Extended-Aperture Shape Measurements Using Spatially Partially Coherent Illumination (ExASPICE)

Area of Science:

• Optical Metrology
• 3D Imaging
• Micro-part Measurement

Background:

• SPICE profilometry uses LED illumination and speckle contrast for 3D shape measurement.
• Existing SPICE methods offer speed and robustness but are limited by small illumination apertures affecting axial resolution.
• Confocal and white light interferometry are alternatives but can be slower or less robust.

Purpose of the Study:

• To overcome the aperture angle limitation in SPICE profilometry.
• To improve the axial scan resolution and measurement accuracy of SPICE.
• To present a novel multi-directional LED illumination method for SPICE.

Main Methods:

• Illuminating the object from different directions using multiple independent LED sources.
• Utilizing an electrically tunable lens in a 4f-configuration for fast depth scanning.
• Evaluating speckle contrast for depth discrimination with spatially partially coherent illumination.

Main Results:

• Reduced the full width at half maximum of the contrast envelope by one-eighth.
• Achieved a twofold improvement in measurement accuracy compared to standard SPICE.
• Successfully demonstrated shape measurements of various metal objects.

Conclusions:

• The proposed multi-directional LED illumination effectively overcomes SPICE's aperture limitation.
• This method significantly enhances measurement accuracy and axial resolution in 3D profilometry.
• The technique offers a fast, eye-safe, and robust solution for micro-part 3D shape measurement.