Holographic Interferometer Superpixel Phase Extraction for Fast Scanning
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Solution Overview
Problem
Existing holographic interferometry methods are too slow for lateral scanning of objects, especially in applications like wafer inspection, due to the need for multiple image acquisitions and phase unwrapping, and they struggle with non-uniform interference line density across the field of view.
Innovation Solution
A holographic interferometer with identical optical paths for object and reference beams, using multiple angle split beams from a single light source, and analyzing images with super pixels to extract phase information, eliminating the need for multiple wavelength light sources and reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple image acquisitions and phase scanning mechanism are used, then phase and amplitude information can be separated, but the scanning speed becomes too slow for lateral scanning applications
Solution Approach 1:
The patent extracts phase information directly from a single holographic image by introducing a non-zero angle between object and reference beams, eliminating the need for multiple acquisitions and phase scanning mechanisms. This allows phase measurement to be obtained immediately from the interference pattern without requiring sequential scanning.
Solution Approach 2:
The patent applies preliminary tilting of the reference beam to create a carrier frequency in the interference pattern before image acquisition. This pre-established angular offset enables direct phase extraction from the spatial frequency distribution of the interference lines, avoiding the need for post-acquisition phase scanning.
2Productivity
If a non-zero angle is introduced between object and reference beams for fast scanning, then single image phase extraction becomes possible, but interference line density becomes non-uniform across the field of view
Solution Approach 1:
The patent applies local quality by using super pixels - small local regions in the image where phase analysis is performed independently. Each super pixel captures a localized interference pattern with relatively uniform density, and phase information is extracted from these local regions rather than requiring uniform density across the entire field of view.
Solution Approach 2:
The patent transitions from analyzing the entire 2D image at once to analyzing local 2D regions (super pixels) independently. This dimensional decomposition allows phase extraction from localized areas where interference line density is sufficient, bypassing the problem of non-uniform density across the full field of view.
3Measurement precision
If multiple wavelength light sources are used to achieve uniform interference line density, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent creates multiple effective wavelengths through spatial frequency manipulation of a single wavelength light source. By analyzing different spatial frequency components of the interference pattern (via Fourier transform of super pixels), the system synthesizes phase information equivalent to what would be obtained from multiple wavelength sources, but using only a single laser.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables fast lateral scanning and accurate phase measurement with uniform interference line density, increasing throughput and reducing costs by using a single light source and minimizing computational expense.
Implementation Method 1
an interference pattern caused by the reference and object beams
Data Source
Figure 1
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Figure 4~5
AI summary
A holographic interferometer, comprising: at least one imaging device capturing an interference pattern created by at least two light beams; and at least one aperture located in an optical path of at least one light beam of the at least two light beams; wherein the at least one aperture is located away from an axis of the at least one light beam, thus transmitting a subset of the at least one light beam collected at an angle range.