Dual-wavelength digital holography: single-shot shape evaluation using speckle displacements and regularization

Area of Science:

• Optical Metrology
• 3D Shape Analysis
• Holographic Interferometry

Background:

• Accurate 3D shape evaluation of free-form objects is crucial in manufacturing and quality control.
• Comparing measured shapes to Computer-Aided Design (CAD) models requires high precision and robust methods.

Purpose of the Study:

• To develop and validate a high-precision method for evaluating the shape of free-form objects by comparing them to CAD models.
• To demonstrate the efficacy of dual-wavelength holography for quantitative surface metrology.

Main Methods:

• Utilizing single-shot dual-wavelength holography with a synthetic wavelength of 1.4 mm.
• Numerical propagation of holograms and correlation to obtain speckle displacement vector fields.
• Extracting surface gradient fields and aligning them to CAD models using the iterative closest point (ICP) algorithm and regularization.

Main Results:

• A method for extracting surface gradients from speckle displacements was established.
• The ICP algorithm and regularization enabled alignment of measured data to CAD models.
• High-precision shape evaluation was achieved, with standard deviations between 7 and 19 μm relative to the CAD model, depending on surface slope.

Conclusions:

• Dual-wavelength holography provides a viable and precise method for 3D shape evaluation against CAD models.
• The developed technique offers high accuracy for metrology applications, with potential for further optimization.
• The phase difference field effectively quantifies deviations between the measured shape and the digital model.