Antireflection coating for ultraviolet light at large angles of incidence

• US 20020114068A1
• Filed: 12/12/2001
• Published: 08/22/2002
• Est. Priority Date: 12/15/2000
• Status: Active Grant

• Current Assignee: Carl Zeiss AG (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss Meditec AG (Carl-Zeiss-Stiftung)
• Inventors: Paul, Hans-Jochen, Kuschnereit, Ralf
• Granted Patent: US 6,697,194 B2
• Time in Patent Office: Days
• US Class Current: 359/359
• CPC Class Codes: G02B 1/11 Anti-reflection coatings
• CPC Class Codes: G02B 1/115 Multilayers

Abstract

Antireflection multilayer coatings with only three or four layers are proposed for the production of laser resistant optical components with minimal residual reflection and high transparency for UV light in a wavelength range approx. 150 nm to approx. 250 nm at large angles of incidence in the range of approx. 70° to approx. 80°, particularly in the range between approx. 72° and approx. 76°. For incident p-polarized UV light three-layer systems can be used, in which a layer of low refractive material, in particular magnesium fluoride is arranged between two layers of high refractive material and, in the case of the specified wavelength, of minimally absorbent material, in particular of hafnium oxide or aluminum oxide. For example, this allows a residual reflection of perceptibly less than 1% to be achieved in the case of a wavelength of 248 nm at angles of incidence in the range between approx. 72° and approx. 76°.

Claims

1. Optical component having low reflectance for ultraviolet light of a wavelength in a range between approx. 150 nm and approx. 250 nm at large angles of incidence, the optical component comprising:

a substrate comprising at least one surface;

a multilayer system comprising several stacked layers and applied to the at least one surface of the substrate;

a layer of the multilayer system consisting of either a high refractive dielectric material or a low refractive dielectric material;

the multilayer system consisting of less than five layers.

2. Optical component according to claim 1, wherein the multilayer system consists of three or four layers.

3. Optical component according to claim 1, wherein the multilayer system comprises a first layer arranged adjacent to the substrate, wherein the first layer consists of a high refractive material.

4. Optical component according to claim 1, wherein the layers of the multilayer system are alternately consisting of a high refractive material and a low refractive material.

5. Optical component according to claim 1, wherein at a specified working wavelength the high refractive index material has a refractive index equal to or greater than 1.7.

6. Optical component according to claim 5, wherein the refractive index of the high refractive material is greater then 1.9.

7. Optical component according to claim 1, wherein the high refractive material consists essentially of a metal oxide selected from a group consisting of hafnium oxide, zirconium oxide and aluminum oxide.

8. Optical component according to claim 1, wherein at least one of the materials constituting at least one layer is slightly absorbent at the working wavelength of ultraviolet light.

9. Optical component according to claim 8, wherein an absorption coefficient k of the slightly absorbent material is greater than or equal to approx. 10⁻

6 and less than approximately 0.01.

10. Optical component according to claim 8, wherein an overall thickness of the layers made of slightly absorbent material is less than approximately 100 nm.

11. Optical component according to claim 1, wherein the low refractive material consists essentially of at least one of fluoride and magnesium fluoride.

12. Optical component according to claim 1, wherein the substrate is made of a material selected from the group consisting of glass-like silicon dioxide and fluoride crystal.

13. Optical component according to claim 1, having a residual reflection of less than 1% for ultraviolet light with a wavelength of approximately 248 nm for angles of incidence in a range of 74±

2°

.

14. Optical component according to claim 1, having a residual reflection of less than 2% for ultraviolet light with a wavelength of 193 nm for angles of incidence between approx. 70°

and approx. 75°

.

15. Optical component according to claim 1, wherein an absorption coefficient caused by the multilayer system is less than approximately 1%.

17. Optical component according to claim 16, wherein the absorption coefficient k is less than 0.01.

18. Optical component according to claim 16, wherein the absorption coefficient k is not significantly greater than 0.001.

19. Optical component according to claim 16, wherein the slightly absorbent material is a metal oxide.

20. Optical component according to claim 16, wherein the slightly absorbent material is selected from the group consisting of hafnium oxide and aluminum oxide.

16. Optical component having low reflectance for ultraviolet light of a wavelength in a range between approx. 150 nm and approx. 250 nm at large angles of incidence, the optical component comprising:

a substrate comprising at least one surface;

a multilayer system comprising several stacked layers and applied to the at least one surface of the substrate;

a layer of the multilayer system consisting of either a high refractive dielectric material or a low refractive dielectric material;

the multilayer system comprising at least one layer made of a slightly absorbent material having an absorption coefficient k of more than 10<sup>−

6</sup> at the wavelength of the incident ultraviolet light.

21. Optical component having low reflectance for ultraviolet light of a wavelength in a in a range between approx. 150 nm and approx. 250 nm at large angles of incidence, the optical component comprising:

a substrate comprising at least one surface;

a multilayer system comprising several stacked layers and applied to the at least one surface of the substrate;

a layer of the multilayer system consisting of one of a high refractive dielectric material and a low refractive dielectric material;

the multilayer system comprising a layer of aluminum oxide (Al₂O₃) as the outer layer furthest apart from the substrate.

22. Method for manufacturing an optical component with a low reflectance for ultraviolet light in a wavelength range between approx. 150 nm and approx. 250 nm, the method comprising:

providing a substrate having at least one surface;

depositing on the at least one surface of the substrate an anti-reflective multilayer system by depositing several layers comprising dielectric material, wherein a layer consists of either a high refractive dielectric material or a low refractive material;

wherein said depositing step comprises depositing at least one layer consisting of a slightly absorbent material having an absorption coefficient k of more than 10<sup>−

6</sup> for the incident ultraviolet light.

23. Method for protecting an optical component having an optical coating against the formation of salt deposits under the influence of ultraviolet light in a wavelength range between approximately 150 nm and approximately 250 nm, the method comprising depositing aluminum oxide (Al₂O₃) as the outer layer of the optical coating.