Uses of Electromagnetic Interference Patterns

• US 20110157599A1
• Filed: 08/25/2009
• Published: 06/30/2011
• Est. Priority Date: 08/26/2008
• Status: Active Grant

• Current Assignee: University Court of the University of Glasgow (University of Glasgow)
• Original Assignee: University Court of the University of Glasgow (University of Glasgow)
• Inventors: Zhang, Yuan, Docherty, Kevin Edward, Burt, David Paul, Thoms, Stephen, Weaver, Jonathan Mark Ralph, Dobson, Phillip Stephen
• Granted Patent: US 9,618,369 B2
• Time in Patent Office: Days
• US Class Current: 356/496
• CPC Class Codes: G01D 11/00 Component parts of measuring arrangements not specially adapted for a specific variable G01D13/00, G01D15/00 take precedence
• CPC Class Codes: G01D 5/266 by interferometric means G01D5/353 takes precedence
• CPC Class Codes: G01D 5/38 by diffraction gratings
• CPC Class Codes: G01J 2009/0234 Measurement of the fringe pattern
• CPC Class Codes: G01J 9/0246 Measuring optical wavelength
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods
• CPC Class Codes: G03H 1/0005 Adaptation of holography to specific applications holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042

Abstract

Various uses of visible light interference patterns are provided. Suitable interference patterns are those formed by diffraction from patterns of apertures. Typical uses disclosed herein relate to spatial metrology, such as a translational and/or angular position determination system. Further uses include the analysis of properties of the light itself (such as the determination of the wavelength of the electromagnetic radiation). Still further uses include the analysis of one or more properties (e.g. refractive index) of the matter through which the light passes. Part of the interference pattern is captured at a pixellated detector, such as a CCD chip, and the captured pattern compared with a calculated pattern. Very precise measurements of the spacing between maxima is possible, thus allowing very precise measurements of position of the detector in the interference pattern.

Claims

1. A measurement system comprising:

an electromagnetic radiation interference pattern generator for generating an interference pattern including intensity maxima and intensity minima; and

an electromagnetic radiation detector, operable to detect at least a part of the interference pattern produced by said generator, the detector having an array of detection elements arranged to detect a plurality of the intensity maxima and/or intensity minima of the interference pattern substantially simultaneously,

wherein the system is capable of determining a physical property of the system, or a change in a physical property of the system, based on the detected intensity maxima and/or intensity minima.

2. The measurement system according to claim 1 wherein, at the detector, the interference pattern is a two dimensional interference pattern and the detection elements are arranged in a one dimensional array or in a two dimensional array at the detector.

4. The measurement system according to claim 1, further comprising an object whose position is to be measured.

5. The measurement system according to claim 4 wherein the object whose position is to be determined has a fixed spatial relationship with either:

(i) the electromagnetic radiation interference pattern generator, or

(ii) the electromagnetic radiation detector.

6. The measurement system according to claim 5 wherein in use, movement of the object from a first to a second position causes a change of the interference pattern captured at the detector;

and

wherein the object is movable by;

(i) a movement corresponding to translation along at least one of three orthogonal translational axes;

or

(ii) a movement corresponding to rotation about at least one of three orthogonal rotational axes;

said movement of the object, or any combination of said movements providing a variation in the interference pattern or the part of the interference pattern detected by the detector.

15. The measurement system according to claim 1, wherein the interference pattern generator comprises a light source, the electromagnetic radiation provided by the interference pattern generator being spatially coherent;

and

wherein the interference pattern generator comprises an optical element, or a plurality of optical elements, to generate the interference pattern; and

wherein the optical element comprises an arrangement of light-transmitting apertures for the transmission and diffraction of light.

28. The measurement system according to claim 1, wherein the system further comprises a second detector, the second detector being for detecting a different part of the intensity pattern than the first detector.

29. The measurement system according to claim 28 wherein the first detector and the second detector are parts of a single main detector.

32. The measurement system according to claim 1, wherein the system further comprises a second electromagnetic radiation detector, the first and second detectors each being operable to detect a respective part of the interference pattern produced by said generator, and wherein the refractive index of the respective optical paths between the generator and the first and second detectors is deliberately made to be different by a known amount, the patterns detected by the first and second detectors being usable to determine the wavelength of the electromagnetic radiation.

34. The measurement system according to claim 1, further comprising path modification means to provide at least two different path lengths for the electromagnetic radiation from the generator to the detector, so as to provide at least two interference patterns at the detector, corresponding to the at least two different path lengths.

37. The measurement system according to claim 34, wherein the path modification means provides a difference in reflection of the electromagnetic radiation along the respective path lengths.

38. The measurement system according to claim 37 wherein an etalon is provided between the generator and the detector, the different path length being provided in use by different numbers of transits of the electromagnetic radiation across the etalon before reaching the detector.

3. (canceled)

7-14. -14. (canceled)

16-27. -27. (canceled)

30-31. -31. (canceled)

33. (canceled)

35-36. -36. (canceled)

39-43. -43. (canceled)

44. A position determination apparatus comprising a measurement system comprising:

an electromagnetic radiation interference pattern generator for generating an interference pattern including intensity maxima and intensity minima; and

an electromagnetic radiation detector, operable to detect at least a part of the interference pattern produced by said generator, the detector having an array of detection elements arranged to detect a plurality of the intensity maxima and/or intensity minima of the interference pattern substantially simultaneously,

wherein the measurement system is capable of determining a physical property of the system, or a change in a physical property of the system, based on the detected intensity maxima and/or intensity minima.

45. A wavelength determination apparatus comprising a measurement system comprising:

an electromagnetic radiation interference pattern generator for generating an interference pattern including intensity maxima and intensity minima; and

an electromagnetic radiation detector, operable to detect at least a part of the interference pattern produced by said generator, the detector having an array of detection elements arranged to detect a plurality of the intensity maxima and/or intensity minima of the interference pattern substantially simultaneously,

wherein the measurement system is capable of determining a physical property of the system, or a change in a physical property of the system, based on the detected intensity maxima and/or intensity minima.

46. A refractive index determination apparatus comprising a measurement system comprising:

an electromagnetic radiation interference pattern generator for generating an interference pattern including intensity maxima and intensity minima; and

an electromagnetic radiation detector, operable to detect at least a part of the interference pattern produced by said generator, the detector having an array of detection elements arranged to detect a plurality of the intensity maxima and/or intensity minima of the interference pattern substantially simultaneously,

wherein the system is capable of determining a physical property of the system, or a change in a physical property of the system, based on the detected intensity maxima and/or intensity minima.

47-79. -79. (canceled)