Spatial multiplexing digital holography for speckle noise reduction in single-shot holographic two-wavelength contouring

Agour, Mostafa; Klattenhoff, Reiner; Falldorf, Claas; Bergmann, Ralf B.

doi:10.1117/1.oe.56.12.124101

Cited by 5 publications

(10 citation statements)

References 24 publications

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“…Using the spatial carrier frequency method [11,12] one can numerically reconstruct the phase distributions and which correspond to the two measurements. Errors with lateral extensions from 2 µm and minimal depth of at least 5 µm can be detected [3]. An example of the resulting real amplitude reconstructed from the hologram captured for λ = 638.13 nm is shown in Fig.…”

Section: Surface Measurements Of Micro Componentsmentioning

confidence: 97%

“…It is noted that there exists an angle  between the observation and illumination direction. Numerically the phase distribution corresponding to each measurement, is reconstructed utilizing the spatial phase shifting method, where the carrier frequency is controlled by shifting the position of the reference wave with respect to the optical axis [3]. Thus, the setup was used to register the phase information in the plane, which is close to the surface of the object under test.…”

Section: Digital Holographic Microscopymentioning

confidence: 99%

“…The camera sensor is an AVT prosilica GT 2750 having 27502200 pixels, where the pixel pitch is 4.54 µm. It should be noted that the test object is illuminated from four different directions and four holograms are recorded on single-shot using four reference waves by applying the digital holography multiplexing principle [3]. These holograms are used to reduce speckle noise in two wavelength contouring.…”

Section: Surface Measurements Of Micro Componentsmentioning

confidence: 99%

“…micro cold forming, however, allow for production rates of multiple parts per second. Presently, there exist no solutions that are fast, precise and suitable for in-process measurements at the same time [3].…”

Section: Introductionmentioning

confidence: 99%

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Fast Quality Inspection of Micro Cold Formed Parts using Telecentric Digital Holographic Microscopy

et al. 2018

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Quality inspection is an integral part of the production process and often part of the quality management agreements between manufacturer and customer. Especially when it comes to safety-relevant parts, i.e. in the automobile or medical industry, often a 100% quality inspection is mandatory. Here, we present a solution comprised of a digital holographic measurement system, as well as fast algorithms for geometric evaluation and surface defect detection that paves the way for the inspection of metallic micro cups in less than a second. By use of a telecentric lens instead of standard microscope objective, we compensate scaling effects and wave field curvature, which distort reconstruction in digital holographic microscopy. Due to limited depth of focus of the microscope objective, depth information from different object layers are then stitched together to yield 3D data of its geometry. The resulting point cloud data is automatically decomposed into simple geometric shapes in order to analyse geometric deviations. Amplitude as well as phase distribution images are then analysed for surface defects. Our approach is demonstrated by inspecting cold formed micro cups. Defects larger than 2 μm lateral resolution and 5 μm depth can be detected.

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Section: Surface Measurements Of Micro Componentsmentioning

confidence: 97%

Section: Digital Holographic Microscopymentioning

confidence: 99%

Section: Surface Measurements Of Micro Componentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Fast Quality Inspection of Micro Cold Formed Parts using Telecentric Digital Holographic Microscopy

et al. 2018

Self Cite

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“…Achieving 100% quality inspection is especially challenging in the micro-domain, e.g. when measurement uncertainty has to be in the range of a few microns, as there is usually a trade-off between precision and speed [Ago17]. Processes like micro cold forming, however, allow for production rates of multiple parts per second [Flo14].…”

Section: Introductionmentioning

confidence: 99%

Quality Control and Characterization

Maaß

Piotrowska-Kurczewski

Agour

et al. 2019

Lecture Notes in Production Engineering

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Quality inspection is an essential tool for quality assurance during production. In the microscopic domain, where the manufactured objects have a size of less than 1 mm in at least two dimensions, very often mass production takes place with high demands regarding the failure rate, as micro components generally form the basis for larger assemblies. Especially when it comes to safety-relevant parts, e.g. in the automobile or medical industry, a 100% quality inspection is mandatory. Here, we present a robust and precise metrology method comprised of a holographic contouring system with fast algorithms for geometric evaluation and surface defect detection that paves the way for inspecting cold formed micro parts in less than a second. Using a telecentric lens instead of a standard microscope objective, we compensate scaling effects and wave field curvature, which distort the reconstruction in digital holographic microscopy. To enhance the limited depth of focus of the microscope objective, depth information from different object layers is stitched together to yield 3D data of its complete geometry. The 3D data map is converted into a point cloud and processed by geometry and surface inspection. Thereby, the resulting point cloud data are automatically decomposed into geometric primitives in order to analyze geometric deviations. Additionally, the surface itself is checked for scratches and other defects by the use of convolutional neural networks. The developed machine learning algorithm makes it possible not only to distinguish between good and failed parts but also to show the defect area pixel-wise. The methods are demonstrated by quality inspection of cold formed micro cups. Defects larger than 2 lm laterally and 5 lm axially can be detected.

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Strategies for reducing speckle noise in digital holography

Bianco¹,

Memmolo²,

Leo³

et al. 2018

Light Sci Appl

225

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Digital holography (DH) has emerged as one of the most effective coherent imaging technologies. The technological developments of digital sensors and optical elements have made DH the primary approach in several research fields, from quantitative phase imaging to optical metrology and 3D display technologies, to name a few. Like many other digital imaging techniques, DH must cope with the issue of speckle artifacts, due to the coherent nature of the required light sources. Despite the complexity of the recently proposed de-speckling methods, many have not yet attained the required level of effectiveness. That is, a universal denoising strategy for completely suppressing holographic noise has not yet been established. Thus the removal of speckle noise from holographic images represents a bottleneck for the entire optics and photonics scientific community. This review article provides a broad discussion about the noise issue in DH, with the aim of covering the best-performing noise reduction approaches that have been proposed so far. Quantitative comparisons among these approaches will be presented.

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Spatial multiplexing digital holography for speckle noise reduction in single-shot holographic two-wavelength contouring

Cited by 5 publications

References 24 publications

Fast Quality Inspection of Micro Cold Formed Parts using Telecentric Digital Holographic Microscopy

Fast Quality Inspection of Micro Cold Formed Parts using Telecentric Digital Holographic Microscopy

Quality Control and Characterization

Strategies for reducing speckle noise in digital holography

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