HS
H. Shangguan
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Digital holography (DH) is a full-field, three-dimensional optical imaging technique for high-speed industrial inspection. By retrieving the complex optical field, DH provides quantitative phase information that enables three-dimensional measurement of surface topography. This thesis is motivated by the demands of advanced semiconductor manufacturing and assembly, where centimeter-scale depth ranges and large field-of-views must be achieved at high throughput. A lensless configuration is used to keep the optical system compact and integration-friendly, while numerical propagation enables refocusing. Within this framework, three key challenges of DH-based metrology are addressed: limited unambiguous depth range due to phase wrapping, pixel-size-limited lateral resolution in lensless DH configurations, and the trade-off between depth range and depth precision.
Industrial samples often exhibit large and abrupt height variations. In singlewavelength DH, the unambiguous depth range of half a wavelength is insufficient to unambiguously determine the height of micrometer to millimeter-scale structures. Chapter 2 describes the development of a dual-wavelength off-axis lensless DH configuration with spatial-frequency multiplexing to enable single-shot acquisition at two discrete wavelengths. By leveraging the beat frequency of the two wavelengths, the system generates a synthetic wavelength, which extends the unambiguous depth range to half the synthetic wavelength. A model for shot-noiselimited phase-precision is derived and experimentally validated. Measurements on calibrated targets and representative industrial samples demonstrate reliable threedimensional reconstruction over extended depth ranges, confirming the suitability of single-shot dual-wavelength DH for high-speed metrology.
When DH is implemented in a lensless configurations, the lateral resolution is constrained by sensor pixel size, which limits the maximum spatial frequencies and thus restricts the detection of fine features such as micro-defects. To overcome this limitation, Chapter 3 introduces an expanding wavefront illumination scheme that increases the available angular spectrum of the object field while maintaining system compactness. A background aberration compensation algorithm is developed to correct global aberrations using locally sampled regions, thereby retaining singleshot operation. By incorporating a tunable external-cavity diode laser, the system achieves a centimeter-scale depth range in combination with micrometer-scale lateral resolution.
Besides a large depth range, industrial metrology also demands high depth precision over the accessible depth span. In conventional dual-wavelength DH, increasing the synthetic wavelength enlarges the unambiguous range but proportionally amplifies phase noise when converted to height, which leads to degraded precision. Chapter 4 addresses this trade-off by developing a multi-wavelength DH technique based on discrete wavelength sampling. In multi-wavelength DH, the surface height is retrieved via multi-point phase fitting in the wavenumber domain, thereby combining Fourier-based coarse depth localization with linear regression. The utilized self-calibration strategy, based on pairwise beat-phase analysis, removes the need for auxiliary high-precision wavelength-monitoring instruments. This approach mitigates noise amplification and improves depth precision over a large depth range, broadening the feasibility of DH for large-scale, high-precision industrial inspection.
In summary, this thesis demonstrates that coordinated advances in optical system design and computational reconstruction can alleviate key limitations of DH in industrial metrology. By extending the depth range, enhancing lateral resolution, and improving depth precision, the proposed methods broaden the applicability of DH while maintaining its intrinsic advantages of full-field imaging and quantitative phase retrieval.
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Industrial samples often exhibit large and abrupt height variations. In singlewavelength DH, the unambiguous depth range of half a wavelength is insufficient to unambiguously determine the height of micrometer to millimeter-scale structures. Chapter 2 describes the development of a dual-wavelength off-axis lensless DH configuration with spatial-frequency multiplexing to enable single-shot acquisition at two discrete wavelengths. By leveraging the beat frequency of the two wavelengths, the system generates a synthetic wavelength, which extends the unambiguous depth range to half the synthetic wavelength. A model for shot-noiselimited phase-precision is derived and experimentally validated. Measurements on calibrated targets and representative industrial samples demonstrate reliable threedimensional reconstruction over extended depth ranges, confirming the suitability of single-shot dual-wavelength DH for high-speed metrology.
When DH is implemented in a lensless configurations, the lateral resolution is constrained by sensor pixel size, which limits the maximum spatial frequencies and thus restricts the detection of fine features such as micro-defects. To overcome this limitation, Chapter 3 introduces an expanding wavefront illumination scheme that increases the available angular spectrum of the object field while maintaining system compactness. A background aberration compensation algorithm is developed to correct global aberrations using locally sampled regions, thereby retaining singleshot operation. By incorporating a tunable external-cavity diode laser, the system achieves a centimeter-scale depth range in combination with micrometer-scale lateral resolution.
Besides a large depth range, industrial metrology also demands high depth precision over the accessible depth span. In conventional dual-wavelength DH, increasing the synthetic wavelength enlarges the unambiguous range but proportionally amplifies phase noise when converted to height, which leads to degraded precision. Chapter 4 addresses this trade-off by developing a multi-wavelength DH technique based on discrete wavelength sampling. In multi-wavelength DH, the surface height is retrieved via multi-point phase fitting in the wavenumber domain, thereby combining Fourier-based coarse depth localization with linear regression. The utilized self-calibration strategy, based on pairwise beat-phase analysis, removes the need for auxiliary high-precision wavelength-monitoring instruments. This approach mitigates noise amplification and improves depth precision over a large depth range, broadening the feasibility of DH for large-scale, high-precision industrial inspection.
In summary, this thesis demonstrates that coordinated advances in optical system design and computational reconstruction can alleviate key limitations of DH in industrial metrology. By extending the depth range, enhancing lateral resolution, and improving depth precision, the proposed methods broaden the applicability of DH while maintaining its intrinsic advantages of full-field imaging and quantitative phase retrieval.
...
Digital holography (DH) is a full-field, three-dimensional optical imaging technique for high-speed industrial inspection. By retrieving the complex optical field, DH provides quantitative phase information that enables three-dimensional measurement of surface topography. This thesis is motivated by the demands of advanced semiconductor manufacturing and assembly, where centimeter-scale depth ranges and large field-of-views must be achieved at high throughput. A lensless configuration is used to keep the optical system compact and integration-friendly, while numerical propagation enables refocusing. Within this framework, three key challenges of DH-based metrology are addressed: limited unambiguous depth range due to phase wrapping, pixel-size-limited lateral resolution in lensless DH configurations, and the trade-off between depth range and depth precision.
Industrial samples often exhibit large and abrupt height variations. In singlewavelength DH, the unambiguous depth range of half a wavelength is insufficient to unambiguously determine the height of micrometer to millimeter-scale structures. Chapter 2 describes the development of a dual-wavelength off-axis lensless DH configuration with spatial-frequency multiplexing to enable single-shot acquisition at two discrete wavelengths. By leveraging the beat frequency of the two wavelengths, the system generates a synthetic wavelength, which extends the unambiguous depth range to half the synthetic wavelength. A model for shot-noiselimited phase-precision is derived and experimentally validated. Measurements on calibrated targets and representative industrial samples demonstrate reliable threedimensional reconstruction over extended depth ranges, confirming the suitability of single-shot dual-wavelength DH for high-speed metrology.
When DH is implemented in a lensless configurations, the lateral resolution is constrained by sensor pixel size, which limits the maximum spatial frequencies and thus restricts the detection of fine features such as micro-defects. To overcome this limitation, Chapter 3 introduces an expanding wavefront illumination scheme that increases the available angular spectrum of the object field while maintaining system compactness. A background aberration compensation algorithm is developed to correct global aberrations using locally sampled regions, thereby retaining singleshot operation. By incorporating a tunable external-cavity diode laser, the system achieves a centimeter-scale depth range in combination with micrometer-scale lateral resolution.
Besides a large depth range, industrial metrology also demands high depth precision over the accessible depth span. In conventional dual-wavelength DH, increasing the synthetic wavelength enlarges the unambiguous range but proportionally amplifies phase noise when converted to height, which leads to degraded precision. Chapter 4 addresses this trade-off by developing a multi-wavelength DH technique based on discrete wavelength sampling. In multi-wavelength DH, the surface height is retrieved via multi-point phase fitting in the wavenumber domain, thereby combining Fourier-based coarse depth localization with linear regression. The utilized self-calibration strategy, based on pairwise beat-phase analysis, removes the need for auxiliary high-precision wavelength-monitoring instruments. This approach mitigates noise amplification and improves depth precision over a large depth range, broadening the feasibility of DH for large-scale, high-precision industrial inspection.
In summary, this thesis demonstrates that coordinated advances in optical system design and computational reconstruction can alleviate key limitations of DH in industrial metrology. By extending the depth range, enhancing lateral resolution, and improving depth precision, the proposed methods broaden the applicability of DH while maintaining its intrinsic advantages of full-field imaging and quantitative phase retrieval.
Industrial samples often exhibit large and abrupt height variations. In singlewavelength DH, the unambiguous depth range of half a wavelength is insufficient to unambiguously determine the height of micrometer to millimeter-scale structures. Chapter 2 describes the development of a dual-wavelength off-axis lensless DH configuration with spatial-frequency multiplexing to enable single-shot acquisition at two discrete wavelengths. By leveraging the beat frequency of the two wavelengths, the system generates a synthetic wavelength, which extends the unambiguous depth range to half the synthetic wavelength. A model for shot-noiselimited phase-precision is derived and experimentally validated. Measurements on calibrated targets and representative industrial samples demonstrate reliable threedimensional reconstruction over extended depth ranges, confirming the suitability of single-shot dual-wavelength DH for high-speed metrology.
When DH is implemented in a lensless configurations, the lateral resolution is constrained by sensor pixel size, which limits the maximum spatial frequencies and thus restricts the detection of fine features such as micro-defects. To overcome this limitation, Chapter 3 introduces an expanding wavefront illumination scheme that increases the available angular spectrum of the object field while maintaining system compactness. A background aberration compensation algorithm is developed to correct global aberrations using locally sampled regions, thereby retaining singleshot operation. By incorporating a tunable external-cavity diode laser, the system achieves a centimeter-scale depth range in combination with micrometer-scale lateral resolution.
Besides a large depth range, industrial metrology also demands high depth precision over the accessible depth span. In conventional dual-wavelength DH, increasing the synthetic wavelength enlarges the unambiguous range but proportionally amplifies phase noise when converted to height, which leads to degraded precision. Chapter 4 addresses this trade-off by developing a multi-wavelength DH technique based on discrete wavelength sampling. In multi-wavelength DH, the surface height is retrieved via multi-point phase fitting in the wavenumber domain, thereby combining Fourier-based coarse depth localization with linear regression. The utilized self-calibration strategy, based on pairwise beat-phase analysis, removes the need for auxiliary high-precision wavelength-monitoring instruments. This approach mitigates noise amplification and improves depth precision over a large depth range, broadening the feasibility of DH for large-scale, high-precision industrial inspection.
In summary, this thesis demonstrates that coordinated advances in optical system design and computational reconstruction can alleviate key limitations of DH in industrial metrology. By extending the depth range, enhancing lateral resolution, and improving depth precision, the proposed methods broaden the applicability of DH while maintaining its intrinsic advantages of full-field imaging and quantitative phase retrieval.
Lensless single-shot dual-wavelength digital holography is resolution limited by the pixel-size of the camera and often has an insufficient depth range. We present a novel dual-wavelength holographic configuration with expanding wavefront illumination that breaks the pixel-limited resolution barrier and achieves diffraction-limited spatial resolution. By implementing expanding wavefront illumination with dual-wavelength digital holography based on a wavelength-tunable laser, we achieve a high-resolution centimeter-scale depth range. A quantitative precision analysis demonstrates that single-shot acquisition reaches the shot-noise-limited depth detection. The proposed holographic scheme provides a robust 3D optical inspection solution for high-throughput, micro-scale resolution industrial inline metrology.
...
Lensless single-shot dual-wavelength digital holography is resolution limited by the pixel-size of the camera and often has an insufficient depth range. We present a novel dual-wavelength holographic configuration with expanding wavefront illumination that breaks the pixel-limited resolution barrier and achieves diffraction-limited spatial resolution. By implementing expanding wavefront illumination with dual-wavelength digital holography based on a wavelength-tunable laser, we achieve a high-resolution centimeter-scale depth range. A quantitative precision analysis demonstrates that single-shot acquisition reaches the shot-noise-limited depth detection. The proposed holographic scheme provides a robust 3D optical inspection solution for high-throughput, micro-scale resolution industrial inline metrology.
We demonstrate lensless single-shot dual-wavelength digital holography for high-speed 3D imaging in industrial inspection. Single-shot measurement is realized by combining off-axis digital holography and spatial frequency multiplexing of the two wavelengths on the detector. The system has 9.1 µm lateral resolution and a 50 µm unambiguous depth range. We determine the theoretical accuracy of off-axis dual-wavelength phase reconstruction for the case of shot-noise-limited detection. Experimental results show good agreement with the proposed model. The system is applied to industrial metrology of calibrated test samples and chip manufacturing.
...
We demonstrate lensless single-shot dual-wavelength digital holography for high-speed 3D imaging in industrial inspection. Single-shot measurement is realized by combining off-axis digital holography and spatial frequency multiplexing of the two wavelengths on the detector. The system has 9.1 µm lateral resolution and a 50 µm unambiguous depth range. We determine the theoretical accuracy of off-axis dual-wavelength phase reconstruction for the case of shot-noise-limited detection. Experimental results show good agreement with the proposed model. The system is applied to industrial metrology of calibrated test samples and chip manufacturing.