Anti-reflection coating, optical member having it, and optical equipment comprising such optical member

1. An anti-reflection coating comprising first to ninth layers laminated in this order on a substrate for having reflectance of 0.2% or less to light in a visible wavelength range of 390-720 nm,

said second, fourth, sixth and eighth layers being high-refractive-index layers each formed by a high-refractive-index material having a refractive index of 2.21-2.70 to a helium d-line having a wavelength of 587.56 nm;

said first, third, fifth and seventh layers being intermediate-refractive-index layers each formed by an intermediate-refractive-index material having a refractive index of 1.40 or more and less than 1.55 to said d-line; and

said ninth layer being a low-refractive-index layer formed by a low-refractive-index material having a refractive index of 1.35 or more and less than 1.40 to said d-line;

wherein the refractive index difference between said intermediate-refractive-index layers and said high-refractive-index layers is 0.67-1.30.

2. The anti-reflection coating according to claim 1 , wherein said high-refractive-index material is TiO 2 , Nb 2 O 5 , or a mixture or compound of at least two of TiO 2 , Nb 2 O 5 , CeO 2 , Ta 2 O 5 , ZnO, ZrO 2 , In 2 O 3 , SnO 2 and HfO 2 ; wherein said intermediate-refractive-index material is SiO 2 , YbF 3 , YF 3 , or a mixture or compound of at least two of SiO 2 , Al 2 O 3 , CeF 3 , NdF 3 , GdF 3 , LaF 3 , YbF 3 and YF 3 ; and wherein said low-refractive-index material is MgF 2 , AlF 3 , or a mixture or compound of at least two of MgF 2 , AlF 3 and SiO 2 .

3. The anti-reflection coating according to claim 1 , wherein said substrate has a refractive index of 1.40-2.10 to said d-line.

4. An optical member comprising the anti-reflection coating recited in claim 1 .

5. An optical equipment comprising the optical member recited in claim 4 .

6. A anti-reflection coating comprising first to seventh layers laminated in this order on an optical substrate with a refractive index of 1.43-1.73 to a helium d-line having a wavelength of 587.56 nm for having reflectance of 0.2% or less to light in a visible wavelength range of 390-720 nm,

said first layer having a refractive index of 1.37-1.56 to said d-line, and an optical thickness of 230-290 nm;

said second layer having a refractive index of 1.85-2.7 to said d-line, and an optical thickness of 20-80 nm;

said third layer having a refractive index of 1.37-1.52 to said d-line, and an optical thickness of 10-60 nm;

said fourth layer having a refractive index of 2.1-2.7 to said d-line, and an optical thickness of 130-220 nm;

said fifth layer having a refractive index of 1.37-1.52 to said d-line, and an optical thickness of 5-40 nm;

said sixth layer having a refractive index of 2.1-2.7 to said d-line, and an optical thickness of 20-90 nm; and

said seventh layer having a refractive index of 1.37-1.4 to said d-line, and an optical thickness of 100-160 nm.

7. The anti-reflection coating according to claim 6 , wherein said seventh layer has a refractive index equal to or less than those of said first, third and fifth layers.

8. The anti-reflection coating according to claim 6 , wherein said first, third and fifth layers are made of MgF 2 or SiO 2 , or a mixture or compound of SiO 2 with Al 2 O 3 , Nb 2 O 5 or TiO 2 ; wherein said second, fourth and sixth layers are made of TiO 2 , Nb 2 O 5 , CeO 2 , Ta 2 O 5 , ZrO 2 , or any of their mixtures or compounds with SiO 2 , and wherein said seventh layer is made of MgF 2 , or a mixture or compound of MgF 2 with SiO 2 , CaF 2 or LiF.

9. An optical member comprising the anti-reflection coating recited in claim 6 .

10. An optical equipment comprising the optical member recited in claim 9 .

11. A anti-reflection coating comprising first to fourteenth layers laminated in this order on an optical substrate having a refractive index of 1.43-2.01 to helium d-line having a wavelength of 587.56 nm,

said first, third, fifth, seventh, ninth, eleventh and thirteenth layers being high-refractive-index layers formed by high-refractive-index materials having refractive indices of 2.201-2.7 to said d-line;

said second, fourth, sixth, eighth, tenth and twelfth layers being intermediate-refractive-index layers formed by an intermediate-refractive-index material having a refractive index of 1.501-1.7 to said d-line;

said fourteenth layer being a low-refractive-index layer formed by a low-refractive-index material having a refractive index of 1.37-1.44 to said d-line;

said first layer having an optical thickness of 5-45 nm;

said second layer having an optical thickness of 15-125 nm;

said third layer having an optical thickness of 40-130 nm;

said fourth layer having an optical thickness of 1-45 nm;

said fifth layer having an optical thickness of 135-175 nm;

said sixth layer having an optical thickness of 20-50 nm;

said seventh layer having an optical thickness of 30-65 nm;

said eighth layer having an optical thickness of 155-180 nm;

said ninth layer having an optical thickness of 10-35 nm;

said tenth layer having an optical thickness of 45-75 nm;

said eleventh layer having an optical thickness of 147-170 nm;

said twelfth layer having an optical thickness of 5-28 nm;

said thirteenth layer having an optical thickness of 55-85 nm; and

said fourteenth layer having an optical thickness of 120-145 nm.

12. The anti-reflection coating according to claim 11 , wherein said optical substrate is made of optical glass, resins or optical crystals.

13. The anti-reflection coating according to claim 11 , wherein said high-refractive-index material is TiO 2 and/or Nb 2 O 5 ; wherein said intermediate-refractive-index material is Al 2 O 3 , a mixture of SiO 2 with TiO 2 , a mixture of SiO 2 with Nb 2 O 5 , a mixture of Al 2 O 3 with TiO 2 , or a mixture of Al 2 O 3 with Nb 2 O 5 ; and wherein said low-refractive-index material is MgF 2 .

14. An optical member comprising the anti-reflection coating recited in claim 11 .

15. An optical equipment comprising the optical member recited in claim 14 .