Mirror Support for a Composite Optical Mirror and Method for Its Production

Abstract

A mirror support for an optical mirror and a method for producing an optical mirror are disclosed. In an embodiment a mirror support includes a mirror body comprising a diamond particle reinforced aluminum composite material and a polishing layer arranged on the mirror body, wherein a content of diamond particles in the aluminum composite material is between 5% by mass and 50% by mass inclusive and is selected such that a thermal coefficient of linear expansion of the mirror body is adapted to a thermal coefficient of linear expansion of the polishing layer.

Claims

1-14. (canceled)

15. A mirror support comprising: a mirror body comprising a diamond particle reinforced aluminum composite material; and a polishing layer arranged on the mirror body, wherein a content of diamond particles in the aluminum composite material is between 5% by mass and 50% by mass inclusive and is selected such that a thermal coefficient of linear expansion of the mirror body is adapted to a thermal coefficient of linear expansion of the polishing layer.

16. The mirror support according to claim 15, wherein the mirror body is produced by additive manufacturing.

17. The mirror support according to claim 15, wherein the content of diamond particles in the aluminum composite material is selected such that the thermal coefficient of linear expansion of the mirror body at temperatures of −180° C. to 100° C. is in a range of 3*10.sup.−6/K to 20*10.sup.−6/K.

18. The mirror support according to claim 15, wherein the content of diamond particles in the aluminum composite material is between 10% by mass and 20% by mass inclusive.

19. The mirror support according to claim 15, wherein a cooling structure and/or a supporting structure is integrated into the mirror body.

20. The mirror support according to claim 15, wherein a lightweight structure is integrated into the mirror body.

21. The mirror support according to claim 15, wherein the polishing layer comprises NiP, SiC, Si, SiO.sub.2, Si.sub.3N.sub.4, or ZrO.sub.2.

22. The mirror support according to claim 15, wherein the polishing layer comprises a surface with an RMS roughness of at most 5 nm.

23. A mirror comprising: the mirror support according to claim 15; and at least one reflection layer arranged on the polishing layer.

24. A method for producing a mirror support, the method comprising: producing, by additive manufacturing, a mirror body comprising a diamond particle reinforced aluminum composite material; and applying a polishing layer on the mirror body, wherein a content of diamond particles in the aluminum composite material is between 5% by mass and 50% by mass inclusive and is selected such that a thermal coefficient of linear expansion of the mirror body is adapted to a thermal coefficient of linear expansion of the polishing layer.

25. The method according to claim 24, wherein the additive manufacturing comprises selective laser melting.

26. The method according to claim 24, further comprising integrating, by the additive manufacturing, a supporting structure and/or a cooling structure into the mirror body.

27. The method according to claim 24, further comprising thermally treating the composite material of the mirror body and the polishing layer at a temperature in a range of 130° C. to 200° C.

28. The method according to claim 24, further comprising polishing a surface of the polishing layer so that it comprises an RMS roughness value of less than 5 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The advantageous designs described for the mirror support also apply to the method and vice versa.

[0028] Further details and advantages of the invention can be seen in the following description of FIGS. 1 and 2.

[0029] In the Figures:

[0030] FIG. 1A shows a schematic sectional view of a mirror with the mirror support according to a first exemplary embodiment;

[0031] FIG. 1B shows a section of the mirror with the mirror support according to the first exemplary embodiment; and

[0032] FIG. 2 shows a schematic view of a mirror with the mirror support according to another exemplary embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0033] The optical mirror 4 according to the exemplary embodiment of FIGS. 1A and 1B comprises a mirror support 1 and a reflection layer 5. The mirror support 1 comprises a mirror body 2 and a polishing layer 3, which comprises a NiP alloy. The optical mirror 4 of FIG. 2 comprises an internal cooling structure 6 and a support structure 7.

[0034] In the exemplary embodiment, mirror 4 is an optical mirror with a spherical surface. The implementation of the embodiments is not limited to this mirror form, but is also possible with plane or aspherically curved mirrors or free-form mirrors. The additive manufacturing of the mirror support suggested herein is particularly advantageous for producing the mirror support with a spherically or aspherically curved form or a freeform, since this is very difficult to achieve with conventional manufacturing methods (e.g. casting) due to the mechanical properties of the diamond particle reinforced aluminum composite material. In addition, additive manufacturing allows to reduce the mass of the mirror support, for example by creating recesses or cavities with very thin walls, e.g. 0.1 mm to 1 mm, in the mirror support, which cannot be easily realized with conventional manufacturing processes.

[0035] The mirror body 2 consists of a diamond particle reinforced aluminum composite material with a diamond particle content that causes a coefficient of linear thermal expansion adapted to the NiP polishing layer. The polishing layer 3 consists of a chemically or galvanically produced amorphous nickel-phosphorus alloy with a phosphorus concentration of 10% by mass to 15% by mass (preferably >10.5% by mass, e.g. 12% by mass) and comprises a thickness of about 10 μm to 2000 μm.

[0036] The mirror 4, for example, is produced as follows. First, the mirror body 2 is produced from a diamond particle reinforced aluminum composite material by additive manufacturing (preferably selective laser melting). A homogeneous powder mixture consisting of Al6061 and diamond powder is used. The concrete selection of the content of diamond particles is based on the available material data of the composite material used.

[0037] When using a polishing layer, e.g. PVD-SiC, PVD-Si, CVD-Si, PECVD-SiO.sub.2, PECVD-Si.sub.3N.sub.4, PVD-ZrO.sub.2 or preferably chemically produced NiP, with a layer thickness of <200 μm, a surface of the blank is machined. The blank can be machined ultra-precisely with conventional carbide tools or diamond tools (e.g. PCD tools made of polycrystalline diamond). Since the composite materials used according to embodiments comprise a high proportion of brittle-hard inclusions compared to conventional mirror bodies and are therefore relatively brittle, low cutting depths and low feed rates are preferred for machining.

[0038] By using a polishing layer, e.g. galvanically produced NiP, with a layer thickness of >200 μm, a machining reworking of the blank can be avoided.

[0039] Subsequently, a thermal treatment can be carried out to reduce the stresses introduced. The thermal treatment is preferably carried out for a period of 6 h at 350° C.

[0040] In a further step, the polishing layer 3 is deposited. The deposition of the polishing layer 3 can be achieved in particular by an electroplating or electrochemical process. The deposition preferably includes electroless nickel plating. For this purpose, the surface of the mirror body 2 is first cleaned, activated and then subjected to deposition. After the polishing layer 3 has been applied, a further thermal treatment follows, for example for 6 h at 150° C., in order to reduce layer stresses in the material compound of the mirror support 1. Subsequently, a final polishing can be carried out, producing an RMS surface roughness of less than 5 nm, preferably less than 1 nm.

[0041] To produce a mirror 4 with the mirror support 1, a reflection layer 5 is deposited on the polishing layer 3 in a further step, preferably by physical vapor deposition. The reflection layer 5 can be a single layer or comprise several partial layers. The reflection layer 5 can be a metal layer, for example. Alternatively, the reflection layer 5 can be a multilayer system, for example a dielectric interference layer system or a combination of one or more metal layers with one or more dielectric layers.

[0042] FIG. 2 illustrates another exemplary embodiment of an optical mirror 4. The optical mirror comprises an internal cooling structure 6 and a supporting structure 7. Further designs of the mirror 4 and the mirror support contained therein as well as the method of its manufacture may correspond to the first exemplary embodiment and are therefore not explained again.

[0043] The features of the invention disclosed in the above description, the drawings and the claims may be of importance for the realization of the invention in various forms, either individually or in combination.