Multi-Incidence Holographic Profilometry for Large Gradient Surfaces with Sub-Micron Focusing Accuracy

Area of Science:

• Optical Metrology
• Surface Characterization
• Digital Holography

Background:

• Reconstructing micro-samples with large discontinuities using digital holography presents challenges.
• Multi-incidence digital holographic profilometry (MIDHP) uses a numerical longitudinal scanning function (LSF) for topography reconstruction.
• Existing MIDHP methods struggle with surfaces exhibiting large gradients due to focusing precision and computational demands.

Purpose of the Study:

• To propose a novel MIDHP method addressing limitations in reconstructing surfaces with large gradients.
• To enhance focusing precision and computational efficiency in MIDHP.
• To enable accurate surface reconstruction for challenging micro-samples.

Main Methods:

• Developed a novel autofocusing algorithm comparing LSF-derived shapes with thin tilted element approximation for submicron resolution focusing.
• Implemented wavefield summation for LSF generation in Fourier space to reduce computational operations and Fourier transforms.
• Validated the enhanced MIDHP method through numerical simulations and experimental measurements.

Main Results:

• The autofocusing algorithm achieves in-focus plane localization with submicron resolution.
• Fourier space LSF generation significantly reduces arithmetic operations and the number of required Fourier transforms, enabling faster processing.
• The novel MIDHP method successfully reconstructs surfaces with large gradients, demonstrating improved functionality.

Conclusions:

• The proposed MIDHP method effectively overcomes limitations in reconstructing surfaces with large gradients and discontinuities.
• The integration of an autofocusing algorithm and Fourier space LSF generation enhances precision and efficiency in digital holographic profilometry.
• This advancement broadens the applicability of MIDHP for detailed surface analysis of micro-samples.