Non-iterative method and system for phase retrieval

• US 20040052426A1
• Filed: 01/28/2003
• Published: 03/18/2004
• Est. Priority Date: 09/12/2002
• Status: Abandoned Application

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Landesman, Barbara T.
• Application Number:
  US10/353,758
• Publication Number:
  US 20040052426A1
• Time in Patent Office: Days
• US Class Current: 382/255
• CPC Class Codes: G01M 11/00 Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
• CPC Class Codes: G01M 11/0257 by analyzing the image formed by the object to be tested

Abstract

Non-iterative techniques for phase retrieval for estimating errors of an optical system. A method for processing information for an optical system may include capturing a focused image of an object at a focal point (110), capturing a plurality of unfocused images of the object at a plurality of defocus points respectively (110), processing at least information associated with the focused image and the plurality of unfocused images (120 and 130), and determining a wavefront error without an iterative process (140). In addition, a non-iterative system (400) capable of processing image information is also provided.

Claims

1. A method for processing information for an optical system, the method comprising:

capturing a first focused image of a first object at a first focal point;

capturing a plurality of unfocused images of the first object at a plurality of defocus points having a plurality of distances from the first focal point respectively;

processing at least information associated with the first focused image and information associated with the plurality of unfocused images; and

determining a wavefront error using the processing based upon at least the information associated with the first focused image and the information associated with the plurality of unfocused images;

whereupon the processing is free from an iterative process.

2. The method of claim 1 wherein the determining a wavefront error further comprising:

determining image difference based upon at least the information associated with the first focused image and the information associated with the plurality of unfocused images; and

estimating the wavefront error using an analytical process, the analytical process being free from any iterative step using the information associated with the first focused image and the information associated with the plurality of unfocused images.

3. The method of claim 2 wherein the determining image difference further comprising:

obtaining a plurality of differences by subtracting the information associated with the first focused image from the information associated with each of the plurality of unfocused images;

obtaining a plurality of truncated Taylor series expansions by keeping only a number of terms for each of a plurality of Taylor series expansions, the plurality of Taylor series expansions obtained by expanding a plurality of wavefront error exponentials for the first focused image and for each of the plurality of unfocused images;

obtaining a plurality of simplified relations between the wavefront error and the information associated with the first focused image and between the wavefront error and the information associated with each of the plurality of unfocused images; and

obtaining a plurality of simplified differences between the information associated with the first focused image and the information associated with each of the plurality of unfocused images, the information associated with the first focused image having one of the simplified relations, the information associated with each of the plurality of unfocused images having one of the simplified relations.

4. The method of claim 3 wherein the determining image difference further comprising:

calculating a plurality of products by multiplying one of a plurality of summation coefficients to each of the plurality of differences; and

obtaining a sum of image differences by adding the plurality of products.

5. The method of claim 4 wherein the estimating the wavefront error using an analytical process further comprising:

determining the number of the plurality of unfocused images, location of each of the plurality of defocus points, and each of the plurality of summation coefficients, in order to obtaining an analytical relation between the wavefront error and the sum of image differences; and

estimating the wavefront error analytically;

whereupon the estimating is free from an iterative process using the information associated with the first focused image and the information associated with the plurality of unfocused images.

6. The method of claim 5 wherein the number of plurality of unfocused images equals the number of terms.

7. The method of claim 6 wherein the number of plurality of unfocused images equals three.

8. The method of claim 7 wherein a first and a second unfocused images of the plurality of unfocused images are captured at a first and a second defocus points of the plurality of defocus points, the first and the second defocus points having a first and a second distances of the plurality of distances from the first focal point, the first and the second defocus points being on opposite sides of the first focal point.

9. The method of claim 8 wherein a third unfocused image of the plurality of unfocused images is captured at a third defocus point of the plurality of defocus points, the third defocus point located at a third distance of the plurality of distances from the first focal point, the third distance being twice as large as the second distance, the second distance equal to the first distance.

10. The method of claim 9 wherein the plurality of summation coefficients equals −

b, −

3b, and b for the first unfocused image, the second unfocused image, and the third unfocused image respectively, b being a constant.

11. The method of claim 1 wherein the capturing a first focused image comprises:

fine acquisition of the first focused image.

12. The method of claim 11 wherein the capturing a plurality of unfocused images comprises:

fine acquisition of the plurality of unfocused images.

13. The method of claim 1 wherein the optical system is selected from a group consisting of a telescope and a microscope.

14. The method of claim 1 wherein the optical system is an optical system using a phase diversity technique.

15. The method of claim 1 wherein the wavefront error is provided to calibrate the optical system.

16. The method of claim 1 wherein the wavefront error is provided to correct the first focused image.

17. The method of claim 1 wherein the wavefront error is provided to correct a second focused image of the first object captured at a second focal point.

18. The method of claim 1 wherein the wavefront error is provided to correct a second focused image of a second object captured at a second focal point.

19. A system for processing image information, the system comprising:

an optical system;

a control system comprising a computer-readable medium, the computer-readable medium comprising;

one or more instructions for capturing a first focused image of a first object at a first focal point;

one or more instructions for capturing a plurality of unfocused images of the first object at a plurality of defocus points having a plurality of distances from the first focal point respectively;

one or more instructions for processing at least information associated with the first focused image and information associated with the plurality of unfocused images; and

one or more instructions for determining a wavefront error using the processing based upon at least the information associated with the first focused image and the information associated with the plurality of unfocused images;

whereupon the processing is free from an iterative process.

20. The system of claim 19 wherein the determining a wavefront error further comprising:

determining image differences based upon at least the information associated with the first focused image and the information associated with the plurality of unfocused images; and

estimating the wavefront error using an analytical process, the analytical process being free from an iterative step using at least the information associated with the first focused image and the information associated with the plurality of unfocused images.

21. The system of claim 19 wherein the optical system is selected from a group consisting of a telescope and a microscope.

22. The system of claim 19 wherein the optical system is an optical system using a phase diversity technique.

23. The system of claim 19 wherein the control system calibrates the optical system in response to the wavefront error.

24. The system of claim 19 wherein the control system corrects the first focused image in response to the wavefront error.

25. The system of claim 19 wherein the control system corrects a second focused image of the first object captured at a second focal point in response to the wavefront error.

26. The system of claim 19 wherein the control system corrects a second focused image of a second object captured at a second focal point in response to the wavefront error.