Apparatus and method for measurement of fields of backscattered and forward scattered/reflected beams by an object in interferometry

An interferometry system for making interferometric measurements of an object, said system comprising:

• a source assembly that generates an array of input beams;
• a detector assembly that includes an array of detector elements;
• and
• an interferometer that includes a source imaging system that focuses the array of input beams onto an array of spots on or in the object and an object imaging system that images the array of spots onto the array of detector elements as an array of interference beams, said object imaging system combining light coming from each spot of the array of spots with a corresponding reference beam to produce a corresponding interference beam of the array of interference beams,
• wherein the source imaging system is characterized by a first aperture stop that defines a first aperture, said source imaging system including a first phase shifter that introduces a first phase shift in light passing through a first region of the first aperture relative to light passing through a second region of the first aperture, said second region of the first aperture being the region of the first aperture that is outside of the first region of the first aperture, and
• wherein the object imaging system is characterized by a second aperture stop that defines a second aperture, said object imaging system including a second phase shifter that introduces a second phase shift in light passing through a first region of the second aperture relative to light passing through a second region of the second aperture, said second region of the second aperture being the region of the second aperture that is outside of the first region of the second aperture.

A method of making interferometric measurements of an object, said method comprising:

• generating a input beam;
• deriving first and second measurement beams from the input beam;
• focusing the first and second measurement beams onto a spot on or in the object to produce a first return measurement beam and a second return measurement beam, said first return measurement beam resulting from forward reflection and/or forward scattering of the first measurement beam by the object plus backscattering of the second measurement beam by the object, said second measurement beam resulting from forward reflection and/or forward scattering of the second measurement beam by the object plus backscattering of the first measurement beam by the object;
• interfering the first and second return measurement beams with a reference beam to produce an interference beam;
• focusing the interference beam onto the detector element to produce an interference signal;
• and
• establishing measurement conditions by shifting the first measurement beam in phase relative to the second measurement beam by a first amount and by shifting the second return measurement beam in phase relative to the first return measurement beam by a second amount.