Digital holography free of 2π ambiguity, using coherence modulation

Area of Science:

• * Optics
• * Metrology
• * Digital Holography

Background:

• * Low-coherence digital holography is a powerful technique for 3D profilometry.
• * Phase ambiguity (2π ambiguity) is a common challenge in phase-based measurement methods.
• * Existing methods for phase ambiguity resolution often involve complex numerical processing or dual-wavelength approaches.

Purpose of the Study:

• * To introduce a novel quantitative measurement method for low-coherence digital holography.
• * To extend the axial measurement range by effectively removing phase ambiguity.
• * To demonstrate an accurate and simpler approach to phase ambiguity resolution.

Main Methods:

• * Developed a quantitative measurement method utilizing the characteristics of the light source.
• * Obtained degree of coherence and phase values based on light source properties.
• * Employed three phase-shifting holograms with described mathematical procedures.
• * Leveraged the modulation of coherence degree with optical path difference to resolve phase ambiguity.

Main Results:

• * Successfully obtained degree of coherence and phase values.
• * Demonstrated the removal of 2π phase ambiguity without numerical or dual-wavelength methods.
• * Achieved accurate measurements of a sample with a high step.
• * Validated the effectiveness of the proposed method through experimental results.

Conclusions:

• * The presented method provides an effective way to resolve phase ambiguity in low-coherence digital holography.
• * This technique extends the axial measurement range and simplifies the measurement process.
• * The method offers accurate quantitative measurements, particularly for samples with significant height variations.