Wavefront-coded phase measuring deflectometry for the all-focused measurement.

Area of Science:

• Optical Engineering
• Metrology
• Surface Characterization

Background:

• Phase measuring deflectometry (PMD) is crucial for complex optical surface metrology.
• Limited camera depth of field causes focus issues, leading to position-angle uncertainty and reduced accuracy in PMD.
• Defocus and other aberrations degrade the quality of captured fringe images, complicating surface reconstruction.

Purpose of the Study:

• To develop a PMD technique robust to defocus and low-order aberrations.
• To enhance measurement accuracy for complex optical surfaces.
• To reduce the stringent focusing requirements in PMD systems.

Main Methods:

• Wavefront coding was employed to modulate the imaging wavefront in the deflectometry system.
• The modulated point spread function was used to deconvolve captured fringe images, correcting for phase errors.
• The enhanced PMD system was tested on a highly curved spherical surface.

Main Results:

• The wavefront coding technique rendered the measurement system insensitive to defocus and aberrations like astigmatism and field curvature.
• Image deconvolution using the modulated point spread function effectively reduced phase errors.
• Measurement accuracy for a highly curved spherical surface was improved by a factor of four.

Conclusions:

• The proposed wavefront coding method significantly enhances the robustness and accuracy of phase measuring deflectometry.
• This technique alleviates the critical focusing requirements, enabling reliable measurement of complex optical surfaces even with defocused images.
• The findings demonstrate a substantial improvement in measurement precision and applicability for advanced optical metrology.