Optical measuring system

• US 20080265150A1
• Filed: 10/29/2007
• Published: 10/30/2008
• Est. Priority Date: 12/12/2003
• Status: Active Grant

• Current Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Original Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Inventors: Holmes, Melanie
• Granted Patent: US 7,847,227 B2
• Time in Patent Office: Days
• US Class Current: 250/252.1
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 27/46 Systems using spatial filters

Abstract

Apparatus and methods are described for measuring amplitude and phase variations in a spatially coherent beam of light. A beam of coherent light is made incident upon a spatial array of phase modulating elements displaying a pixelated first phase distribution. In a measuring region of said spatial array, the phase distribution is changed to a new value while retaining the first phase distribution outside the measuring region, for example by flashing a single pixel. The change in intensity resulting from the change in phase distribution is then determined.

Claims

1-18. -18. (canceled)

19. A method for calibrating an optical system having a Spatial Light Modulator, SLM, the method comprising a comparison of:

a. a phase and/or amplitude distribution of at least one beam incident on the SLM, this phase and/or amplitude distribution measured by means of phase modulating elements on the SLM;

with

b. at least one known feature of the beam.

20. The method of claim 19 wherein:

the optical system comprises a further optical component; and

the method further comprises;

c. adjusting the further optical component to move the position of a feature of the beam incident on the SLM towards a desired position on the SLM.

21. The method of claim 19 further comprising:

c. adjusting the relative position between the SLM and the beam to move the position of a feature of the beam incident on the SLM towards a desired position on the SLM.

22. The method of claim 20 further comprising:

repeating the method steps a., b. and c. until the feature of the beam is incident on the SLM at the desired position.

23. The method of claim 21 further comprising repeating the method steps a., b. and c. until the feature of the beam is incident on the SLM at the desired position.

24. The method of claim 20, wherein the step of adjusting the relative position between the SLM and the beam towards a desired position comprises adjusting the relative transverse position of the SLM with respect to the beam.

25. The method of claim 20, wherein the step of adjusting the relative position between the SLM and beam towards a desired position comprises adjusting the relative longitudinal position of the SLM relative to the beam.

26. The method of claim 25, wherein the beam has a symmetric phase distribution or a symmetric amplitude distribution.

27. The method of claim 26, wherein the beam is Gaussian.

28. The method of claim 27, wherein the beam is asymmetric.

29. The method of claim 19, further comprising assigning or reassigning a block of pixels to the or each beam.

30. The method of claim 19, wherein the optical system further comprises a dispersive element such that different component wavelengths of the beam are incident on different portions of the SLM.

31. The method of claim 19, wherein the known feature of the beam is:

the centre of the beam, an edge of the beam, a phase feature, or an amplitude feature.

32. The method of claim 19, wherein the comparison comprises:

data fitting, centroiding, or feature extraction.

33. Apparatus for characterising a spatially coherent beam of light, comprising:

a LCOS SLM arranged so that a said beam of light can be incident upon it;

means for causing the LCOS SLM to display a first hologram pattern;

means for changing the hologram pattern to a second hologram pattern at a location in said beam where the amplitude and phase of the beam are to be characterised; and

means for measuring an intensity of light to determine the effect of said change of hologram pattern.

34. Apparatus as claimed in claim 33, wherein the means for measuring is disposed in the Fourier plane to detect the Fourier output.

35. Apparatus as claimed in claim 33, further comprising a lens for providing the Fourier output.

36. Apparatus as claimed in claim 33, further comprising a mirror for providing the Fourier output.