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Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating
Published on: October 11, 2016
Offset of coherent envelope position due to phase change on reflection
Applied Optics
|March 22, 2008
Summary
Phase changes on reflection impact surface measurements in interferometry. Vertical scanning interferometry shows this shift is predictable for metallic surfaces, preserving fringe shape.
Area of Science:
- Optical Metrology
- Surface Characterization
- Materials Science
Background:
- Interferometric techniques are crucial for precise surface-height measurements.
- Objects made of different materials can exhibit varying phase changes upon reflection, complicating measurements.
- Understanding these phase changes is essential for accurate surface testing.
Purpose of the Study:
- To investigate the influence of phase change on reflection in vertical scanning interferometry (VSI).
- To analyze how different material properties affect surface-height measurements using VSI.
- To quantify the impact of phase shifts on fringe coherence envelopes.
Main Methods:
- Utilized vertical scanning interferometry (VSI) with a broadband light source.
- Conducted theoretical analysis of phase change dispersion on reflection.
- Performed experimental validation using metallic surfaces.
Main Results:
- Demonstrated that phase change on reflection significantly influences surface-height measurements.
- Showed theoretically and experimentally a strong linear dependence of phase change dispersion.
- Observed that fringe coherence envelope shape is preserved but shifted 10-40 nm along the optical axis for metallic surfaces.
Conclusions:
- The dispersion of phase change on reflection is a critical factor in VSI measurements of multi-material objects.
- VSI can accurately measure surface heights even with varying phase changes, provided the shift is accounted for.
- The predictable shift for metallic surfaces allows for improved accuracy in optical metrology.
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