Dr. Hao Yan Profile

Dr. Hao Yan

at Shanghai Jiao Tong Univ

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Publications (4)

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Proceedings Article | 27 January 2023 Paper

Extended focusing in dual-wavelength digital holography

Sibing Hou, Haiyu Zhang, Bole Ma, Ping Cai, Jiamiao Yang, Hao Yan

Proceedings Volume 12550, 1255010 (2023) https://doi.org/10.1117/12.2667078

KEYWORDS: 3D image reconstruction, Digital holography, Correlation coefficients, 3D image processing, Image sensors, Image restoration, Lasers, CCD image sensors, 3D metrology

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Dual-wavelength digital holography (DH) extends the depth range of measurement, but it faces an issue that it can’t focus the whole extended depth range. In single-wavelength DH, the depth of focus of a correct reconstruction distance is usually sufficient to cover the whole depth range. Therefore, in single-wavelength DH, autofocusing algorithms which can obtain a correct reconstruction distance have been proposed and can solve the issue of focusing the whole depth range. But in dual-wavelength DH and even multi-wavelength DH, the extended depth range of the measurement often spans multiple depths of the focus of the optical system, which means that the depth of focus of a single reconstruction distance is not capable to cover the whole extended depth range, making part of depth out of focus. Therefore, in dual-wavelength DH, only autofocusing is not enough but extended focusing is demanded. However, we lack extended focusing approaches in dual-wavelength DH. Therefore, we propose an extended focusing approach based on correlation coefficient (CC) to focus the whole extended depth range in dual-wavelength DH. The proposed approach includes three steps: (1) dividing the extended depth range by the depth of focus of the system; (2) using the CC-based autofocusing approach to find the correct reconstruction distance of each divided region and reconstructing this region; (3) concatenating reconstructed image of each region and constituting the whole-depth-focused image. Through simulation experiments and practical experiments, the effectiveness and necessity of the proposed approach are verified.

Proceedings Article | 27 January 2023 Paper

3D Measurement of rough objects based on dual wavelength digital holography

Haiyu Zhang, Sibing Hou, Bole Ma, Ping Cai, Jiamiao Yang, Hao Yan

Proceedings Volume 12550, 125500Z (2023) https://doi.org/10.1117/12.2667077

KEYWORDS: Teeth, Digital holography, 3D metrology, Holograms, Shape analysis, Reproducibility

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Traditional topography measurements for rough objects are usually based on point-contact scan. The way of point-contact scan is usually not a high-efficient way to obtain data. Hence, in practice, only a few traces are measured which result in limited data. In order to obtain topography of sufficient amount of data, the demand for rapid noncontact measurement is increasing. In this work, we propose a dual wavelength digital holography (DWDH) measurement system with a synthetic wavelength of 51µm. We apply the DWDH system for 3D measurement of rougher surfaces and objects with a complex and small-size structure to further explore the measurement capability of DWDH. The proposed system enables the possibility to obtain the entire topography with millions of points of a rough surface in a single noncontact measurement. Firstly, we measure a cylinder workpiece of 10mm radius with a large roughness of Ra = 2.6µm which causes severe noise to measurement. The measured radius is 9.8099mm, which indicates a good accuracy. The mean standard deviation of all measured points is 1.08µm, which indicates a good repeatability and good anti-noise capability of the DWDH system. Then the proposed system is applied to measure the tooth surface of a gear of 1mm module and 18 teeth which has a complex and small-size structure. The measured surface shape agrees with the ideal gear tooth surface shape well. And the mean standard deviation of all measured points is 0.94µm, which also verifies its good repeatability. Our work presents the possibility of broader DWDH applications in industrial topography measurements.

Proceedings Article | 13 June 2017 Paper

Multimodal quantitative phase and fluorescence imaging of cell apoptosis

Xinye Fu, Chao Zuo, Hao Yan

Proceedings Volume 10449, 1044920 (2017) https://doi.org/10.1117/12.2270794

KEYWORDS: Luminescence, Phase imaging, Multimodal imaging, Microscopy, Imaging systems, Biomedical optics, 3D image processing, Diffraction, Medical research

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Fluorescence microscopy, utilizing fluorescence labeling, has the capability to observe intercellular changes which transmitted and reflected light microscopy techniques cannot resolve. However, the parts without fluorescence labeling are not imaged. Hence, the processes simultaneously happen in these parts cannot be revealed. Meanwhile, fluorescence imaging is 2D imaging where information in the depth is missing. Therefore the information in labeling parts is also not complete.

On the other hand, quantitative phase imaging is capable to image cells in 3D in real time through phase calculation. However, its resolution is limited by the optical diffraction and cannot observe intercellular changes below 200 nanometers.

In this work, fluorescence imaging and quantitative phase imaging are combined to build a multimodal imaging system. Such system has the capability to simultaneously observe the detailed intercellular phenomenon and 3D cell morphology. In this study the proposed multimodal imaging system is used to observe the cell behavior in the cell apoptosis. The aim is to highlight the limitations of fluorescence microscopy and to point out the advantages of multimodal quantitative phase and fluorescence imaging. The proposed multimodal quantitative phase imaging could be further applied in cell related biomedical research, such as tumor.

Proceedings Article | 19 February 2015 Paper

The phase error reduction using window functions in digital holography

Facai Yan, Hao Yan, Anand Asundi

Proceedings Volume 9449, 94490O (2015) https://doi.org/10.1117/12.2074711

KEYWORDS: Digital holography, Holograms, Charge-coupled devices, Diffraction, 3D image reconstruction, Error analysis, Holography, Image resolution, Optical simulations, Aerospace engineering

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Digital holography (DH) is a 3D imaging technique with a theoretical axial accuracy of better than 1-2 nanome-ters. However, practically, the axial error has been quoted to be tens of nanometers which is much larger than the theoretical value. Previous studies of the axial error mainly focused on the phase error introduced by lens. However, it is found that CCD aperture size is also an important contributors to axial error by our group. It is necessary to investigate the reduction approach of such axial error. The most possible connection between the limited CCD aperture size and the axial error is the diffraction effect. Window functions once have been applied to digital holograms for diffraction suppression and improve the lateral resolution of the intensity image. How-ever, their impacts on phase image and the associated axial dimension measurement are still unknown. In this paper, window functions are applied to digital holograms for phase/axial error reduction. Both simulation and experiment are performed. Moreover, the relation between axial error and window functions is also illustrated by the mathematical formulas derived in the theory. And all the results validate that the window functions can reduce the axial error of digital holography.

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