Methods and apparatus for splitting, imaging, and measuring wavefronts in interferometry

Claims

What is claimed is:

1. Apparatus for splitting a wavefront, said apparatus comprising:

a wavefront-splitting element for:

receiving a wavefront including a reference wavefront and an object wavefront said reference wavefront and said object wavefront being orthogonally polarized;

splitting said wavefront into a plurality of sub-wavefronts such that each of said said sub-wavefronts is substantially contiguous with at least one other said sub-wavefront, wavefront-splitting element splitting said wavefront such that each of said sub-wavefront includes said reference wavefront and said object wavefront;

providing said plurality of sub-wavefronts;

a phase-shifting interference element for:

receiving said plurality of sub-wavefronts;

discretely shifting the relative phase between said reference wavefront and said object wavefront of said sub-wavefronts to yield a respective plurality of phase-shifted sub-wavefronts;

interfering said reference and said object wavefronts of said phase-shifted sub-wavefronts to yield a respective plurality of phase-shifted interferograms, said phase-shifted interferograms; and

providing said plurality of phase-shifted interferograms; and

a sensing element for receiving said phase-shifted interferograms from said phase-shifting interference element.

2. Apparatus for splitting a wavefront, said apparatus comprising:

a wavefront-splitting element for;

receiving a wavefront including a reference wavefront and an object wavefront, said reference wavefront and said object wavefront being orthogonally polarized;

splitting said wavefront into a plurality of sub-wavefronts such that each of said sub-wavefronts is substantially contiguous with at least one other said sub-wavefront, said wavefront-splitting element splitting said wavefront such that each of said sub-wavefront includes said reference wavefront and said object wavefront;

providing said plurality of sub-wavefronts;

a phase-shifting interference element having a plurality of sections, each of said sections for:

receiving a respective one of said sub-wavefronts;

shifting the relative phase between said reference wavefront and said object wavefront of said sub-wavefronts to yield a respective phase-shifted sub-wavefront;

interfering said reference and said object wavefronts of said respective phase-shifted sub-wavefront to yield a respective phase-shifted interferogram; and

providing said respective phase-shifted interferograms; and

a sensing element for receiving said phase-shifted interferograms from said phase-shifting interference element.

3. Apparatus for measuring a spatial phase of wavefronts, said apparatus comprising:

a wavefront-splitting, element for:

receiving a combined wavefront including a reference wavefront and an object wavefront, said reference wavefront and said object wavefront being orthogonally polarized;

splitting said combined wavefront into a plurality of sub-wavefronts such that each of said sub-wavefronts is substantially contiguous with at least one other said sub-wavefront, each of said sub-wavefronts including said object wavefront and said reference wavefront, each of said sub-wavefronts having a phase;

providing said plurality of sub-wavefronts;

a phase-shifting interference element including a plurality of sections, each of said sections for:

receiving a respective one of said sub-wavefronts;

shifting the relative phase between said reference and said object wavefronts of said sub-wavefront received thereby to yield a phase-shifted sub-wavefront;

interfering said reference and said object wavefronts of said phase-shifted sub-wavefront to yield a phase-shifted interferogram;

providing said phase-shifted interferogram; and

a sensing element having a pixelated surface for receiving said phase-shifted interferogram from each of said sections of said phase-shifting element.

4. Apparatus as claimed in claim 3 wherein each of said sections of said phase-interference shifting element shifts the relative phase of said sub-wavefront received thereby by a factor of a predetermined amount substantially equal to the quotient of 360 degrees and the number of sub-wavefronts in said plurality of sub-wavefronts.

5. Apparatus as claimed in claim 4 wherein said wavefront-splitting element splits said combined wavefront into four sub-wavefronts.

6. Apparatus as claimed in claim 3 wherein said sensing element is positioned at or near said phase-shifting interference element.

7. Apparatus as claimed in claim 3 wherein said combined wavefront is coherent light.

8. Apparatus as claimed in claim 3 wherein said wavefront-splitting element includes a diffractive optical element.

9. Apparatus as claimed in claim 3 wherein said sensing element includes a charged coupled device.

10. Apparatus as claimed in claim 3 wherein said phase-shifting interference element includes:

a first plate including a quarter-wave plate and a blank plate, said quarter-wave plate for shifting said reference and object wavefronts by 90.degree., said blank plate for shifting said reference and object wavefronts by 020 ; and

a second plate including a first polarizing plate and a second polarizing plate, said first polarizing plate for interfering in-phase components of said reference and object wavefronts, said second polarizing plate for interfering out-of-phase components of said reference and object wavefronts.

11. Apparatus as claimed in claim 10 wherein:

one of said sections is defined by said blank plate and said first polarizing plate;

one of said sections is defined by said quarter-wave plate and said first polarizing plate;

one of said sections is defined by said blank plate and said second polarizing plate; and

one of said sections is defined by said quarter-wave plate and said second polarizing plate.

12. Apparatus as claimed in claim 11 wherein said first plate and said second plate are disposed in a parallel relationship.

13. Apparatus as claimed in claim 12 wherein said first plate and said second plate abut.

14. Apparatus for measuring spatial phase of wavefronts, said apparatus comprising:

a transmit portion for providing a reference wavefront and an object wavefront, said object wavefront acting upon an object;

an image portion including:

a combining element for receiving said reference wavefront from said transmit portion and said object wavefront from the object and for combining said reference and object wavefronts into a combined wavefront, said object wavefront and said reference wavefront being orthogonally polarized with respect to each other;

a wavefront-splitting element for splitting said combined wavefront into four sub-wavefronts such that each of said sub-wavefronts is substantially contiguous with at least one other said sub-wavefront, each of said sub-wavefronts having a phase;

a phase-shifting interference element including four sections, said phase-shifting interference element being disposed with respect to said wavefront-splitting element so that said sub-wavefronts are respectively incident on said sections, each of said sections for shifting the relative phase of and for interfering said reference and object wavefronts of said sub-wavefront incident thereon to yield a phase-shifted interferogram; and

an imaging element for receiving said phase-shifted interferograms from said sections of said phase-shifting interference element, said imaging element being disposed with respect to said phase-retardant plate so that said phase-shifted interferograms are imaged substantially simultaneously.

15. Apparatus as claimed in claim 14 wherein said transmit portion includes a laser for providing coherent light.

16. Apparatus as claimed in claim 15 wherein said transmit portion further includes a beam splitting for splitting said coherent light into said reference wavefront and said object wavefront.

17. Apparatus as claimed in claim 14 wherein said wavefront-splitting element includes a diffractive optical element.

18. Apparatus as claimed in claim 14 wherein said imaging element includes a charge coupled device.

19. Apparatus as claimed in claim 14 further comprising a computer connected to said imaging device for processing said phase-shifted interferograms.

20. A method for measuring spatial phase of wavefronts, said method comprising the steps of:

splitting a combined wavefront into four sub-wavefronts such that each of said sub-wavefronts is substantially contiguous with at least one other said sub-wavefront, said combined wavefront including a reference wavefront and an object wavefront orthogonally polarized with respect to each other, each of said sub-wavefronts having a phase;

shifting the relative phase of said reference and object wavefronts of each said sub-wavefront;

interfering said reference and object wavefronts of each said sub-wavefront; and

imaging each of said sub-wavefronts.

21. A method as claimed in claim 20 wherein said imaging step comprises the step of:

imaging each of said sub-wavefronts substantially contiguously on a single sensing element.

22. A method as claimed in claim 21 wherein said imaging step comprises the step of:

imaging each of said sub-wavefronts on multiple imaging elements configured to function as a single element.

23. A method as claimed in claim 20 further comprising the step of:

generating coherent light;

splitting said coherent light into said reference wavefront and said object wavefront; and

transmitting said object wavefront to an object under measure.

24. A method as claimed in claim 20 wherein said shifting step comprises the step of:

discretely shifting the relative phase of said reference and object wavefronts of each said sub-wavefront.

25. A method for measuring a profile of an object, said method comprising the steps of:

generating a plurality of wavefronts each having a unique wavelength, each said wavefront includes a reference wavefront and an object wavefront;

transmitting said object wavefront of each said wavefront to an object;

combining each said object wavefront from the object with said reference wavefront of same wavelength to yield a respective plurality combined wavefronts;

splitting said combined wavefronts into a respective sets of sub-wavefronts such that each said sub-wavefront is substantially contiguous with at least one other said sub-wavefront of the same set, each said sub-wavefront includes said reference wavefront and said object wavefront;

imaging said sets of sub-wavefronts; and

determining distance to the object based on said imaged sets of sub-wavefronts.

26. A method as claimed in claim 25 wherein said splitting step comprises the steps of:

shifting the relative phase between said reference wavefront and said object wavefront of said sub-wavefronts to yield a respective plurality of phase-shifted sub-wavefronts; and

interfering said reference and said object wavefronts of said phase-shifted sub-wavefronts to yield a respective plurality of phase-shifted interferograms; wherein:

said imaging step comprises the step of imaging said phase-shifted interferograms; and

said determining step comprises the step of determining distance to the object based on said phase-shifted interferograms.

27. Apparatus for measuring a profile of an object, said apparatus comprising:

a plurality of wavefronts each having a wavelength, each said wavefront includes a reference wavefront and an object wavefront, said object wavefront of e