Digitalization and digital transition are frequently used terms in modern communication. We are far from underrating these global phenomenons that are strongly connected with the worldwide networking between all domains of the public, private, commercial, and industrial life. Facts as the transition of the classical Data-Internet to the Internet of Things IoT, and Industrial Internet, respectively, are more and more influencing all technologies and thus it is quite appropriate to think about the future of metrology in such a changing environment. But it should be noticed that at least since the widespread introduction of computer technology in the 80ths and 90th, optical imaging and metrology have already implemented the transition to digital technologies. Methods such as digital image processing, digital holography, digital microscopy, and digital image correlation are state of the art by now. Manifold worldwide installations like digital/virtual/remote labs and robotic telescopes/microscopes support the position, that not only the simple transition from analog to digital but even more the total networking between complex physical entities and a new quality of data acquisition, processing and evaluation are characteristic for the new quality of imaging and metrology. In this paper we discuss the state of the art, the challenges, and the perspectives of optical metrology in times of digital transition.

In the measurement of three-dimensional structure beyond the diffraction limit of the objective using the speckle interferometry, it has been reported that the shape of a measurement object can be measured by detecting the change of phase distribution generated by a lateral shift of the object. In this method, it is a feature that the focused image of the measured object is not required by using a scattering light. In this paper, the principle of this method is investigated by using electromagnetic analysis. Even if the three-dimensional structure is beyond the diffraction limit of the objective lens, it is confirmed that the three-dimensional shape can be measured by using the scattering light as the illumination light.

The Centre Spatial of Liege (CSL) is involved from more than 10 years in the BTDF/BRRDF metrology of large Lambertian diffusers used for on-board calibration on space instrumentation. In this context, a dedicated automatized BSDF calibration facility has been developed, suitable for calibration of all types of diffusers (from industry to space applications). Accurate calibration of such systems induces constraining requirements on the calibration bench: manipulate large diffusers and mechanisms in class ISO5 environment; incidence beam divergence close to the Sun divergence; large spectral range coverage; measurement of very low diffused signals (highly stable, with low noise, straylight free set-up), high accurate measurement of attenuator and a high knowledge of all calibration properties for BSDF modelling. Based on previous heritage, recent improvements have been implemented in order to correct some defaults like mechanical stabilities (complete new design), specimen alignment (new iterative procedure), absolute error (super stable light bulb, improved filters wheel repeatability, optics to limit diffraction effects in UV, incidence beam non-uniformity compensation …). This paper presents the design of the improved bench, highlights critical parameters for BTDF/BRDF calibration and relates main improvements to reach todays performances. The current bench performances are illustrated by calibration campaigns results performed at CSL for Sentinel 2, Sentinel 3 and Sentinel 4 calibration assemblies.

Surfaces featuring complex topographies, such as high slope angles, large curvatures and high aspect-ratio structures on both macro- and micro-scales, present significant challenges to optical measuring instruments. Here we demonstrate a method to characterise and correct the three-dimensional surface transfer function (3D STF) of a coherence scanning interferometer (CSI). Slope-dependent errors present in the original measurements are reduced after phase inversion of the 3D STF, and the final results agree with traceable contact stylus measurements within the 30 nm reproducibility of the stylus measurements. This method enables in-situ compensation for errors related to aberrations, defocus and diffraction.

Corneal topographers based in Placido disks are widely used for their simplicity and easy implementation, however, this technique has an inherent error known as the skew ray error, which is generated by the problem that exists during the integration to relate a single point on the Placido screen with its correspondent point in the captured image. In this research work, we present a proposal of integration to recover the corneal topography from Placido disks images, which could eliminate the skew ray error. This process is made in a post-processing step, right after a meridional integration. The proposed integration is based under the hypothesis that the meridional integration really has information about the topography changes in the angle direction. The effect of the proposed technique over a topography is presented.

Dark field illumination (DFI) is an elegant inspection technique sometimes used to detect particles on a specular surface. However, traditional DFI struggles with repeatability, limiting its applications in automated inspection. We present an improvement to DFI by introducing a modulated dark field illumination (MDFI) that utilizes the phase rather than the intensity in the detection of defects. For modulated dark field illumination (MDFI), the phase-based information is independent from the reflectance of the surface, but has a higher sensitivity to the light scattered from a defect than DFI. As a result, we obtain a robust computational image process method that is insensitive to the environment and provides clearly defined defect information. In order to extend the application to industry, the instantaneous MDFI systems were developed and validated.

The number of patterns used to reconstruct one 3D image is of great importance to high-speed 3D shape measurement. This paper presents a method to reduce the number of patterns by using Hilbert transform with only three binary patterns. Two fringe patterns at different frequencies and one DC component pattern are used for absolute phase retrieval. We directly applied Hilbert transform to the difference maps generated by subtracting the DC component from the fringe patterns. Then, with two-frequency phase unwrapping method using geometric constraints, the absolute phase is retrieved robustly. We designed a system to capture 2D images at 6,000 Hz, and achieved 3D geometries at 2,000 Hz. Experimental results verified the success of the proposed method.

A novel aspherical surface measurement system based on randomly encoded hybrid grating (REHG) wavefront sensor is proposed. The system utilizes a non-null testing compensation lens to partially compensate the normal aberration of aspheric surface under test, which is more general than the null testing system. Different from the conventional interferometers, the REHG wavefront sensor exhibits strong anti-vibration ability and larger dynamic range due to its common path and self-reference characteristics, and is especially suitable for the measurement of aspherical surface. In this paper, a simulation model combing quadriwave lateral shearing interferometry based on the REHG and non-null aspheric testing technology is established. The generation mechanism of retrace error is analyzed. The iterative reverse optimization (IRO) retrace error correction method based on system modeling is discussed. Computer modeling is performed based on the actual experiment configuration, and an optimization function is set with polynomial coefficients of aspherics under test as variables. Through the reverse optimization with iterative ray tracing, the retrieved wavefront of the REHG sensor in the actual experiment system and the simulated wavefront in the system model will meet the constraint condition, and the figure error of aspheric surface can be then reconstructed by the optimal solution of polynomial coefficients in the model. The feasibility and accuracy of the aspherical surface non-null measurement system based on the REHG wavefront sensor are demonstrated by the simulation experiment result with different asphericities.

This work presents a novel microscopic profilometry using diffraction image correlation, which is appropriate for in-situ automated optical inspection (AOI). In contrast to the traditional confocal microscopy, the developed technique replaces the detector pinhole by observing and matching the diffraction patterns. Thus accurate surface depth detection can be achieved by eliminating time-consuming vertical scanning operation. The development is the first attempt in optics to use image correlation between the pre-calibrated database of diffraction images and the measured one of the detecting object surface. The feasibility of the method has been theoretically verified by scalar diffraction theory, then verified by experimental testing. Also, a depth response curve with the physical meaning of similarity is introduced and interpreted. Meanwhile, multi-point lateral scanning in one field of view (FOV) is achieved by quickly switching micromirrors on the digital micromirror device (DMD), thus the quasi full-field 3-D reconstruction can be acquired by combining tens of captured images. Verified experimentally, a 3-D reconstruction with sub-micrometer vertical resolution can be realized, with a tunable lateral resolution.

A numerical method for decomposing discrete wavefront aberration data into their individual azimuthal orders is presented. The approach utilizes the multi-angle averaging method, where the wavefront error is averaged under m equally spaced angular positions. This angular averaging cancels out all those contributions that are not integer multiples of the number of angular positions. Generally, the sampling theorem gives the maximum angular order that can be resolved by the given discrete data set. By combining the multi-angle averaging method at different m with the sampling theorem one can extract not only any distinct azimuthal order including their harmonics but in particular also each fundamental angular order. The basic algorithm is explained and numerically demonstrated. It is also shown how this approach compares to other angular decomposition methods such as Fourier filtering and Zernike decomposition.

The Shack-Hartmann Wavefront Sensor (WFS) is well-known in the fields of optical metrology, wavefront sensing in astronomy, and ophthalmologic control applications. The purpose of this communication is to bring new insights on the historical Hartmann test and to compare it with the less known reverse Hartmann test, where the locations of the pupil mask and observed image planes are exchanged. Both tests can actually be interpreted by using the formalism of Fourier optics, i.e. Fraunhofer diffraction for the Shack-Hartmann and Fresnel diffraction in the reverse configuration. The principles of these models are firstly described in the communication. The results of numerical simulations are then presented, allowing comparing both optical arrangements from the Fourier optics point of view, in terms of achievable wavefront measurement accuracy. They show that a WFS based on the reverse Hartmann test may globally achieve the same performance as the classical Shack-Hartmann.

Directed energy systems developed to reside on airborne platforms can experience a multitude of sources of degradation that reduces system performance. Three major sources of these degradations, or aberrations, can be attributed to aero-optics, atmospheric turbulence, and thermal blooming. Aero-optics is the term used to describe the aberrations induced from the aero-dynamical environment surrounding an aircraft as it travels through the air at high speeds. The Air Force Research Laboratory (AFRL) Laser Division has built and recently brought online the Aero-Effects Laboratory (AEL) capable of performing various aero-optical experiments and testing. The AFRL AEL currently has a supersonic wind tunnel with a test section that allows large optical access for various article testing and system simulations and verifications. Here we present the current status and capabilities of the AEL and some initial results from various experiments currently in development. Data acquisition systems include the use of pressure sensors, pitot probes, Schlieren imaging, and wavefront sensors. The Schlieren imagery is used to provide a qualitative measurement of the flow and shock waves present in the wind tunnel while wavefront sensors provide a more quantitative measurement of the phase disturbances induced from the aero-optical aberrations.

The Air Force Research Laboratory (AFRL) Directed Energy Directorate has built a supersonic wind tunnel in order to characterize aero-optical effects. Aero-optics is the study of the effect of aircraft-induced and atmospheric disturbances on the efficiency of optical imaging and laser systems. The Aero-Effects Laboratory (AEL) at AFRL consists of a supersonic wind tunnel with the capability of imaging the turbulent flow with large optical access of its test section. In order to gain access to the area of interest, we must first send a beam of light through the access windows of the wind tunnels test section to measure and visualize the flow. Initial measurements have been made and shockwaves between the mating plates of the test section and nozzle have been observed. This paper describes the optical system designed for resolving these shockwaves with a Schlieren imaging system.

High speed time-resolved wavefront and imaging measurements were taken synchronously in-flight through the boundary layer and the shear layer environments around the Airborne Aero-Optical Laboratory for Beam Control (AAOL-BC). Instantaneous point spread functions were generated using wavefront data which enabled a relationship between largescale structures present in turbulent flows and resultant instantaneous image degradation to be identified. In this manner, image blurring patterns can be related to specific flow structures which begins to abridge the knowledge gap between treating quantitative wavefront properties and the resultant blurred images.

Interferometers for the measurement of surface form and texture have a reputation for high performance. However, the results for many types of surface features can deviate from the expectation of one cycle of phase shift per half wavelength of surface height. Here we review the fundamentals of imaging interferometry and describe ways of defining instrument response, including the linear instrument transfer function. These considerations define practical regimes of linear behavior that are usually satisfied for traditional uses of interferometers; but that are increasingly challenged by applications involving complex textures and high surface slopes. We conclude by proposing pathways for further improving performance on difficult surface structures using advanced modeling techniques.

Depending on its stage skin cancer can be diagnosed through the so called ABCDE rule, which is mainly qualitative and noninvasive; besides this, there exists a technique that uses a dermatoscope to analyze the damaged area considered as noninvasive. On the other hand, the invasive methods mainly use sample-biopsies extracted from the affected area which are usually analyzed with a microscope or other imaging techniques. Digital holographic interferometry (DHI) has shown to be a powerful technique to obtain 3D information of a sample, and in these times, as many other optical metrology techniques, it has been widely applied to study biologic samples. In this research work, we present some initial 3D morphology measurements of melanoma cells made with a DHI setup implemented in a microscope type arrangement so a magnified image of the sample is studied. The morphology data depict the actual 3D contour map of the cell nucleus and represents a further advancement in the application of DHI to accurately study and measure the structure of cells.

Recovering the phase of radiation is of general interest in material and biomedical science, and in nanotechnology. Commercial interferometers have been widely used in a variety of applications, if equipped with a spatial light modulator or a computer generate hologram, theoretically the interferometer can measure a variety of surface objects. At present, the new non-interferometric quantitative phase recovery method based on Transport of Intensity Equations (TIE) is widely used in the field of microstructure measurement and bioimaging. Compared with interferometric measurement, the Transport of Intensity Equations does not need additional reference light, and has good ability of anti-vibration. In this paper, the ubiquitous interferometer and the new d’Nanoimager based on the Transport of Intensity Equations (TIE) are compared with respect to measuring larger objects of different profiles. These two methods are compared with respect of their accuracy and resolution of measurement and speed of acquiring data and other experimental consideration. In addition, a large number of subjects are selected for specific applications include flat surface such as the display screen of smartphones, to lens testing both spherical and cylindrical lenses and specific application such as corrosion pitting of aluminum disks. The comparative advantages and dis-advantages of the two methods are explored, as well as their application.

An important characterization for surface topography instruments is a traceable calibration of the height scale. We calibrate our coherence scanning interference microscopes using a natural spectral emission line in place of a sequence of material measures such as step-height specimens. The uncertainty budget for our approach includes estimates for several error sources associated with long term drift. Here we summarize results collected over 3 years’ experience from our laboratories to provide statistical support for confirming and refining these uncertainty contributions. We find that the source wavelength stability is < 0.005% RMS and the stability of the height scaling factor (the amplification coefficient) is < 0.02% RMS over 900 days. Both values are better than our original estimates. We also show < 0.13% RMS reproducibility of the complete traceable process using acceptance test data for over 100 manufactured instruments. Finally, we report results of 3 years of experience in certifying step-height specimens using the traceable wavelength method.

High radiation levels, ultra-high vacuum, cryogenic temperatures of the measured components and high electro-magnetic noise push accelerator surveyors to look for more robust and accurate solutions of alignment. In the framework of the High-Luminosity LHC project at CERN, a range of new and cost-optimized solutions using Fourier analysis based Frequency Sweeping Interferometry (FSI), are under development. The technique allows the measurement of absolute distances to multiple targets simultaneously and is less sensitive to reflected optical signal intensity variations. The advantage with respect to classical interferometers (based on the detection of interference signal phase-change and sensitive to light quality) is that even weak interference beat frequency peaks can be easily retrieved from the Fourier spectrum without significant degradation of measurement precision. Moreover, the detectability of light reflected from different types of surfaces (high and low reflectance ones) makes it possible to develop a new family of simple, universal and robust micrometric sensors for harsh environments, like particle accelerators. An application of this novel method is the monitoring of the position of magnet and crab cavity cold masses inside their cryostats. For this purpose, specially designed divergent beam FSI vacuum optics and low cost glass ball reflectors are being tested and will be used in the HLLHC project. A new family of simple and cost-optimized, single and multi-reflection sensors (levelling, inclinometer, distance) is under development in the same coordinated effort. This paper describes such a measurement system, the sensor design approach, the results obtained and their final use in the LHC accelerator.

We model a set of Phase-Shifting Interferogram (PSI) images in a new and versatile way that allows exploring interesting numerical approaches for the analysis of PSI. We show how this representation can be used to recover the modulating phase if the phase steps are known, and we also show how it can be used as the baseline for an iterative algorithm. For the case in which the phase steps are known we compare against the four step algorithm. For the case of unknown phase steps, we compare against the Principal Component Analysis (PCA) and the Advanced Iterative Algorithm (AIA).

A new kind of interferometry is presented, based on the maximal disorder of a single-frequency laser light coherently resonating inside a closed cavity with diffuse reflective walls. After thousands of Lambertian reflections, the optical field at any point inside the cavity is the coherent superposition of a huge number of modes that individually and independently obey a single probability distribution, which is invariant by rotations and translations regardless of the cavity geometry. The resulting interference speckle field has the same statistical properties and exhibits extreme sensitivity to phase fluctuations. From speckle intensity fluctuations, we can measure the various causes that perturb light propagation, be it deformations of the cavity, dynamic scattering of the propagation medium, or fluctuations of the input light phase. Preliminary experiments indicate that strains down to 10^-10 can be detected, that correspond to picometer cavity deformations. This concept of ”scrambled” interferometer opens new possibilities in the field of accelerometry or vibrometry, as well as for the enhancement of dynamic or multiple light scattering techniques.

Phase-measuring deflectometry (PMD) is an established measurement method for determining the topography of specular free-form surfaces. However, since each camera pixel only contains information about the location of the observed screen point, but not about the incident ray direction, the surface slope cannot be determined unambiguously without prior knowledge of the height. In order to overcome this difficulty (known as the ”height problem” of PMD), several cameras with overlapping fields of view are often used. This, however, requires a very large screen and additional installation space in order to ensure sufficiently diverse viewing directions within the overlap region. Other solutions, such as multiple measurements with shifted screen positions or the use of additional measuring equipment to determine the object position, also have considerable drawbacks due to the longer measurement time and the greater calibration effort. A new method is presented which avoids these disadvantages.

Phase Measuring Deflectometry (PMD) is a non-coherent full-field measurement technique based on geometrical optics, usually employed for specular surfaces. The measured phase in PMD corresponds to the position on the display recorded by the camera pixels. Concerning the measurement uncertainty in PMD systems, the camera can be regarded as the best described and most thoroughly modelled part, followed by the display with its nonlinearity or flatness deviation of the monitor surface shape. However, the effect of the properties of technical surfaces on the measurement deviation still lacks detailed investigation. As the errors in phase measurement will introduce subsequent errors into the slope and shape measurement, it is important to study these error sources. This paper investigates the effects of the properties of technical surfaces on phase measurements in a PMD system. We demonstrate the dependence of the deviations of phase measurements on surface roughness using well-defined samples manufactured by high precision diamond turning.

Digital focusing schlieren relies on accurate mapping between a camera and a digital modulator or display system. Our early development of the technology was challenged by higher-order distortions in the optical systems. A simple perspective transform was adequate for lower-power lenses and smaller fields of view, but for wide fields and for highly sensitive configurations such as dark-field schlieren, correction terms were necessary. The Brown-Conrady model fitting implemented by OpenCV offered little improvement, so we developed a new distortion correction method that empirically optimizes the schlieren filter performance and constructs a map with phase unwrapping techniques borrowed from interferometry. This approach allows operation even with wider-angle lenses and finally makes dark-field schlieren practical. It also appears to improve the resilience of the grid generation with lower resolution camera systems, which is important for implementation in high speed schlieren imaging.

Phase measuring deflectometry is a powerful in-situ measuring technique for complex specular surfaces. Its measuring accuracy depends on the quality of geometric calibration. An in-situ deflectometric measuring system is integrated into a single point diamond turning machine. An accurate self-calibration method is proposed to refine the positions of the camera and the screen. A world coordinate system is established by introducing a flat mirror without markers. The geometric positions are solved by minimizing the deviations of the traced screen pixels. The tracing deviations caused by the form errors behave differently with those caused by the position errors. Precise localization of the measured surface can be realized by error separation, so that detecting of feature points can be avoided. Experimental results demonstrate that the measurement error is below 300 nm.

Point spread function (PSF) of projector plays an important role in coaxial projection-imaging profilometry and binary defocusing fringe projection profilometry. In the proposed method, the SPI (Single Pixel Imaging)-based PSF measurement method has been used to obtain the PSF of the projector point by point. We use the camera to capture the SPI patterns projected by the projector on a white plane. By considering each pixel of the camera as a single-pixel detector, we can apply SPI technology to the camera pixels and acquire the light transport coefficients between the object points on the white plane and image points of projector, which is the spatially varying blur. Owing to the characteristic of SPI, the proposed method could obtain the spatially varying blur of every pixel directly. The experiment also verified that the proposed method could provide a more accurate blur kernel than the traditional Gaussian blur kernel to fit the blur model of the camera lens.

International standard on diffraction efficiency of hologram has been published on 2015. Although the diffraction efficiency is one of important factor to evaluate hologram, there are no other international standard for display hologram. This presentation introduces some activities toward standards. One is objective image quality evaluation of reconstructed images from hologram. The work evaluates signal-to-noise ratio or structural similarity index and diffraction efficiency. The results show that the amplitude hologram has better image fidelity though diffraction efficiency is much lower than the phase hologram. The other work is one of subgroups of JPEG (well known as still image compression standard) is now considering standards to compress and evaluate digital hologram data.

Methods for specifying and evaluating light-based media and devices have become commonplace in various industries such as the professional luminaire industry. This is not the case with Holography as there are no standards that address specifying, evaluating, and displaying holograms. If methods are considered, then standards can be addressed. Three measurable characteristics of holograms are considered. This paper reviews Kelvin temperature for correct color rendition, goniometry for hologram angle of view, and signal-to-noise ratios for efficiency. This paper is relevant to the independent holographer or anyone contracting a hologram facility to custom produce holograms that are reconstructed with a white point source of light. The focus of this paper is analog image / light pattern holograms for display.

Facing the absence of quality standards in the computer generated holography industry; we often see a wide range of quality levels in holograms. Accessibility to CG holography laboratories is still limited. This situation doesn’t help the artists who need to experiment and adapt their working process to the requirements and the particular features present in the current state of synthetic holography. Previous work afforded me the opportunity to perform Image Quality Analysis in the development of a computer-generated holographic imager, and to produce experimental large size artistic holograms. I will present in this paper some key elements and needs related to the optical and spatial characteristics of synthetic holograms that can insure high quality in holographic art. Topics such as level of detail, resolution, brightness and contrast, depth and field of view, distortions and defects, will be discussed as well as some content effects specific to synthetic holography such as kinetics and spatial synchronization. Holography, and especially synthetic holography, is a young field of research, in art as well as in science. Holography experiments in collaborative science and art are still strongly needed.

Structured light systems (SLS) have become increasingly important for three-dimensional shape measurements. A quantitative evaluation of the spatial resolution is also becoming increasingly important. The spatial frequency response of the instrument is a reasonable metric for resolution and is commonly referred to as the instrument transfer function (ITF). In this paper, we present a methodology to estimate the ITF of a commercial SLS (the EinScan-Pro 3D Scanner) and its uncertainty. A measurement of a step artifact is used for the ITF estimation. We also discuss a method to check the validity of the artifact used for the measurement. The ITF dependence on step orientation and position in the measurement volume is also presented, in addition to a comparison between ITF and the modulation transfer function (MTF) for the cameras in the instrument.

Liquid crystal on silicon (LCoS) based spatial light modulator (SLM) is widely used in research areas such as holography display and optical measurement. However, a certain aberration term to the incident wavefront is introduced due to the curvature of the LCoS backplane, and the correction of this phase aberration is important to improve the accuracy of phase modulation by the SLM. In this paper, we propose to use several phase retrieval techniques to measure the corresponding wavefront directly and employ the obtained wavefront to correct the aberration introduced by the curvature. An interferogram acquisition technique based on the self wavefront modulation of SLM is proposed. Besides, a method for determining the corresponding active area of the LCoS backplane and parameters of 2-D projective transformation is proposed to transform the active area to the fitted resolution of the SLM. A RMS value to approximately λ/32 after correction is achieved.

Surface defects inspection is a critical part in manufacturing of mobile phone cover glass. Considering the defects in the optical elements surface caused by the imperfection of manufacturing technique, the classification and the position information should be carried out for the necessary repairing process. The traditional manual inspection method is always labor-consuming and inefficient. Surface defects digital evaluation system based on machine vision draws much attention in the recent years. This paper proposed algorithms and applications for the detection task with higher efficiency and reliability comparing to the manual inspection. The detection method is based on machine vision and machine learning techniques. The images of optical elements surface are captured by line-scanning cameras, with the imaging systems of dark-field, bright-field and transmission-field. Only one image system is not enough to detect all kind of defects like scratch, bubble, crack of glass and edge chipping etc. The position information and category of defects are obtained based on image processing technique. The defective area was calculated by image filtering algorithm, the feature selection techniques based on segmentation methods are explored and the feature vector can be extracted before the next step of classification with Support Vector Machine (SVM) technique. Verified by the experiments, the results reveal this method has good performance and is very suitable for recognition and classification of glass defects.

In the image-based industrial inspection field, the imaging distance between the scene and the camera is relatively short, and the field-of-view of the imaging system is too small to meet the requirements of detection. So a close-range image stitching method is needed to get high quality and large field-of-view images. The traditional image stitching method uses a global homography transformation matrix for image stitching, which is stable, but only suitable for flat scenes, remote scenes or the scenes which are captured by the camera with rotation only. The As-Projective-As-Possible and Content- Preserving-Warping methods, which are realized by mesh optimization, improve the stitching result to a certain degree, but there will still have obvious ghost for the close-range scenes and images which have relatively large parallax. In this paper, an image stitching method which utilizes depth information and mesh optimization is proposed. The feature points are detected and clustered, and the depth information and grouping points are used to assign weights to each mesh to compute homography for each mesh respectively. Other state-of-the-art methods are compared with our method, it can be seen that the proposed method can get a better result.

The sharp edges of most precision machined surface must be ‘broken’, which involves rounding them or adding a flat chamfer. Part longevity, human safety during handling, and proper performance of the component is the intended application of this edge breaking. Traditional visual inspection or single-trace metrology is insufficient to assure parts are within specifications. This paper will present a handheld, 3D-measurement device using polarized structured light which allows for rapid, simple, shop-floor measurement of edge break, chamfer angles, and other precision part geometries. A variety of component measurements will be presented along with studies on accuracy, repeatability, and reproducibility in real-world environments.

CCD-based thermoreflectance imaging is a powerful tool for high-resolution, 2D thermal imaging. Given the low signalto- noise ratio, thermoreflectance imaging is typically performed using a lock-in imaging, “4-bucket” algorithm that requires averaging over many (typically 10³-10⁴) sample modulation periods, leading to relatively long measurement times. However, averaging over multiple samples in the presence of noise also has the potential secondary effect of stochastic resonance enhancement, in which signals smaller than the bit depth of the camera can be measured, dramatically improving the thermal resolution. In this study, we develop a model of stochastic resonance enhancement of the image “buckets” through additive noise, quantization, and averaging. We demonstrate that for noise amplitudes greater than 1.25 least significant bits (LSB), the root mean square (RMS) error in an image bucket is independent of the input signal amplitude. In addition, we show that for input signals for which the image quantization error is greater than 0.5 LSB, the RMS error in an image bucket is minimized in the presence of small, non-zero, amounts of noise, demonstrating stochastic resonance enhancement. Our simulations confirm earlier results that an image bucket may be modeled as a Gaussian-distributed random variable, but the expected mean is offset due to the flooring quantization scheme. Finally, our results for experimentally reasonable noise and signal levels suggest that for measurements made using low numbers of iterations (<5000), a small tuning of the CCD camera noise could increase the stochastic resonance enhancement of the image bucket.

The availability of commercial light field cameras has spurred significant research into the use of light fields and multi-view imagery in computer vision. In this talk, we discuss our results over the past few years, focusing on a few themes. First, we describe our work on a unified formulation of shape from light field cameras, combining cues such as defocus, correspondence, and shading. Then, we go beyond photo-consistency, addressing non-Lambertian objects, occlusions, and material recognition. We also discuss applications for light field cameras such as motion deblurring and descattering. Finally, we show that advances in machine learning can be used to interpolate light fields from very sparse angular samples, in the limit a single 2D image, and create light field videos from sparse temporal samples.

Several volumetric reconstruction algorithms are surveyed and evaluated using plenoptic images of a burner flame. Automatic generation of static and dynamic masks is implemented to limit the scope of the reconstruction problem. Volumetric reconstructions of the flame are performed using all surveyed algorithms with a number of plenoptic cameras ranging from one to four. Simultaneous Algebraic Reconstruction Technique (SART), a reconstruction algorithm widely used in medical imaging, is identified as the most promising algorithm of those surveyed. When combined with inter-iteration minimization of L1 Total Variation (TV-L1), SART-TV reconstructions of a burner flame are shown to be smooth, circular, and uniform. Two-camera reconstructions recover the approximate shape of the flame, yielding qualitative information about the flame structure. Three-and four-camera yield the full three-dimensional flame structure.

This paper presents a methodology to obtain three-dimensionally (3D) resolved measurements of temperature, soot volume fraction, and excited state radical concentration in a volume of luminous combustion gases using light field imaging with a plenoptic camera. The technique involves measurement of emission intensities at multiple wavelength bands selected to enable two-color pyrometry of soot particles and chemiluminescence of CH* and C₂* radicals. The feasibility of this method was tested using laboratory flames and reconstruction algorithms that were developed previously for 3D imaging of discrete particles. The results show that the existing algorithms reproduce the basic structural features of the flame but with limited spatial resolution, demonstrating feasibility but also revealing the need for improved algorithms for volumetric reconstruction. Quantitative measurements of temperature and soot volume fraction were obtained that were in good agreement with independent measurements using conventional techniques and distributions of CH* and C₂* were obtained that were consistent with expected trends.

The paper describes and demonstrates a non-destructive evaluation method that can perform in space, in situ, and postproduction inspection for metallic and non-metallic products of additive manufacturing. The method, which is based upon measuring the vibrational spectrum of an object and using it as a unique acoustical signature is capable, not only of detecting defects and flaws, but also doing this in situ. The method combines Laser Doppler vibrometry with acoustical resonance spectroscopy to extract acoustical information from exposed layers during the printing process to characterize the part at any stage during its manufacture. Component samples with intentional defects were printed and correlated with vibrational signatures. In future work we plan to develop the necessary hardware and software to adapt and integrate the inspection system into commercial printing machines. The resulting machine will feature in situ monitoring of typical parts while being printed in the machine.

In this contribution we present a broadband static Fourier transform spectrometer (bsFTS) based on a single- mirror interferometer containing only off-the-shelf optical components and an uncooled microbolometer detector array. The system uses concave mirrors instead of lenses and therefore covers a wide spectral range from 3.6 μm to 17 μm at a spectral resolution of 12 cm^-1. Furthermore, dispersion effects can be minimized and the system can thus be designed with increased temperature stability. We demonstrate the optical and mechanical design of the current laboratory prototype and compare the instrument to a scanning Fourier transform infrared (FTIR) spectrometer. Additionally, we present a technique for simultaneously acquiring the sample spectrum and the background spectrum. Thereby, a variation of the background over time can be compensated continuously and hence the bsFTS presented in this contribution offers significant potential with regard to long-term stability.

To schedule fruit tree Syzygium samarangense to bloom and bear fruit is a challenging work, which requires highly experienced and knowledgeable professions. Specific amount of fertilizers should be supplemented at specific timing. Therefore, it is also a labor-intensive work. Our goal is to provide a method to automatically identify nutritional and growing conditions of Syzygium samarangense. In this work, we applied both multispectral and hyperspectral imaging techniques to measure parts of Syzygium samarangense, including branches, leaves, flowers, and fuiits. We examined several important spectral indexes: water content index, biomass content index, structure index, and chlorophyll content index. A custom-built hyperspectral imaging system was used here. The system includes two spectrographs, and two charge-coupled devices One of the spectrographs disperses light in visible wavelength, and the other spectrograph works in short wavelength infrared light region. With line-scanning data acquisition, the collected reflectance data included two-dimensional spatial image as well as reflectance spectrum. The hyperspectral imaging data were compared with results from a commercial multispectral imagery. The selected lightweight multispectral imagery was portable by an UAV. Among the spectral indexes we examined, data from the two techniques were highly linear correlated, indicating that data from multispectral imagery were sufficiently reliable for orchard management. On the other hand, additional spectral characteristics were only shown in hyperspectral imaging data. Calculated images that mapped hyperspectral indexes showed patterned of diseased area in leaves. Therefore, we built an on-site orchard monitoring procedure that combines both multispectral and hyperspectral imaging techniques for wax apple tree.

In this study, we propose a spectral-domain optical coherence tomography (OCT) method that employs pulse irradiation to capture an interferogram and continuous wavelet transform (CWT) for data analysis. The pulse irradiation technique enables obtaining an interferogram with a high signal-to-noise ratio, and the CWT allows accurate analysis of a nonstationary signal. Experimental results obtained using a cover glass of thickness 150 μm confirmed that the repetitive measurement error was 0.32 μm. However, this error was reduced to 0.23 μm when pulse irradiation was applied for image capture.

In this paper, we proved that the correspondence cue focusing on the local angular variance of the structured light field could provide constraint conditions to deal with the phase ambiguity. A novel method of light-field depth estimation directly using wrapped phases was proposed, avoiding system calibration and adapting to the measurement environment and requirements.

In this manuscript, a simple and low-cost method for phase-shifting interferometry by the rotation of a polarizer is presented. The principle of the proposal relies on the polarization aberration introduced by a cube beam-splitter due to its geometry, to the angular dependence with the coating and to the polarization angle of the input beam. The interferometric setup performs as a two-window common-path interferometer in which the added phase-shifting is achieved by simply rotating a polarizer at the interferometer output. The viability of the proposal is sustained with experimental results in which the phase-shift value and the resulting wavefront are calculated with Farrel’s technique and the Three-step PSI algorithm respectively.

In this study, we develop a 3D coordinate measurement system based on a multilateration technique and an absolute distance metrology for a mobile machine platform. Since the multilateration only uses distance values without angle measurements, it is possible to make 3D coordinate measurements with high accuracy in a large area. In addition, absolute distance is suitable for industrial application because of enabling real-time continuous measurement after the obstruction. The system is composed of four laser tracking stations and a four channel absolute distance meter which is a fs pulse laser based high accuracy absolute distance measurement. In order to measure 3D coordinate of targets, each tracker measures a distance value with real time tracking, and multilateration algorithm is applied to derive 3D coordinate values using the measured distance values. This paper introduces the multiple absolute distances based 3D coordinate measurement system and discusses in detail.

The inspection of particles plays an important role in quality control of smooth surfaces, such as optics and silicon wafers. The difficulty of inspection lies not only in the high-resolution detectivity for small-size particles, but also in the need to distinguish among different types of particles due to their different damages and re-work processes. This paper proposes a detection and discrimination method of the particles on (surface particles) and below smooth surfaces (subsurface particles) by laser scattering with polarization measurement. The incident laser beam passes through a polarization state generator (PSG) to illuminate the smooth surface. A large proportion of the particle-induced scattered light is detected after collected by an ellipsoidal mirror. Meanwhile, in the blind area of the ellipsoidal mirror, a small amount of scattered light enters the polarization measurement channel, where a polarization state analyzer (PSA) is used to finally obtain a two-dimensional polarization signal for discriminating the two types of particles. Then, by a nonlinear global search combined with the theoretical models for polarized light scattering from particles, the optimal polarization measurement state of the PSG and the PSA is obtained to maximize the separability between the surface particles and subsurface particles on the acquired polarization signals. This method takes full advantage of the polarization of scattered light, and with one single scan the inspection for the whole surface can be accomplished. Finally, experimental results demonstrate the effectiveness and accuracy of the method.

We have developed an absolute distance measurement system for the three-dimensional (3D) coordinate measurement. The final project goal is to develop a multilateration based coordinate measuring system for precise 3D positioning. This coordinate measuring system consists of an absolute distance measuring system and four laser tracking stations. Accurate positioning become possible by determining coordinates using only four distance values instead of angular measurements that cause major errors in the coordinate measurement. In each station, distance is measured by the absolute distance measurement system. There are several advantages to using absolute distance measurement instead of an incremental-type laser interferometer for 3D positioning. If the beam is accidentally broken, incremental-type devices must measure again from the beginning. However, in the absolute distance measurement, the distance of an object can be measured continuously without such a problem. The other is to improve coordinate measurement precision by reducing the number of variables in the multilateration algorithm. In order to measure high precision 3D position in a large area, we have developed a femtosecond laser based absolute distance measurement system. Two-femtosecond lasers and optical cross-correlation technique are applied to improve precision in the distance measurement. This method enables several micrometer-level distance measurement at distances of a few tens of meters.

The ever-increasing requirements of product quality and reliability demand more efficient measuring and test methods that must be online, nondestructive, wholefield and without contact. Optical methods seem to be ideal for such purposes. The interferometric technique of ESPSI (Electronic Speckle Pattern Shearing Interferometry), or Shearography, is a coherent-optical measuring and test method that is similar to holographic interferometry. However, this method displays many advantages for industrial applications, due to its relative insensitivity to environmental disturbances. Shearography measures the gradient of the deformation, not the deformation itself as holography does. Consequently, shearography measures strain information directly. Based on the above, Shearography was adapted for the surface strain measurement in graphene-reinforced composite materials; the information was evaluated at each point from our sample observed area. Defect inspections with shearography on fiber-reinforced plastics parts, widely used in aircrafts, ships, chemical and oil and gas industries, are often performed outside of the lab. An optical system capable of measuring the strain fields in and out of plane was developed based on electronic speckle interferometry. The obtained interferogram images were processed using the phase-stepping technique. A specific specimen geometry and an optical arrangement based on the Michelson interferometer are proposed to measure the deformation along two orthogonal axes due to sensibility in and out of plane. The advantages of the system include its high sensitivity and stability. The experimental setup and approach for estimating the strain fields was validated using a membrane based on polylactic acid reinforced with cellulose microcrystalline as sample with and without graphene.

High sensitivity magnetic field sensors have been applied to biotechnology problems such as magnetoencephalography and magnetocardiography. Unfortunately, the high cost and/or development of the sensors often limit the widespread use of these medical diagnostic systems. Fiber optic magnetostrictive sensors offer high sensitivities with competitive fabrication cost. Magnetostrictive sensors have experimentally demonstrated resolutions as low as 23 pT/√Hz without any mu-metal shielding. With respect to the sensor cost, fiber-optic-based magnetic field sensors leverage the advanced component development and the economies of scale of the telecommunications industry. In addition, the trend in interferometric sensor development has been to transfer the demodulation complexity from hardware to the digital signal processing algorithm. This reduction in hardware significantly reduces the cost of the overall sensor system. In this paper, we present a demodulation algorithm for an interferometric magnetic field sensor. The sensing mechanism is based on the magnetostriction of a material bonded to the optical fiber in the sensing leg of the interferometer. A phase-generated-carrier demodulation scheme is assumed. The algorithm features real-time demodulation of arbitrary signal waveforms. We present the theoretical derivation of the algorithm and verify its operation through computer simulation.

A new full-field profilometry based on diffraction image correlation (DIC) was developed in which the technique bases on calibrated database of reference diffractive images (RDIs) to estimate surface depth information. This technique has the advantage of removing vertical scanning for achieving high measurement efficiency in microscopic surface profilometry. However, as the diffractive images not only depend on the tested height but also the local surface tilt. Thus, the pre-built image database may not match the measured diffractive image and lead to a systematic measured error incurred by the surface tilting condition. Thus, in the article, the influence of surface tilt to the diffraction images is investigated and analyzed to understand the relationship between the surface tilt and the image variation. A lateral drifting phenomenon depends on the tilt angle and tilt direction was also quantified to estimate the impact of the tested surface height. Meanwhile, a detection algorithm to determine the center of diffractive image was developed to position the shifting quantity of the image. Moreover, the information coupling problem between height and tilting parameters, such as the tilt angle and tilt direction was studied to decouple these parameters from the tested height, so the tested surface can be reconstructed accurately. To realize the proposed method, some data processing strategies were also proposed to decouple the depth information from multi-surface parameters such as surface tilt angles (pitch and yaw) and direction effectively.

Patterned surfaces which include semiconductor devices, optical components and other functional surfaces play important role in recent manufacturing. Optical measurements with non-destructive property is available for them but further improvement in spatial resolution and throughput are necessary. In this study, structured illumination microscopy was employed for high-resolution wide-field measurement. Structured illumination microscopy has been usually applied for fluorescent bio-imaging. For non-fluorescent imaging and industrial applications, one problem is speckle noise in structured illumination generation and another problem is vibration and thermal drift in high-precision positioning of laser-interference standing-wave illumination. In our development, the phase of the structured illumination is detected as a fringe signal with another interferometric measurement system, which is employed by structured illumination microscopy as originally developed; it uses a low-coherence light source for high-resolution and low-speckle imaging. We constructed an optical system consisting of plural Michelson interferometers, which allow the low-coherence interference fringes to be manipulated on a sample and the phase to be detected on another sensor. Feeding back the phase of structured illumination through super-resolution processing allows robust imaging despite vibrations, drifting, and environmental changes. A series of experiments were performed to verify our developed microscope system applied for measurement of patterned surfaces.

A century has gone by since antennas were used for the first time to control emission and reception of many types of electromagnetic radiation. The reescalation of antennas to smaller sizes and the need of on a chip devices motivated the manufacture of the so called nano-antennas that can focus farther than the diffraction limit. It is well known that metallic particles sustain resonance plasmonic modes in visible wavelengths, making them natural optic antennas. As happened with the conventional radiative antennas, nowadays it is important to characterize the radiation pattern emitted by these nano-antennas. In this research, we pretend to characterize at least qualitatively the dynamic behavior of super paramagnetic nanoparticles by exposing them to an electromagnetic field generated by excited nano-antennas of the bowtie type. We use a confocal microscope since it is a technique that increases the contrast of an image by using a pinhole that obstructs the light that is out of the focal plane. This results in a system that not only discriminates field of view over the focal plane, but it also permits depth selection inside of the specimen under observation.