical material in which n d >−6.667×10 −3 ν d +1.70 and θ g,F ≦−2×10 −3 ν d +0.59, where n d is a refractive index at d-line, ν d is an Abbe number at the d-line, and θ g,F is a second order dispersion at d-line;
the second diffractive optical element has an Abbe number larger than that of the first diffractive optical element; and
the diffracting surface of the first optical element and the diffracting surface of the second optical element are arranged in an opposite position, and said Abbe number (ν d ) is 22.7 or less.
10. The optical material according to claim 2 , wherein the polymer is polystyrene and the inorganic nanoparticle material is a transparent nanoparticle material.
11. The optical material according to claim 10 , wherein a size of the transparent nanoparticle material is from 2 to 50 nm.
12. The optical material according to claim 11 , wherein the transparent nanoparticle material is an ITO nanoparticle material.