Apparatus and method for mechanical phase shifting interferometry

An interferometry system comprising:

• an interferometer which during operation directs different portions of an optical wave front derived from a light source to a pair of surfaces and recombines the different portions to form an optical interference image;
• a phase-shifting component coupled to at least one of the surfaces;
• a multi-element photo-detector positioned to record an interference signal at different locations of the optical interference image;
• and
• an electronic controller coupled to the phase shifting component and the photodetector, wherein the controller is configured to:
• i) cause the photo-detector record to the interference sign at the different locations as the phase shifting component varies the relative position of the two surfaces over a range of positions;
• ii) transform the interference signal for at least one of the locations to produce a spectrum having a peak at a spectral coordinate corresponding to the variation in the relative position of the two surfaces, the spectral coordinate being different from a relative position value;
• iii) identify the spectral coordinate of the peak;
• and iv) for each location, extract the spectral phase of the interference signal at the coordinate of the peak.

An interferometry method comprising:

• forming an optical interference image by combining different portions of an optical wave front reflected from a pair of surfaces;
• recording an interference signal at different locations of the optical interference image in response to varying the relative position of the two surfaces over a range of positions;
• transforming the interference signal for at least one of the locations to produce a spectrum having a peak at a spectral coordinate corresponding to a frequency or wavevector indicative of the variation in the relative position of the two surfaces;
• identifying the spectral coordinate of the peak;
• and
• for each location, extracting the spectral phase of the interference signal at the coordinate of the peak.

An interferometry system comprising:

• an interferometer which during operation directs different portions of an optical wave front derived from a light source to a pair of surfaces and recombines the different portions to form an optical interference image;
• a phase-shifting component coupled to at least one of the surfaces;
• a multi-element photo-detector positioned to record an interference signal at different locations of the optical interference image;
• and
• an electronic controller coupled to the phase shifting component and the photo-detector, wherein the controller is configured to:
• i) cause the photo-detector record to the interference sign at the different locations as the phase shifting component varies the relative position of the two surfaces over a range of positions;
• ii) transform the interference signal for at least one of the locations to produce a spectrum having a peak at a spectral coordinate corresponding to a frequency or wavevector indicative of the variation in the relative position of the two surfaces;
• iii) identify the spectral coordinate of the peak;
• and iv) for each location, extract the spectral phase of the interference signal at the coordinate of the peak.