This PDF file contains the front matter associated with SPIE Proceedings Volume 10373, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Mid-spatial frequency (MSF) texture on optical elements degrade their performance. A Zernike polynomial representation of the wavefront can be used to characterize the mid-spatial frequency and predict the optical performance. The ability to generate very large orders of Zernike polynomials enables fitting and describing optical wavefronts all the way from low order form errors to mid-spatial frequencies. Based on a filtering aspect of Zernike polynomials, we show how different fabrication signatures affect optical performance differently. We investigate the Strehl ratio and Modulation Transfer Function (MTF) as optical performance metrics for mid-spatial frequency. We then present how the orthogonality properties of Zernike polynomials along with linear systems theory of MTF can provide an effective tool in separating the optical performance degradation due to different mid-spatial frequency texture. We present an example of real mid-spatial frequency texture to examine the error in the approximation of MTF when using linear systems formulation.

Photogrammetry based systems are able to produce 3D reconstructions of an object given a set of images taken from different orientations. In this paper, we implement a light-field camera within a photogrammetry system in order to capture additional depth information, as well as the photogrammetric point cloud. Compared to a traditional camera that only captures the intensity of the incident light, a light-field camera also provides angular information for each pixel. In principle, this additional information allows 2D images to be reconstructed at a given focal plane, and hence a depth map can be computed. Through the fusion of light-field and photogrammetric data, we show that it is possible to improve the measurement uncertainty of a millimetre scale 3D object, compared to that from the individual systems. By imaging a series of test artefacts from various positions, individual point clouds were produced from depth-map information and triangulation of corresponding features between images. Using both measurements, data fusion methods were implemented in order to provide a single point cloud with reduced measurement uncertainty.

A novel in-plane and out-of-plane deformation simultaneous measurement method using only two speckle patterns grabbed before and after deformation of an object with rough surfaces has been proposed. Then, the same measurement sensitivities in three directions can be set in this system. However, the method has some area which cannot measure a deformation. In this paper, new optical system which is not based on orthogonal laser beams is proposed to expand the measurement area of the method under consideration of measurement sensitivity. The improvement of deformation measurement area where the deformation distribution cannot be measured by the conventional optical system is discussed in the proposed method.

This paper proposes a new strategy of extracting boundary points from scanning point cloud (SPC) data of sheet metal parts (SMPs). This strategy is suitable for bending SMPs with slowly changing surfaces. To cope with the problem that the SMP is too thin to have enough points of its lateral surface to be calculated for the boundary outline, the boundary points are obtained by moving ridge points which is the maximum curvature points on the marginal of parts along theoretical position direction. In this article, the strategy is explained firstly and then carried out on two different experimental SMPs. The strategy contains several steps. Firstly, we construct a slice set called multiple direction slices (MDS) along a curve fitted by boundary points of SPC. Then marginal point data (MPD) is obtained completely and accurately by MDS. And then the chamfer arc data is extracted from MPD by setting identification model of chamfer arc’s two endpoints. Then the ridge points which are the maximal curvature points of chamfer arc data are picked out from chamfer arc data. Finally, by moving the ridge points along a certain direction for a fixed distance, the boundary points are calculated out. Two experiments are carried out to identify position error and form error of the extracted boundary points. The measurement results of boundary outlines of a 6mm thick SMP from a three coordinate measuring machine (CMM) is taken as reference in the first experiment. The second experiment regards theoretical boundary outline as reference. Both two experiments demonstrate the effectiveness of the strategy.

Industrial optical inspection often requires high speed and high throughput of materials. Engineers use a variety of techniques to handle these inspection needs. Some examples include line scan cameras, high speed multi-spectral and laser-based systems. High-volume manufacturing presents different challenges for inspection engineers. For example, manufacturers produce some components in quantities of millions per month, per week or even per day. Quality control of so many parts requires creativity to achieve the measurement needs. At times, traditional vision systems lack the contrast to provide the data required. In this paper, we show how dynamic polarization imaging captures high contrast images. These images are useful for engineers to perform inspection tasks in some cases where optical contrast is low. We will cover basic theory of polarization. We show how to exploit polarization as a contrast enhancement technique. We also show results of modeling for a polarization inspection application. Specifically, we explore polarization techniques for inspection of adhesives on glass.

In this paper, we report results of a high precision polarization state measurement of light based on the in-plane spin splitting (IPSS) in optical reflection. The IPSSs in the coordinate (spatial) and momentum (angular) spaces are respectively highly sensitive to the polarization rotation and ellipticity of the incident light at the Brewster angle. By measuring both the spatial and angular IPSSs with different post-selections, the full information of the polarization state (polarization angle and ellipticity) of the incident light can be obtained. Our research may be applied for the precision measurement of polarization-dependent effects.

In this paper, we present an alternative refractive index sensing scheme based on the photonic spin Hall effect (PSHE). We find that the spin splitting induced by the PSHE shows high sensitivity to the refractive index change (RIC) around the Brewster angle.The refractive index of sample is estimated with a precision of the order of 10⁻⁵ refractive index unit (RIU) by measuring the spin splitting with weak measurements. Compared with the surface plasmon resonance sensor, this method does not require the noble metal film and keeps the same sensitivity, which is a low-cost alternative to refractive index sensing.

Inspectors attempting to quantify defects and fine-scale features on precision machined surfaces are often limited by the capabilities and form factors of existing measurement techniques. Inspectors most often rely on imprecise and inaccurate visual comparison tools or pin gauges to determine the geometry of surface features. This paper will describe key attributes of a metrology system for quantification of small features in a production environment and present critical performance tests on the system including vertical and lateral resolution and correlation with other techniques. Additionally, various new applications will be discussed which are fundamentally enabled through access to a portable, vibration-immune, system that is both quantitative and easy-to-use.

Natural convection studies in an enclosure are very relevant since it spans a wide area of applications such as heat exchangers, chemical reactors, cooling of electronic equipment, etc. In the present study, an experimental investigation is performed in a rectangular cavity of dimension 46 mm x 23 mm with protruded copper half cylinders of diameter 15.8 mm (5/8 inch) each. Interferometry has always been a good technique for accurate measurements of temperature gradients. Mach-Zehnder interferometer is employed for visualising the isotherms and for quantitatively inferring the temperature gradient. The protruded half cylinders are maintained at constant temperature, ranging from 60°C to 120°C using an electric cartridge heater and associated temperature controller setup. A He-Ne laser with 24mm collimated beam size is used for experimental purposes. Temperature gradient variation along the radial direction is plotted against the circumferential angle of the cylinder and isotherm merging angle is determined for varying time step and varying cylinder surface temperature.

This paper describes an ongoing instrument development project to distinguish genuine manufactured components from counterfeit components; we call the instrument ASSURES (Authentication Sensing System Using Resonance Evaluation Spectroscopy). The system combines Laser Doppler Vibrometry with acoustical resonance spectroscopy, augmented with finite element analysis. Vibrational properties of components, such as resonant modes, damping, and spectral frequency response to various forcing functions depend strongly upon the mechanical properties of the material, including its size, shape, internal hardness, tensile strength, alloy/composite compositions, flaws, defects, and other internal material properties. Although acoustic resonant spectroscopy has seen limited application, the information rich signals in the vibrational spectra of objects provide a pathway to many new applications. Components with the same shape but made of different materials, different fatigue histories, damage, tampering, or heat treatment, will respond differently to high frequency stimulation. Laser Doppler Vibrometry offers high sensitivity and frequency bandwidth to measure the component’s frequency spectrum, and overcomes many issues that limit conventional acoustical resonance spectroscopy, since the sensor laser beam can be aimed anywhere along the part as well as to multiple locations on a part in a non-contact way. ASSURES is especially promising for use in additive manufacturing technology by providing signatures as digital codes that are unique to specific objects and even to specific locations on objects. We believe that such signatures can be employed to address many important issues in the manufacturing industry. These include insuring the part meets the often very rigid specifications of the customer and being able to detect non-visible internal manufacturing defects or non-visible damage that has occurred after manufacturing.

It is well-known that the surface roughness of materials plays an important role in the operation and performance of technological systems. The roughness influences key parameters, such as friction and wear, and is directly connected to the functionality and durability of the respective system. Tactile methods are widely used for the measurement of surface roughness, but a destructive measurement procedure and the lack of feasibility of online monitoring are crucial drawbacks. In the last decades, several non-contact, usually optical systems for surface roughness measurements have been developed, e.g., white light interferometry, light scatter analysis, or speckle correlation. These techniques are in turn often unable to assign the roughness to a certain surface area or involve inappropriate adjustment procedures. One promising and straightforward optical measurement method is the surface roughness measurement by analyzing the fringe visibility of an interferometric fringe pattern. In our work, we employed a spatial light modulator in the interferometric setup to vary the fringe visibility and provide a stable and reliable measurement system. In previous research, either the averaged fringe visibility or the fringe visibility along a defined observation profile were analyzed. In this article, the analysis of the fringe visibility is extended to generate a complete roughness map of the measurement target. Thus, surface defects or areas of different roughness can be easily located.

Three-dimensional measurement and inspection is an area with growing needs and interests in many domains, such as integrated circuits (IC), medical cure, and chemistry. Among the methods, broadband light interferometry is widely utilized due to its large measurement range, noncontact and high precision. In this paper, we propose a spatial modulation depth-based method to retrieve the surface topography through analyzing the characteristics of both frequency and spatial domains in the interferogram. Due to the characteristics of spatial modulation depth, the technique could effectively suppress the negative influences caused by light fluctuations and external disturbance. Both theory and experiments are elaborated to confirm that the proposed method can greatly improve the measurement stability and sensitivity with high precision. This technique can achieve a superior robustness with the potential to be applied in online topography measurement.

Alternative techniques for measurement of misalignment in a segmented mirror are of interest to the telescope community in the limit of large misalignment that precludes interferometric tracking. A variation of phase measuring deflectometry can be used to determine 5 degrees of freedom (DOF) of the misalignment with knowledge of the remaining 1 DOF. A camera and screen are positioned near the center of curvature, and the camera collects images of the screen pattern reflected from the mirror. In this application, the form of each segmented mirror is assumed known, so the misalignment contribution to the measurement can be determined. The approach is based on a Zernike analysis of distorted fringe patterns and the sensitivity to misalignment. We discuss simulation results in this paper.

Deflectometry has been proven as a high precision and high dynamic range surface metrology technique. We report on the use of deflectometry to diagnose mount-induced optical surface deformations. A surrogate mirror from the OLI-2 earthobserving satellite mission is tested with deflectometry in a non-null configuration using only a CCD camera and an LCD computer monitor. Moments are mechanically induced at each flight-like mirror mount and the deformed surface is measured. Systematic errors in the surface measurements are significantly reduced by maintaining a consistent measurement geometry and evaluating moment-induced deformations differentially. The surface deformation modes from orthogonal moments at each mirror mount are compared to FEA predictions. The agility of this metrology sets the groundwork for in situ measurements of flight aspheric mirror surface deformations during component integration and prior to system testing.

The testing technique with high dynamic range is required to meet the measurement of refractive wavefront with large distortion from test refractive surface. A general deflectometric method based on reverse Hartmann test is proposed to test refractive surfaces. Ray tracing of the modeled testing system is performed to reconstruct the refractive wavefront from test surface, in which computer-aided optimization of system geometry is performed to calibrate the geometrical error. For the refractive wavefront error with RMS 255 μm, the testing precision better than 0.5 μm is achieved.

In the fringe-illumination deflectometry based on reverse-Hartmann-test configuration, ray tracing of the modeled testing system is performed to reconstruct the test surface error. Careful calibration of system geometry is required to achieve high testing accuracy. To realize the high-precision surface testing with reverse Hartmann test, a computer-aided geometrical error calibration method is proposed. The aberrations corresponding to various geometrical errors are studied. With the aberration weights for various geometrical errors, the computer-aided optimization of system geometry with iterative ray tracing is carried out to calibration the geometrical error, and the accuracy in the order of subnanometer is achieved.

Annular sub-aperture stitching interferometry (ASSI) has provided an alternative solution to measure rotationally symmetric aspheric surfaces with low cost and high flexibility. It is an effective way to test the aspheric surface with a larger aperture and larger relative aperture without null compensation. In this paper, two kinds of annular sub-aperture stitching algorithms, pairwise sequential stitching (PSS) and global synchronously stitching (GSS), were studied. The detailed mathematical expressions are shown in the form of matrix. Besides, the influence of the noise and number of sub-apertures to the two algorithms was also studied by simulation. At last, experimental results of a convex hyperboloid surface by using the two stitching algorithms are presented.

Recently, the hypoxia imaging has been recognized as the advanced technique to detect cancers because of a strong relationship with the biological characterization of cancer. In previous studies, hypoxia imaging systems for endoscopic diagnosis have been developed. However, these imaging technologies using the visible light can observe only blood vessels in gastric mucous membrane. Therefore, they could not detect scirrhous gastric cancer which accounts for 10% of all gastric cancers and spreads rapidly into submucous membrane. To overcome this problem, we developed a measuring system of blood oxygen saturation in submucous membrane by using near-infrared (NIR) spectroscopy. NIR, which has high permeability for bio-tissues and high absorbency for hemoglobin, can image and observe blood vessels in submucous membrane. NIR system with LED lights and a CCD camera module was developed to image blood vessels. We measured blood oxygen saturation using the optical density ratio (ODR) of two wavelengths, based on Lambert-Beer law. To image blood vessel clearly and measure blood oxygen saturation accurately, we searched two optimum wavelengths by using a multilayer human gastric-like phantom which has same optical properties as human gastric one. By using Monte Carlo simulation of light propagation, we derived the relationship between the ODR and blood oxygen saturation and elucidated the influence of blood vessel depth on measuring blood oxygen saturation. The oxygen saturation measuring methodology was validated with experiments using our NIR system. Finally, it was confirmed that our system can detect oxygen saturation in various depth blood vessels accurately.

We describe patent pending fiber optic apparatus for measurements of thicknesses and distance employing low resolution spectrometer and etalon. The application of an additional known reference etalon "stretches fringes" and allows us to use Fabry Perot interference to investigate thick samples and large distances which would not be possible when using the low resolution spectrometer alone.

A diffraction grating is found at the heart of every modern spectrophotometer and yet, despite being used for over 60 years, a practical and efficient characterization tool has proven to be elusive. Part of the challenge can be attributed to the unique angular dependent geometry, or off axis dispersion, of gratings. Here we demonstrate automated grating efficiency measurements of four reflection gratings (300, 1200, 1800 and 3600 grooves per mm). Total measurement time was less than 2 hrs at a maximum of 161 wavelengths per grating. This approach can reduce test times or assist expand quality assurance, or design verification, programs. Automated measurements are performed in hours demonstrating efficiency and ease-of-use advantages when compared to equivalent manually operated systems.

This paper describes research that demonstrated gated, femtosecond, digital holography, enabling 3D microscopic viewing inside dense, almost opaque sprays, and providing a new and powerful diagnostics capability for viewing fuel atomization processes never seen before. The method works by exploiting the extremely short coherence and pulse length (approximately 30 micrometers in this implementation) provided by a femtosecond laser combined with digital holography to eliminate multiple and wide angle scattered light from particles surrounding the injection region, which normally obscures the image of interest. Photons that follow a path that differs in length by more than 30 micrometers from a straight path through the field to the sensor do not contribute to the holographic recording of photons that travel in a near straight path (ballistic and “snake” photons). To further enhance the method, off-axis digital holography was incorporated to enhance signal to noise ratio and image processing capability in reconstructed images by separating the conjugate images, which overlap and interfere in conventional in-line holography. This also enables digital holographic interferometry. Fundamental relationships and limitations were also examined. The project is a continuing collaboration between MetroLaser and the University of California, Irvine.

Recently most of the measurement tasks in industry, civil engineering and culture heritage applications require archiving, characterization and monitoring of 3D objects and structures and their performance under changing conditions. These requirements can be met if multimodal measurement (MM) strategy is applied. It rely on effective combining structured light method and 3D digital image correlation with laser scanning/ToF, thermal imaging, multispectral imaging and BDRF measurements. In the case of big size and/or complicated objects MM have to be combined with hierarchical or synthetic aperture (SA) measurements. The new solutions in MM and SA strategies are presented and their applicability is shown at interesting cultural heritage and civil engineering applications.

Schlieren imaging has been an essential method for studying aerodynamic effects, particularly thermal convection, shock waves, and turbulent flows. This paper describes a compact portable digital focusing schlieren system that can be used to visualize relatively large fields for applications in ventilation design and aerodynamics research. Visualizing large fields is difficult using classical schlieren systems that employ collimated light because their field of view is limited by the size of the mirrors or lenses. Background-oriented schlieren systems are well-suited for visualizing large fields, but their sensitivity is limited by the need to simultaneously maintain focus on the background pattern and the test area. Lens and grid-based focusing schlieren systems are essentially hybrids between classical and background-oriented systems. They can visualize fields that are much larger than possible with classical schlieren systems, while providing more sensitivity than background-oriented schlieren systems. Using commercially available camera lenses and optics, fields up to several square meters can be visualized. A key innovation in the system presented here is that digital display devices are used to display the background pattern, which simplifies the optical system and reduces its size. To calibrate the system, proprietary software is used to analyze images acquired by the system’s digital camera, and then a background pattern is computed that is complementary to the cutoff grid. The calibration software also provides real-time background subtraction and contrast enhancement. The schlieren system is portable enough that it can be set up quickly in industrial facilities.

When fringe projection profilometry is used for measuring rough/textured surfaces, the fidelity of the measurement is subject to the spatial frequency response. The instrument transfer function (ITF) is one appealing approach to characterize this property. The foundation of ITF analysis is based on the linear theory; only linear systems are appropriate for ITF analysis. A fringe projection system is intrinsically nonlinear, but it can be approximated as a linear system when certain conditions are met. Here we investigate the linear conditions of a custom fringe projection system designed for an additive manufacturing application. The applicability of ITF is discussed through mathematical analysis and simulations.

We demonstrated a three-dimensional (3D) dental scanning apparatus based on structured illumination. A liquid lens was used for tuning focus and a piezomotor stage was used for shift of structured light. A simple algorithm, which detects intensity modulation, was used to perform optical sectioning with structured illumination. We reconstructed 3D point cloud, which represents the 3D coordinates of the digitized surface, of a dental gypsum cast by piling up sectioned images. We performed 3D registration of individual 3D point cloud, which includes alignment and merging the 3D point clouds, to exhibit a 3D model of the dental cast.

In fringe projection technique, system calibration is a tedious task to establish the mapping relationship between the object depths and the fringe phases. Especially, it is not easy to accurately determine the parameters of the projector in this system, which may induce errors in the measurement results. To solve this problem, this paper proposes a new calibration by using the cross-ratio invariance in the system geometry for determining the phase-to-depth relations. In it, we analyze the epipolar eometry of the fringe projection system. On each epipolar plane, the depth variation along an incident ray induces the pixel movement along the epipolar line on the image plane of the camera. These depth variations and pixel movements can be connected by use of the projective transformations, under which condition the cross-ratio for each of them keeps invariant. Based on this fact, we suggest measuring the depth map by use of this cross-ratio invariance. Firstly, we shift the reference board in its perpendicular direction to three positions with known depths, and measure their phase maps as the reference phase maps; and secondly, when measuring an object, we calculate the object depth at each pixel by equating the cross-ratio of the depths to that of the corresponding pixels having the same phase on the image plane of the camera. This method is immune to the errors sourced from the projector, including the distortions both in the geometric shapes and in the intensity profiles of the projected fringe patterns.The experimental results demonstrate the proposed method to be feasible and valid.

Collimator is popular used in optical testing in laboratory to simulate target in a distance. Glass plate with pattern is fundamental constitute of collimator focal plane, which should be placed precisely with respect to its optics. For collimator in used or to be built, it is necessary to check position of its focal plane. We develop a fast method to check focal plane position with interferometer. Results derived from this method are compared with that derived from angle deviation measurement method. Meanwhile, focal plane adjustment of imaging telescope can be performed with same way.

By using a light-emitting diode as the probing light source and a Shack-Hartmann wave-front sensor to execute a relative measurement, we present a simple and sensitive method for measuring surface fluctuation of a nominally flat sample. We used an epitaxial wafer for test. The reflected wave front from the surface of the sample was first calibrated to be a planar surface. The surface fluctuation of the test sample could be estimated from the increment on the variance of the wave-front surface to its regression plane after the sample had been shifted by a small distance by using the Bienaymé formula.

The optical coherence tomography (OCT) is an optical imaging method, which is widely applied in variety applications. This technology is used to cross-sectional or surface imaging with high resolution in non-contact and non-destructive way. OCT is very useful in medical applications like ophthalmology, dermatology or dentistry, as well as beyond biomedical fields like stress mapping in polymers or protective coatings defects detection. Standard OCT imaging is based on intensity images which can visualize the inner structure of scattering devices. However, there is a number of extensions improving the OCT measurement abilities. The main of them are the polarization sensitive OCT (PS-OCT), Doppler enable OCT (D-OCT) or spectroscopic OCT (S-OCT). Our research activities have been focused on PS-OCT systems. The polarization sensitive analysis delivers an useful information about optical anisotropic properties of the evaluated sample. This kind of measurements is very important for inner stress monitoring or e.g. tissue recognition. Based on our research results and knowledge the standard PS-OCT provide only data about birefringence of the measured sample. However, based on the OCT measurements more information including depolarization and diattenuation might be obtained. In our work, the method based on Jones formalism are going to be presented. It is used to determine birefringence, dichroism and optic axis orientation of the tested sample. In this contribution the setup of the optical system, as well as tests results verifying the measurements abilities of the system are going to be presented. The brief discussion about the effectiveness and usefulness of this approach will be carried out.

In this paper, we propose and present verification of all-optical methods for stabilization of the end-to-end delay of an optical fiber link. These methods are verified for deployment within infrastructure for accurate time and stable frequency distribution, based on sharing of fibers with research and educational network carrying live data traffic. Methods range from path length control, through temperature conditioning method to transmit wavelength control. Attention is given to achieve continuous control for relatively broad range of delays. We summarize design rules for delay stabilization based on the character and the total delay jitter.

Phase unwrapping is a significant procedure that has raised a great interest in many coherent imaging systems. What we believe to be a new phase unwrapping algorithm, is described and tested. The method starts from the fact that 2D wrapped phase distribution can be regarded as a response to two orthogonal 1D direction excitation signals. This suggests a cepstrum analysis to be implemented in the phase unwrapping problem. Experimental results both from the fringe projection profilometry and DENSE MRI also confirmed the validity of our approach. In fact, this proposed method is possible to attain a fast and practical phase unwrapping solution with enhanced noise robustness.

A novel method for the measurement of vibration is proposed and demonstrated. The proposed experiment is based on laser triangulation: consists of line laser, object under test and a high speed camera remotely controlled by a software. Experiment involves launching a line-laser probe beam perpendicular to the axis of the vibrating object. The reflected probe beam is recorded by a high speed camera. The dynamic position of the line laser in camera plane is governed by the magnitude and frequency of the vibrating test-object. Using phase correlation technique the maximum distance travelled by the probe beam in CCD plane is measured in terms of pixels using MATLAB. An actual displacement of the object in mm is measured by calibration. Using displacement data with time, other vibration associated quantities such as acceleration, velocity and frequency are evaluated. The preliminary result of the proposed method is reported for acceleration from 1g to 3g, and from frequency 6Hz to 26Hz. The results are closely matching with its theoretical values. The advantage of the proposed method is that it is a non-destructive method and using phase correlation algorithm subpixel displacement in CCD plane can be measured with high accuracy.