A study on carrier phase distortion in phase measuring deflectometry with non-telecentric imaging

Area of Science:

• Optical metrology
• Surface analysis
• Image processing

Background:

• Phase measuring deflectometry (PMD) uses phase-shift techniques to digitize fringe patterns for surface slope analysis.
• Carrier-removal is crucial for evaluating surface slope variations from phase distribution, but nonlinearity in carrier frequency poses challenges.
• Existing methods are limited by system geometries, leading to nonlinear carrier frequency distortions.

Purpose of the Study:

• To investigate nonlinear carrier components in PMD introduced by generalized imaging processes.
• To present the first analytical expression for carrier components in PMD.
• To analyze the impact of system parameters, particularly non-telecentric camera operation, on carrier distortion.

Main Methods:

• Developed an analytical expression for carrier components in PMD.
• Modeled carrier phase distribution using a pinhole perspective model and ray tracing.
• Employed simulation and experimental validation, including reference subtraction techniques.

Main Results:

• The first analytical expression for nonlinear carrier components in PMD was derived.
• Carrier distortion was found to be significantly influenced by non-telecentric camera operation.
• Simulation and experimental results confirmed the analytical model's predictions.

Conclusions:

• The derived analytical form of carrier components allows for detailed analysis of system parameter effects on carrier distortion.
• Elaborate carrier phase removal can overcome restrictions imposed by reflection system geometry.
• This work enhances the accuracy and applicability of PMD for surface metrology.