Diffractive null corrector employing a spatial light modulator

• US 20080079950A1
• Filed: 10/02/2006
• Published: 04/03/2008
• Est. Priority Date: 10/02/2006
• Status: Active Grant

• Current Assignee: ASML Holding NV
• Original Assignee: ASML Holding NV
• Inventors: Harned, Robert D., Harned, Nora-Jean
• Granted Patent: US 7,443,514 B2
• Time in Patent Office: Days
• US Class Current: 356/512
• CPC Class Codes: G01B 11/2441 using interferometry
• CPC Class Codes: G01J 2009/0223 Common path interferometry; Point diffraction interferometry
• CPC Class Codes: G01M 11/005 Testing of reflective surfaces, e.g. mirrors
• CPC Class Codes: G01M 11/025 by determining the shape of the object to be tested measuring contours or curvatures by optical means G01B11/24
• CPC Class Codes: G01M 11/0264 by using targets or reference patterns
• CPC Class Codes: G01M 11/0271 by using interferometric methods

Abstract

The present invention is directed to a system and method for using a spatial light modulator (SLM) to perform a null test of an (aspheric) optical surface. In an embodiment, such a system includes an interferometer, an optical element, and an SLM. The interferometer provides electromagnetic radiation. The optical element conditions the electromagnetic radiation to provide a first beam of radiation and a second beam of radiation. The SLM shapes a wavefront of the first beam of radiation resulting in a shaped wavefront corresponding to an optical surface. The shaped wavefront is incident on and conditioned by the optical surface. The shape of the optical surface is analyzed based on a fringe pattern resulting from interference between the shaped wavefront mapped by the optical surface and the second beam of radiation. The system may also include an optical design module that converts a null corrector design corresponding to the optical surface into instructions for the SLM.

Claims

1. A system for testing an optical surface, comprising:

an interferometer that provides electromagnetic radiation;

an optical element that conditions the electromagnetic radiation to provide a first beam of radiation and a second beam of radiation; and

a spatial light modulator (SLM) that shapes a wavefront of the first beam of radiation resulting in a shaped wavefront corresponding to an optical surface, wherein the shaped wavefront is incident on and conditioned by the optical surface, and wherein the shape of the optical surface is analyzed based on a fringe pattern resulting from interference between the shaped wavefront mapped by the optical surface and the second beam of radiation.

2. The system of claim 1, further comprising:

an optical design module that converts a null corrector design corresponding to the optical surface into instructions for the SLM.

3. The system of claim 1, wherein the optical element is a focusing optic that focuses the first beam of radiation on the SLM.

4. The system of claim 1, further comprising:

an analysis module that analyzes the fringe pattern.

5. The system of claim 1, further comprising:

an auxiliary optic coupled with the optical surface, wherein the auxiliary optic also conditions the shaped wavefront.

6. The system of claim 5, wherein prior to shaping the wavefront of the first beam of radiation, the SLM shapes a wavefront of light to align the auxiliary optic.

7. The system of claim 1, wherein the SLM attenuates the shaped wavefront conditioned by the optical surface to compensate for low fringe contrast in the fringe pattern.

8. The system of claim 1, wherein the SLM shapes a wavefront of the first beam of radiation to compensate for errors in the interferometer resulting in a shaped wavefront corresponding to an optical surface.

9. The system of claim 1, wherein the optical surface is a concave surface, a convex surface, a reflective surface, or a transmissive surface.

10. The system of claim 1, wherein the interferometer comprises one of a Fizeau interferometer, a Twyman-Green interferometer, or a Mach-Zehnder interferometer.

11. A method for testing an optical surface, comprising:

providing a first beam of radiation and a second beam of radiation;

shaping a wavefront of the first beam of radiation with a spatial light modulator (SLM) resulting in a shaped wavefront corresponding to the optical surface;

conditioning the shaped wavefront with the optical surface;

producing a fringe pattern based on interference between the shaped wavefront conditioned by the optical surface and the second beam of radiation; and

analyzing the shape of the optical surface based on the fringe pattern.

12. The method of claim 11, further comprising:

converting a null corrector design corresponding to the optical surface into instructions for the SLM.

13. The method of claim 11, further comprising:

focusing the first beam of radiation on the SLM with a focusing optic.

14. The method of claim 11, further comprising:

analyzing the shape of the optical surface based on the fringe pattern by using an analysis module.

15. The method of claim 11, further comprising:

conditioning the shaped wavefront with an auxiliary optic.

16. The method of claim 15, wherein prior to shaping a wavefront of the first beam of radiation, the method comprises:

aligning the auxiliary optic using the SLM.

17. The method of claim 11, further comprising:

attenuating the shaped wavefront conditioned by the optical surface to compensate for low fringe contrast in the fringe pattern.

18. The method of claim 11, wherein the shaping step comprises:

shaping a wavefront of the first beam of radiation with a spatial light modulator (SLM) to compensate for errors in the first beam of radiation resulting in a shaped wavefront corresponding to the optical surface.

19. The method of claim 11, wherein the shaping step comprises:

shaping a wavefront of the first beam of radiation with a spatial light modulator (SLM) that results in a shaped wavefront corresponding to an optical surface, wherein the optical surface is a concave surface, a convex surface, a reflective surface, or a transmissive surface.

20. A system for testing an optical surface, comprising:

an interferometer that provides a first beam of radiation and a second beam of radiation; and

a spatial light modulator (SLM) that shapes a wavefront of the first beam of radiation resulting in a shaped wavefront corresponding to an optical surface, wherein the shaped wavefront is incident on and conditioned by the optical surface, and wherein the shape of the optical surface is analyzed based on a fringe pattern resulting from interference between the shaped wavefront mapped by the optical surface and the second beam of radiation.