This PDF file contains the front matter associated with SPIE Proceedings Volume 11189, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

In this paper, we propose a method for the structured-light field (SLF) 3D measurement, involving ray calibration and phase mapping. The ray calibration is carried out to determine each light ray with metric spatio-angular parameters. Base on the ray parametric equation, the phase mapping in the SLF is developed so that spatial coordinates could be directly mapped from phase-encoding information. Then, a calibration strategy is designed to determine the mapping coefficients for each light ray, achieving high-efficiency SLF 3D reconstruction.

Measurement of magnetic fields by monitoring the Larmor precession of atomic spins is commonly used nowadays because of the high sensitivity and absolute measurement. This paper proposes a novel atomic magnetometer based on the self-sustaining method for large and fluctuating magnetic fields. In combination with the indefinitely persist Larmor precession signal, the sensitivity of the magnetometer increases following a much faster τ^-1 rule beyond the atomic coherence lifetime. The maximum magnetic field have been experimentally demonstrated up to 40000 nT, the sensitivity achieved is 20 pT/√Hz and the frequency response bandwidth is 5 kHz, respectively. This magnetic field sensor is advantageous for applications requiring high sensitivity over a wide dynamic range such as geology and space physics.

As the advantages of high forming accuracy, fast material removal efficiency and slight machining defects, the ultraprecision grinding using micro-powder diamond wheel has been widely applied to the processing of large aperture and complex surface optical elements. Due to the brittleness and hardness of optical materials, micro-powder diamond wheel is easy to wear during grinding process, which affects the surface roughness and depth of sub-surface damage layer of components. In order to accurately characterize the wear state of diamond wheel in the grinding process, a method based on in-situ micro-observation of grinding wheel and abrasive particle image contour recognition was proposed to detect the diamond wheel. First, based on the grinding experiments, the surface micromorphology of grinding wheel was acquired by in-situ microscopic observation, and the wear forms of the grinding wheel were analyzed. Then the average distribution density of wear particles and average wear area were taken as the evaluation parameters of the wear state of the wheel. After outstanding the edge profile of abrasive particles by Laplacian enhancement operator and binary processing, the edge profiles of wear particles were extracted out. And by calculating the number and projection area of each wear abrasive particles, the average distribution density of wear particles and the average wear area in the measured region on the surface of grinding wheel were obtained. At the end, the wear state of resin bonded diamond grinding wheel used for grinding fused silica optics was tested. The experimental results showed that the diamond wheel states of initial wear stage and steady wear stage were accurately identified by the parameters of distribution density of wear abrasive particles and average wear area.

High-precision topography measurements of nearly flat specimens with nanometre uncertainty are still demanding. They are needed for synchrotron or other high-quality optical mirrors. At the Physikalisch-Technische Bundesanstalt (PTB), we operate an interferometric setup and a small-angle deflectometric setup for flatness measurement. We present both systems, show the measurement uncertainties and discuss the pros and cons of interferometric and gradient based measurement systems. To achieve the nanometre level in flatness metrology, the environmental conditions and the holder of the specimen are very important. We show measurements of topography changes due to delayed elasticity effects. We demonstrate current developments with the small-angle deflectometer, especially to improve the lateral resolution.

Scientific instruments and facilities used for calibrating the dynamic angle error of inertial instruments have played more and more important roles in mechanism error research and accuracy improvement. Present attitude measurement methods can not simultaneously meet the requirements of the inertial instrument angle error calibration in dynamic environments such as linear or angular vibration. Based on the collaborative integration and modeling calculation of single-point laser Doppler vibrometer, this paper proposes a dynamic attitude measurement system that can completely realize non-contact real-time accurate three-dimensional rotation angle measurement, filling in the blank of non-contact dynamic angle error calibration of inertial instrument. Besides, we propose a distance calibration method to reduce the angle measurement error from 0.34° to 0.0072°, which fully satisfies the non-contact measurement requirements of the inertial instrument.

Testing wavefront distortions at the design wavelength is critical for optical system qualification. Existing technologies and methods for measuring transmitted wavefronts typically operate at only a few specific wavelengths. In previous research, we propose a method for estimating the wavefront distortion of an optical transmission system in a broad bandwidth. We establish the relationship between the transmitted wavefront and wavelength, using Zernike fringe coefficients to represent the wavefront. We have also experimentally tested a single lens represents the monochromatic transmission system at four wavelengths with interferometers. The results show the monotonic Zernike-wavelength curves of in 400~1000nm bandwidth can be predicted by fitted Conrady formula with three data points. In this paper, we further test a doublet achromatic lens at five wavelengths with interferometers, and we find most Zernike-wavelength curves of the doublet achromatic lens are still monotonic, which can solved by binomial Conrady formula with two data points. Using three points to fit Conrady formula for part of monotonic curves is the same as using two points to solve binomial Conrady formula. However the Z8- wavelength curve which have an inflection point must solved by Conrady formula with three data points. The experimental results of achromatic system are more representative, it shows that Zernike-wavelength curve of achromatic system can be expressed by Conrady formula. In practice testing, if the wavefronts measuring at different wavelengths are accurate, the wavefront of arbitrarily wavelength in a certain band can be estimated by solving Conrady formula. Our experiment shows that the Conrady formula can represent the dispersion characteristics of some optical systems, especially for achromatic system. And the feasibility of measuring transmitted wavefront in a certain band based on Zernike coefficient is verified. The new method will help to simplify the process of multi-wavelength interferometric measurements.

The dual wavelength interferometry in digital holography can eliminate 2π ambiguities with a large synthetic wavelength, but the measurement error tends to be amplified. In this paper, a new numerical algorithm is proposed to reduce the amplification error, and further expand the measurement range. The wrapped phase map associated with one wavelength is used to assist unwrapping the phase map associated with the other wavelength. Since these two phase maps correspond to the same step height, an exhaustive searching method is applied. The measurement error will not be amplified linearly with the synthetic wavelength, but controlled at the same level with the single wavelength interferometry. In consideration of the measurement errors such as the environmental vibration, instability of wavelength and so on, a tolerance is set to guarantee the stability of the solution. The performance and feasibility of the proposed algorithm is verified by the numerical demonstration.

As the digital projector develops, fringe projection profilometry has been widely used in the fast 3D measurement. However, the field of view of traditional 3D measurement systems is commonly in decimeters, which limits the 3D reconstruction accuracy to tens of microns. If we want to improve the accuracy further, we have to minimize the field of view and meanwhile increase the fringe density in space. For this purpose, we developed two kinds of systems based on a stereo-microscope and telecentric lenses, respectively. We also studied the corresponding calibration frameworks and developed fast 3D measurement methods with both Fourier transform and phase- shifting algorithms for real-time 3D reconstruction of micro-scale objects.

The multi-frequency temporal phase unwrapping (MF-TPU) method, as a classical phase unwrapping algorithm for fringe projection profilometry (FPP), is capable of eliminating the phase ambiguities even in the presence of surface discontinuities or spatially isolated objects. For the simplest and most efficient case, two sets of 3-step phase-shifting fringe patterns are used: the high-frequency one is for 3D measurement and the unit-frequency one is for unwrapping the phase obtained from the high-frequency pattern set. The final measurement precision or sensitivity is determined by the number of fringes used within the high-frequency pattern, under the precondition that the phase can be successfully unwrapped without triggering the fringe order error. Consequently, in order to guarantee a reasonable unwrapping success rate, the fringe number (or period number) of the high-frequency fringe patterns is generally restricted to about 16, resulting in limited measurement accuracy. On the other hand, using additional intermediate sets of fringe patterns can unwrap the phase with higher frequency, but at the expense of a prolonged pattern sequence. Inspired by recent successes of deep learning techniques for computer vision and computational imaging, in this work, we report that the deep neural networks can learn to perform TPU after appropriate training, as called deep-learning based temporal phase unwrapping (DL-TPU), which can substantially improve the unwrapping reliability compared with MF-TPU. We further experimentally demonstrate for the first time, to our knowledge, that the high-frequency phase obtained from 64-period 3-step phase-shifting fringe patterns can be directly and reliably unwrapped from one unit-frequency phase using DLTPU. These results highlight that challenging issues in optical metrology can be potentially overcome through machine learning, opening new avenues to design powerful and extremely accurate high-speed 3D imaging systems ubiquitous in nowadays science, industry, and multimedia.

In this paper, we propose a high-speed three dimensional (3D) shape measurement with the multi-view system using deep learning. Common stereo matching methods are based on block-matching or graph cuts to build the global correspondence of stereo images and obtain the dense disparity map. For fringe projection profilometry (FPP), a large number of stereo matching algorithms have been proposed to enhance the accuracy and computational efficiency of stereo matching and acquire the disparity map with sub-pixel precision by using phase constraint, geometric constraint, and depth constraint. However, the universality and precision of these methods are still not enough which is difficult to meet high-precision and high-efficient 3D measurement applications. Inspired by deep learning techniques, we demonstrate that the deep neural networks can learn to perform stereo matching after appropriate training, which substantially improves the reliability and efficiency of stereo matching compared with the traditional approach. Besides, to acquire 3D results with high performance, the optimal design of the patterns projected by the projector is discussed in detail, and the relative spatial positions between the cameras and the projector are carefully adjusted in our multi-view system. Experimental results demonstrate the stereo matching method using deep learning provides better matching efficiency to realize the absolute 3D measurement for objects with complex surfaces.

Conformal coating is a protective coating widely used in printed circuit boards (PCBs), protecting PCBs from harsh environmental conditions. Its curing extent and thickness are the key factors, determining its protection performance. At present, the traditional method to evaluate the curing extent is metallographic section, which cuts PCB and images its cross-section under a microscope. However, it is destructive. In this study, we proposed to use optical coherence tomography (OCT) to evaluate the coating curing extent. Note that Brownian motion inside the conformal coating gets slower during curing process, leading to a smaller OCT intensity variation over time. Therefore, speckle variance (SV) of OCT imaging, which actually measures the OCT intensity variation, is expected to become smaller during the curing process and can be used to evaluate the curing extent over the whole imaging depth. To demonstrate the capability of SVOCT in detecting the curing extent of conformal coating, multiple OCT images were acquired at each curing status for SV calculation. The results show that the speckle variance of OCT image will gradually decrease during the curing process of conformal coating and eventually stabilize after the coating cures completely. This can be utilized to assess the curing extent of the conformal coating.

In this work, we consider the problem of 3D shape reconstruction with a system with two cameras and one projector, which can be regarded as a composite system with two fringe projection profilometry (FPP) systems and one stereo vision (SV) system. Different from the active SV systems in the literature where FPP is used to assist SV to address the issue of corresponding matching, a new system is proposed in this paper by constructing a fusion cost function with the consideration of both FPP and SV triangulations, so that the measurements of the two cameras can be fused to achieve better measurement performance than that of the active SV and FPP. In addition, a message passing algorithm for 3D shape reconstruction with the system is developed by using the new cost function and exploiting the unknown correlation of object surfaces. Simulation results demonstrate that the proposed system can achieve considerable performance gain.

In recent years, water quality testing has become an increasingly important topic. Compared with some common water quality identification methods, this study proposes a new method for identifying water samples in UV-visible spectroscopy. In this study, the UV-visible spectra of water samples from two different regions of tianchi and shuimogou in Urumqi were measured, and the pattern recognition algorithm was used to identify the two types of water samples. The acquired UV-visible spectra of water samples were extracted from 80 original high-dimensional spectral data by Partial Least Squares Regression (PLS), and the extracted features were modeled and classified by Support Vector Machine (SVM) classifier. The parameters C and g are optimized by Grid Searching (GS). The classification accuracy of the tianchi water sample and the water mill ditch water sample was 100%. The results of this study illustrate the great potential for rapid detection of water samples using UV-visible spectroscopy in the future.

The International Thermonuclear Experimental Reactor (ITER) Project is the next step in the transition from experimental studies of plasma physics to full-scale electricity-producing fusion power stations. There is a need for the regular measuring of the erosion and deposition at the wall once the reactor starts operating. An erosion and deposition monitor able to measure the changes in the surface shape is planned. We have shown that long distance shape measurements in challenging environmental conditions (strong vibrations) can be done by two-wavelength digital holography and thus this technique could be used for the erosion monitoring inside the ITER-Tokamak.

Silver ions cannot exist in excess in the human body. Conventional instrumental analysis methods such as atomic emission and atomic absorption are commonly used to detect Ag ⁺, but the sensitivity is not satisfactory. Therefore, we developed a novel surface-enhanced Raman scattering (SERS) substrate with a single-layer porous silicon structure, and we completed the detection of Ag ⁺ in domestic water and food based on this substrate. The SERS substrate with porous silicon structure has high detection sensitivity. It is found that Ag ⁺ can be oxidized and deposited on porous silicon to change the Raman spectral properties. The results show that the Raman spectral intensity is linearly related to different content of silver ions, and the maximum linear correlation coefficient is 0.95123. The exploratory research results prove that the newly prepared SERS substrate with single-layer porous silicon is has great significance for the detection of water source and food safety.

Accurate and traceable reference coordinates in three-dimensional space is the key and difficult point for coordinate calibration of large-scale measurement instruments such as laser tracker and iGPS. This paper studies the application of multilateration with laser tracker in establishing reference coordinates. First, a reference coordinate network is established, which has good spatial scalability and is compatible with multiple targets. Then, multilateration with laser tracker is applied to calibrate the reference coordinate network. And the basic principle, measurement uncertainty evaluation and tracker layout optimization are studied in detail. So that the reference coordinates are traced to the laser interference. Finally, through the repeatability test, length test, and coordinate test, it is shown that the reference coordinates satisfy their measurement uncertainty range and can be used for coordinate calibration of the large-scale measurement instruments.

Arsenic (As) is a trace element exist in the environment, and it is one of the common poisonous elements in water, excessive intake of arsenic can cause great damage to human body. At present, mainly used laboratory detection methods of arsenic such as electrochemical method, ion chromatography, atomic absorption spectroscopy and so on, can detective arsenic, but these techniques have some problems such as low sensitivity, intractable operation and expensive. Based on the specific molecules of arsenic, we tested a new rapid detection method of arsenic solution, we prepared surface-enhanced Raman enhanced scattering substrate (SERS substrate) to complete the detection of arsenic solution. Through linear discriminant analysis, the result show that Raman spectrum has high specificity and sensitivity. The study indicated the feasibility of using SERS substrate to conduct Raman spectrum detection on arsenic, which was of great significance for the detection of arsenic in aqueous solution.

Film thickness is an important geometric parameter in semiconductor technology, and the accuracy of its magnitude affects directly the overall performance of the device. In order to accurately control and characterize the film thickness parameters, a set of 2nm~1000nm SiO₂ film thickness standards were developed to carry out measurement technology research. Firstly, a method of growing SiO₂ on pure Si wafer by a thermal oxidation process was used to develop a standard sample of the film thickness, and to evaluate the uniformity and stability. Secondly, the measurement model and method were studied, and the thickness of the film was characterized, based on the spectral ellipsometer. Finally, the uncertainty of measurement results to the standard are evaluated, based on the MCM simulation method. The results show that the uniformity of film thickness is better than 0.3nm, the stability is better than 0.2nm, and the uncertainty is 0.4nm~1.4nm, k=2.

Structured light three-dimensional (3D) measurement techniques have obtained increasing popularity in the field of industrial automation, inverse engineering, and graphics. Recent literatures show that the imperfect of the imaging system in the structured light 3D metrology will cause the discontinuous-induced measurement artifact (DMA) in the area around the discontinuous edge. Existing DMA reduction methods need to detect the all edges accurately first. This procedure is hard to accomplish when the edges are defocused. Meanwhile, the corrected date in the error area relies heavily on the data in its nearest unaffected area, which makes the corrected data unreliable in some situations. In this work, a flexible deconvolution-based method is proposed to solve the above two problems in this paper. Simulation and experiment show that our proposed method can reduce the Root Mean Square phase/height error of DMA by up to 4 times.

Aiming at the disadvantage of small diameter, low efficiency, poor accuracy and can only measure sub-aperture of traditional contact surface shape measurement method to detect grinding optics surface, this paper uses non-contact laser displacement sensor, and proposes an in-situ measurement method to measure full-aperture surface of grinding optics, it has the characteristics of high measurement efficiency, high accuracy, large measurement aperture and the ability to measure full-aperture surface. This method is in-situ measurement, so it can measure full-aperture surface of optics with arbitrary aperture and shape after rough grinding, semi-precision grinding and fine grinding. Orthogonal co-directional grating measurement path can effectively avoid the influence of machine backlash. Therefore, the optics can be directly compensated according to the results of surface measurement, so that the surface of optics can meet the requirements. After the measurement is completed, a set of orthogonal measurement data are obtained, and the invalid data are manually clipped. Linear interpolation, nearest neighbor interpolation and cubic spline interpolation are used to interpolate the clipped data, and the orthogonal data are superimposed to obtain the final shape. The validity of this method is verified by the sub-aperture surface detection method, experiments show that the optimal surface measurement results can be obtained by cubic interpolation for both planar and aspheric optics. Using this method to compensate the grinding of 530mm×530mm 2-D off-axis aspheric optics, the full-aperture surface shape accuracy PV is better than 3.5μm.

With the fast development of integrated circuits, photovoltaics, automobile industry, advanced manufacturing, and astronomy, it is particularly important to obtain the three-dimensional (3D) shape data of specular objects quickly and accurately. Owing to the advantages of large dynamic range, non-contact operation, full-field and fast acquisition, high accuracy, and automatic data processing, phase-measuring deflectometry (PMD, also called fringe reflection profilometry) has been widely studied and applied in many fields. Direct PMD (DPMD) can directly establish the relationship between phase and depth data without gradient integration process, so it can be used for 3D shape measurement of specular objects having discontinuous surfaces. However, compared with gradient data, depth data is more sensitive to measurement noise, so the measurement accuracy obtained by gradient field integration is higher. In order to make use of the anti-noise property of gradient measurement structure, some PMD techniques usually abandon the height data obtained from the intermediate process and use the gradient data to complete the surface reconstruction. Stereo deflectometry is a typical representative to retrieve 3D shape of the measured object according to the gradient integration. It calculates the gradient field based on the uniqueness of the normal vector of the object points by using two cameras. Although obtaining high-precision measurement results, this method cannot be used for the measurement of discontinuous objects. In this paper, a new stereo DPMD method is proposed to obtain 3D shape of specular objects having discontinuous surfaces. Some experimental results on measuring discontinuous specular objects verify the high precision of the proposed stereo DPMD method.

An overview is provided of the non-contact measurement of surface morphology, focusing on form and roughness. Existing methods considered include con-focal scanning methods for the evaluation of large-scale surfaces where comparisons are drawn with direct areal measurements where data stitching is required to provide coverage of large scale surfaces. The applications of large-scale surfaces presented include, free form dental metrology, paleontology and early cylindrical mechanical sound recordings. Data registration of free form surfaces is presented to determine low scale wear of dental surfaces. For the new directions, consideration is given to the application of precision X-ray computer tomography, to determine free form surfaces and applied to the dental surfaces. The results show that the con-focal method remains the best solution for complex free form surfaces and that the XCT systems while offering some advantages require further research for full application.

The fringe projection technique is an effective technique to measure 3D shape of objects, in which phase retrieval is an important procedure. In this paper, the phase extraction algorithm of random phase-shift, which can be used in the fluctuating light source and the non-uniform background intensity and modulation amplitude, is proposed. The proposed method can retain more details of reconstructed phase than Fourier transform profilometry. Compared with multi-frame phase-shifting method, the proposed method only needs two fringe patterns to extract the phase and phase shift of the object. Our method consists of two stages. Firstly, the method is built based upon Lissajous Ellipse Fitting technique that extracts the phase from only two phase-shifted fringes which may contain arbitrary and unknown phase shift in dynamic measurement experiment. Second, the non-uniform background intensity and modulation amplitude are removed. The simulation results demonstrate that the proposed method can effectively obtain the phase.

Phase unwrapping is an essential step for 3D shape measurement based on fringe projection. Temporal phase unwrapping methods can be implemented by analyzing the multiple patterns that encode the fringe order information. They can retrieve the fringe orders on a pixel-by-pixel basis and are less prone to error propagation compared with spatial methods. However, fringe orders errors may still occur due to noise, reflectivity fluctuation and discontinuity of the object surface. Such errors may exhibit an impulsive nature and result in significant error to the recovered absolute phase map. This has been exploited by several methods to correct the fringe order errors, e.g., by filtering the fringe order sequences in a line-by-line manner. In this paper, a new method is proposed to correct the errors associated with fringe orders for the temporal phase unwrapping. The scheme first makes use of the low-rankness property of the fringe order map and sparse nature of the impulsive fringe order errors to more effectively remove the impulsive errors by applying robust principal component analysis (RPCA) algorithm. Then the smoothness of the two-dimensional unwrapped phase map is examined and the residual fringe order errors are detected based on a discontinuity measure of the phase map and corrected by comparing phase difference between two adjacent pixels in the unwrapped phase. The effectiveness of the proposed method is demonstrated via numerical experiments.

Nowadays, the speed of ultra-fast photography can exceed one quadrillion. However, it can record only two-dimensional images which lack the depth information, greatly limiting our ability to perceive and to understand the complex real-world objects. Inspired by recent successes of deep learning methods in computer vision, we present a novel high-speed three-dimensional (3D) surface imaging approach named micro deep learning profilometry (μDLP) using the structured light illumination. With a properly trained deep neural network, the phase information is predicted from a single fringe image and then can be converted into the 3D shape. Our experiments demonstrate that μDLP can faithfully retrieve the geometry of dynamic objects at 20,000 frames per second. Moreover, comparative results show that μDLP has superior performance in terms of the phase accuracy, reconstruction efficiency, and the ease of implementation over widely used Fourier-transform-based fast 3D imaging techniques, verifying that μDLP is a powerful high-speed 3D surface imaging approach.

Phase shifting profilometry (PSP) is considered as an effective method for 3D shape measurement based on fringe projection. However, PSP is not suitable for dynamic measurement, as it requires that the object be kept still. Movement of the object during the cause of projection of multiple fringe patterns may lead to significant error in the measurement of the 3D shape. A number of approaches were proposed to combat this problem consisting of two steps: Capturing of the movement and then compensation (or correction) of fringe patterns. However, such compensation is only valid for the cases where the object moves or rotates in the way that all points on the object surface change by the same amount. In other words, there is still not a method effective for measuring objects moving in a free 3D space. In this paper, a new method is proposed to combat the problem. Firstly, movement of the object is capturing by means of existing methods, yielding rotation matrix and translation vector, able to characterize arbitrary movement in a 3D space. Secondly, variation of the fringe patterns by the movement is analyzed and formulated, leading to the expressions of phase maps. Based on these expressions, a new method is proposed to compensate the variance on height map, with which PSP can be used to yield improved measurement performance. Computer simulations is carried out to verify the effectiveness of the proposed method.

Optical encryption system is generally vulnerable to attacks based on phase retrieval algorithm. In this paper, an improved encryption scheme is proposed based on the coherent 4-f system and complementary masks. This pair of irregular shaped complementary masks are introduced to cut the ciphertext and regroup them. The stitched ciphertext has high immunity to ciphertext attacks based on phase retrieval algorithms. We have done numerically simulation to demonstrate the feasibility and validity of the proposed technique.

With the development of optical manufacturing and measurement methods, precision optical elements are used extensively in various fields. As the beam scattering and energy loss caused by the surface defects of optical elements will reduce the lifetime of optical elements and the performance of optical systems, it is important to detect and evaluate the surface defects. However, several technical challenges remain in the surface defect detection of spherical optical elements. In this paper, a spherical defect detection experiment based on the dark-field imaging principle is proposed. The surfaces of two convex spherical optical elements are detected. Meanwhile, the illumination module is improved through experiments. The experimental results are compared with those of a white light interferometer, thereby demonstrating the validity of the method.

When polarized white-color light beams are allowed to travel in an optically active material, coloration of the polarized light beams can be observed due to optical rotation phenomena of the material. If prediction of colors to be observed becomes possible, it will be advantageous for the purpose of investigations of the material. The authors previously succeeded in establishing a theoretical mathematical expression for realizing predictions of changes in the angle of rotation as well as resultant changes in visible colors of polarized white-color light beams transmitting in sugared water as an optically active material. In this study, for the purpose of confirming whether the mathematical expression is applicable for any other optically active materials, commercially available syrup was employed as the optically active material. The angle of rotation was first determined through measurements, and visible colors of transmitted light beams were observed. In addition, the spectra of transmitted light beams were also measured. On the other hand, the changes in visible colors were predicted by employing the authors’ mathematical expression. As a result, roughly satisfactory matchings were confirmed between the actually measured or observed results and the predictions. Thus, the mathematical expression is believed to be applicable for investigations of any other optically active materials. Such predictions in color changes will be advantageous in science and engineering education.

A flexible calibration method with high precision was proposed for calibration of structured laser triangulation in the applications of 3D reconstruction and point cloud processing. The camera coordinate system was chosen as the ultimate reference coordinate. In this calibration process, be required only a planar pattern placed at different orientations and positions for obtainment of the camera intrinsic parameters. And then two or more non-coplanar sets of three collinear points were calculated for the laser projection plane coefficients. A line laser triangulation measurement system is established, consisted of laser diode, cylindrical lens module and camera imaging system. Experimental results based on the constructed structured laser triangulation system revealed that accuracy of the profile measurement is less than ±0.005mm, which can meet the majority of industrial inspection applications.

Conventional chemical methods to detect pesticide residue are complex, and need professional instruments as well as much time. NIR spectral analysis provides an effective way for pesticide residue detection because of simple operation, rapid analysis and non-destruction of samples. However, conventional calibration models are only effective after spectra were measured, and different models are needed for different instruments. In this study, we propose a novel calibration transfer method by using sequential forward selection to transfer calibration models between different crops and instruments. The calibration model built by master instrument can identify three kinds of pesticide including Chlorothalonil, Chlorpyrifos and Buprofezin. Spectra obtained by slave instrument can also be predicted by the models with the method. The experiment results show that the prediction accuracies increased from 50% up to 80% by using our method.

Based on photogrammetry, antenna deformation measurement in vacuum and cryogenic environment has been widely carried out. The strength of measuring network will affect the accuracy, repeatability and stability of the measured results. A method for evaluating the strength of photogrammetric network based on attenuation factor is proposed, that is, a strong correlation is established between the measurement accuracy and spatial network parameters through the formula of attenuation factor of network strength ,according to the factor value, the network layout can be evaluated . In this paper, the reliability of this method is verified by experiments. The method can obtain a better network design before measurement and avoid a lot of repetitive work. The evaluation method is applied to deformation measurement test for large aperture antenna in the vacuum and cryogenic environment .Thus reduces the test cost and the risk, enhances the measurement accuracy and the stability.

The complex components often require a variety of processes in the manufacturing process, such as turning, milling, grinding, polishing etc. Therefore, it is inevitable to produce defect features on the surface of the component. The defective surfaces will directly affect the performance of the entire component, so it must be identified during production and inspection. In this paper, based on the excellent curve feature recognition and sparse representation of curvelet transform, a defect extraction method based on the curvelet transform for feature separation in transform domain is proposed. The effectiveness of the method is proved by simulation results and experimental examples.

The absolute measurement of infrared spectral radiance is very important for optical radiometry. In this paper, a system for absolute measurement of infrared spectral radiance is built up. The system consists of fixed-point blackbody sources, a variable temperature blackbody, a radiant source to be measured, Fourier Transform Infrared Radiometer (FTIR), relay optical system, non-contact infrared thermometer and so on. The emissivity of the variable temperature blackbody is 0.999; the temperature range is 50°C ~ 1050°C. The emissivity of the radiant source to be measured is larger than 0.995; the temperature range is 30°C ~ 550°C. The variable temperature blackbody source was calibrated and can be traced to the fixed-point blackbody source. In experiment, it was used as the standard radiant source. The spectral range of this system is 3 μm ~ 14 μm. A serial of experiments have been implemented to analyze the uncertainty of each component, including the repeatability, size-of-source effect, stability, uniformity and so on. To improve the system’s uncertainty, we have suppressed stray radiation and optimized optical system by installing a water-cooled aperture and a field stop at the entrance of the optical system and before the FTIR, respectively; optimizing the system based on optical simulation and replacing the reflective mirrors with one off-axis parabolic mirror. Next step, we will re-evaluate the uncertainty of the improved system.

This paper presents a novel algorithm for partial reconstruction of the phase of an interference pattern. In multi-pulse train interferometers, the exact determination of the zero crossing position of the phase of interference fringes is important. The proposed algorithm is based on the chirp Z-transform instead of discrete Fourier transform and avoids the estimation of the whole wrapped phase of the interference pattern. In addition, to the best of our knowledge, this is the first reported method for partial reconstruction of the wrapped phase for interference fringe analysis in a pulse-train interferometer.

The traditional differential absorption spectroscopy method has simple detection principle for H₂S gas concentration detection, accurate detection and fast reaction speed, but it will produce large errors in low concentration and short optical path environment. Differential absorption spectroscopy requires a very complex super-definite equation to solve for concentration, which is easy to generate solution errors. Based on the traditional differential absorption algorithm, this paper uses genetic algorithm to invert low-concentration H₂S gas, but the genetic algorithm is prone to premature convergence and thus falls into local optimum. A genetic algorithm based on catastrophe optimization is designed to retrieve H₂S gas concentration. The use of catastrophic will significantly improve the ability of the algorithm to develop in the solution space. By preserving the local optimal solution obtained before the disaster, the algorithm can be avoided as a random search, which ensures the stability of the algorithm. The optimization of the differential absorption algorithm mainly includes data acquisition, data processing and data presentation. Data acquisition is the collection of changes that occur after gas molecules absorb photons. Data processing is based on the collected data and the optimization algorithm to calculate the optimal concentration. The data presentation is to display the calculated concentration on the computer. The concentration of H₂S gas was inversed by the traditional DOAS algorithm and the optimized DOAS algorithm. The results were compared. The results show that the method has high measurement accuracy for low concentration H₂S gas, and combines with traditional differential absorption spectroscopy to obtain a wider measurement range.

In this paper, based on the analysis of the shortcomings of three-point comparison odor bag method, gas chromatography method and gas sensor, a malodorous gas monitoring device based on differential optical absorption spectroscopy (DOAS) is designed. This paper focuses on testing six gases, including carbon disulfide, styrene, dimethyl disulfide and so on. The total length of the optical path is 60cm. When the standard deviation is twice, the detection limit of these gases is around 0.10ppm. The results of mixed malodorous by measured show that the interference between components is very small, and the relative error of each component is less than 3% of the full scale by least square method. The odor gas emission monitoring device based on DOAS technology designed in this paper has the advantages of simple device and high measurement accuracy, which can meet the application requirements of field measurement.

This paper describes a set of ultra-low smoke emission monitoring optical devices based on differential absorption spectroscopy (DOAS), which mainly includes a xenon lamp source, a sample cell, a spectrometer for light detection, and a Y-type optical fiber. The device utilizes a newly developed ultraviolet long path gas chamber, the energy of the ultraviolet spectrum is high, and the energy of the xenon lamp in the experiment is only enough to meet the application requirements. As well, based on DOAS optical device it has the advantages of high ultraviolet energy, small volume and high measurement accuracy. Therefore, the system solves the difficult problem of low concentration flue gas emission monitoring. The lower limit of detection of SO₂, NO and NO₂ concentration was 0.21 mg/m³, 0.13 mg/m³ and 0.61 mg/m³, respectively. Comparison of on-site field monitoring with high temperature FTIR (Fourier Transform Infrared Spectroscopy) flue gas emission monitor, the average concentrations of SO₂, NO and NO₂ measured by the two instruments were less than 14 mg/m³, 39 mg/m³ and 25 mg/m³ respectively, and the correlations were all above 0.995.

As one of the main indicators for characterizing the quality of a corrugated plate, the accurate acquisition of corrugation height is great important for guaranteeing the safety operation of heat exchangers. However, the traditional metrologies could not satisfy the measurement requirements of high precision and real-time due to the complex surface morphology of corrugated plate. In this paper, a preliminary study of application of the laser displacement sensor to the automatic on-line measurement of the corrugation height has been verified experimentally. To improve the measurement accuracy and efficiency, the data processing is divided into two parts: the measuring error analysis and the data fitting. An empirical correction model is established on the evaluation test to correct the errors caused by the incident angle at each measurement point. After that, by giving a segmentation to the cross sectional data from the geometrical characteristics of measured plate, the regression models of each interval data are established by the Least Square Method. Finally, the corrugation height of each subsection interval can be estimated from the difference between the minimum and maximum depth of each piecewise regression model. The experimental results demonstrate that our proposed metrology can improve the measuring speed effectively and is suitable to the practical measurement occasion.

Tunable Diode Laser Absorption Spectroscopy (TDLAS) applies optical method to realize fast and non-contact detection. This technology has the advantages of high resolution and high sensibility, and been widely employed in atmosphere environment detection in recent years. This paper mainly introduces how TDLAS is applied to detect the vehicle exhaust, to determine the content of CO, CO₂, NO and alkanes etc. Firstly, the principle of TDLAS is Lambert-Beer's law. It is based on the specific spectral "fingerprint" characteristics of different gases to detect the gas composition. In the same time, the light intensity is attenuated by molecular absorption, which is used to accurately analyze the density of gas. There are two ways to achieve. One is direct-absorption way, whose configuration and signal processing are simple, results have no need to be demarcated. The other is wavelength-modulation way, which has high resolution and low threshold. The selection of absorption spectral line needs not only to adapt the central wavelength of laser and responding wavelength of detector, but also to avoid the crossed spectral line of different gas to improve the precision of detection. Secondly, TDLAS system includes three parts, which are signal generation, signal detection and signal processing. Finally, TDLAS is compared with other spectral detection technologies in the aspect of sensitivity, character of working, applicable kinds of gas, in order to highlight the application scope of each technology.

An additional phase shift is produced when the 3D shape of dynamic scene is measured by phase shifting method. The phase distribution measured by traditional method is distorted and the recovered 3D shape is distorted as well. The Gerchberg iteration algorithm and the windowed Fourier assisted phase shifting method were proposed to reduce the distortion. The main ideal of these methods is to accurately estimate the phase shift between two fringe patterns. The accuracy of phase shift estimation is low near the edge where the frequency of fringe changes suddenly. We proposed a method to increase the accuracy of phase shift estimation. The edge of frequency sudden change is found out and then the fringe pattern is divided into different regions. The Gerchberg iteration algorithm is adopted to extend the fringe to outside of every region. The windowed Fourier analysis is adopted to estimate phase of every region and then the phase distribution of whole pattern is obtained. The phase shift between two fringe patterns is obtained by subtracting the estimated phase of first pattern from that of second pattern. Finally, the accurate phase distribution is obtained from the fringe patterns and the estimated phase shifts by least square method. The comparative experiments were carried out to evaluate the proposed method. The experimental results show that the accuracy of measured phase by proposed method is higher than that by windowed Fourier assisted phase shifting method.

In the 3D measurement system based on light-source-stepping method, phase shift changes with the depth of the object changes. The phase distribution recovered by N-step phase shifting method is distorted and then the recovered 3D shape is distorted. Fujigaki proposed the whole-space tabulation method to obtain 3D shape without distortion. The moving stage is used to calibrate the system and then the whole-space look-up tables are constructed. It is inconvenient to calibrate the measurement system. We proposed a new method to calibrate the system without moving stage. Firstly, the camera is calibrated by Zhang’s method. Secondly, a reference plane with sparse marks is placed at different depth of measurement volume. The fringes are projected on the plane and the images are captured at the same time. Thirdly, the phase of different depth is worked out by improved Fourier transform profilometry method. The phase of marker is estimated by local curve fitting. The image coordinates of markers are detected. The projection matrix from reference plane to image plane is worked out from the image coordinates and world coordinates of markers and the inner parameters of camera. The 3D coordinates of every pixel of reference plane are worked out from their image coordinates and the projection matrix. Fourthly, a whole-space look-up table is constructed. This method does not need precise moving stage to calibrate the relationship between phase and 3D coordinates. The hardware requirement for system calibration is simplified. Experiments are carried out to verify the proposed method.

Optical coherence tomography (OCT) is a non-destructive and non-contact sensing tool for imaging optical scattering media with microscopic spatial resolution. According to its imaging mechanism, this technology is very suitable for imaging and thickness measurement of multilayer structures. Thus, OCT has been widely used for medical diagnostics and non-destructive inspection in industries. However, due to the limited imaging depth, OCT can only be used for non-opaque materials. In this study, we developed a novel technique based on OCT imaging for thickness measurement of opaque materials. To demonstrate the ability of the technique, we obtained a double side view by establishing two symmetrical sample beams based on a home-built 1060nm swept source OCT system. Using the OCT system we developed, we can collect two surface contour information for non-transparent materials, and eventually calculate the thickness of the nontransparent material. The results show that the developed system keeps the imaging capability of OCT and further extend for opaque material thickness measurement.

We developed a color Ronchi pattern, a new form of fringe pattern, that can effectively used in fringe projection profilometry. The pattern is formed such that color channels red, green and blue are in separate spatial domains. From a single-shot image of the structured pattern, we are able to reconstruct the surface profile of a distorted paint canvas using both Fourier transform profilometry (FTP) and phase shifting profilometry (PSP). From the three surface reconstructions obtained using FTP, tiny artifacts in the form of ripples are observed. These artifacts are significantly reduced when the surface measurements in FTP are averaged. Experimental results have shown that both FTP and PSP successfully reconstructed the profile of a distorted paint canvas with a measurement difference between 10.00% to 15.00% from the actual displacement.

LED light sources are replacing incandescent lamps gradually and inevitable, but using traditional incandescent lamps as standard lamps to measure LED light sources introduces greater uncertainty due to the great difference of their spectrum. In order to reduce the measurement uncertainty, a standard lamp based on LED filament is developed. The lamp is free of cumbersome cooling devices, and its luminous intensity distribution is uniform in 4π geometry. However, its luminous flux is sensitive to the ambient temperature. Therefore, a linear model of luminous flux as a function of ambient temperature and the lamp voltage is established. Then driven by a constant current, the lamp voltage, the relative luminous flux and the ambient temperature of the LED standard lamp are monitored. The model parameters can be obtained from the test data. Finally, by measuring the lamp voltage, the luminous flux drift caused by the ambient temperature can be compensated, so that the luminous flux of the LED standard lamp maintains a stable magnitude.

In this paper, we propose a single-shot 3D shape measurement with spatial frequency multiplexing using deep learning. Fourier transform profilometry (FTP) is highly suitable for dynamic 3D acquisition and can provide the phase map using a single fringe pattern. However, it suffers from the spectrum overlapping problem which limits its measurement quality and precludes the recovery of the fine details of complex surfaces. Furthermore, FTP adopts the arctangent function ranging between -π and Π for phase calculation, which results in phase ambiguities in the wrapped phase map with 2π phase jumps. Inspired by deep learning techniques, in this study, we use a deep neural network to extract the phase information of the object from one deformed fringe pattern. Meanwhile, we design a dual-frequency fringe pattern with spatial frequency multiplexing to eliminate the phase ambiguities. Therefore, an absolute phase map can be obtained without projecting any additional patterns. The experimental results demonstrate that the single-shot 3D measurement method based on deep learning techniques can effectively realize the absolute 3D measurement with one fringe image and improve the measurement accuracy compared with the traditional Fourier transform profilometry.

In the ultrasound field, the parameters of the therapeutic sound field can’t trace to the source, or be directly measured. In order to solve this problem, this paper builds a system to obtain high-intensity focusing ultrasound pressure and detect sound field. High-intensity ultrasound pressure is detected directly by laser scanning technology. This technology overcomes the disadvantages of needlelike or thin-film hydrophone, whose tolerance is low, invasive detection influences the ultrasound field, and limited size brings the amendment average effect. Firstly, the general principle to measure the ultrasound pressure is proposed. The optical interference method is adopted to put a thin film coated with gold into the ultrasound field. When the thickness of the thin film is much smaller than the wavelength of the ultrasound, the vibration velocity of the thin film can be obtained by laser vibrometer, then the sound pressure of the same position can be calculated accordingly. Secondly, the configuration of the system is clearly shown, including the hardware and software. The system can realize scanning the ultrasound field, and obtain the characteristics parameters. Finally, the achieved target is introduced. The range of frequency is from 0.5 MHz to 60 MHz with 10 MPa@1 MHz peak-to-peak sound pressure value. The scanning configuration has the spatial accuracy better than 0.02 mm, and X/Y/Z scope larger than 400 mm. The above parameters mainly meet the requirement of the therapeutic sound field.

The basic theory of the spatial light modulator and the algorithm based on space-time adaptive system is discussed deeply which used to the core of the photoelectric system configuration by which key components applied to solve the control function. This paper discusses the hardware system. Usually, an SLM modulates the intensity of the light beam. However, it is also possible to produce devices that modulate the phase of the beam or both the intensity and the phase simultaneously. Besides, the discuss includes the control on the SLM for spatial information of the amplitude, phase, frequency, polarization, and the intensity of energy research. A typical model is used to illustrate the feasibility, and the criteria is developed.

The effects of monochromatic light modes and filtering systems on the measurement of spectral responsivity of photovoltaic(PV) modules are analyzed. According to the structure characteristics of PV modules, a PV module spectral responsivity measurement device was established based on the steady-state monochrome light source, main bias light source, auxiliary bias light source and phase-locked filter testing system. The nondestructive testing of spectral responsivity of solar cells in PV module was realized. The effects of irradiance of main bias light source, irradiance of auxiliary bias light source and temperature of PV module on spectral responsivity and spectral mismatch factor are analyzed. The influence of different sampling monochrome spot area on the relative spectral response measurement of solar cells under small spot test conditions is analyzed. The spectral responsivity of the PV module slices was tested by using the small spot measurement system. The accuracy of the nondestructive measurement device is verified by comparing the nondestructive test results with the slice measurement results.

GaInP₂/InGaAs/Ge triple-junction solar cells have become the main energy source for space on-orbit applications. For the sake of the three composed sub-cells, including GaInP2, InGaAs and Ge sub-cell, the monolithic triple-junction solar cells can make use of solar irradiance in the wavelength range of 300 nm to 1800 nm. Before assembled into space solar arrays, each solar cell’s current-voltage curves should be measured in laboratories on earth by AM0 solar simulators, to know their key parameters especially short circuit current. Solar cell’s current-matching is crucial for assembling into arrays. While spectral responsivity is essential for spectral mismatch factors (MMFs) calculation during the current-voltage measurement. MMF corresponding to each sub-cell should be analyzed, so spectral responsivity of each sub-cell of monolithic solar cell was required to be measured out. But sub-cells are connected in series in a monolithic multijunction solar cell, and current-limiting effect makes traditional spectral responsivity measurement which is suitable for single-junction solar cells not applicable anymore. For measuring the spectral responsivity of monolithic multi-junction solar cells, optimized bias light and bias voltage are required to make the tested target sub-cell be the current-limiting one. The wavelength range and irradiance intensity of the bias light, the direction and value of the bias voltage, should be chose and adjusted appropriately during the measurement, otherwise will lead to measurement artifacts and obtain incorrect results. In this paper, combing optimization of bias light and bias voltage with monochromatic light system, we would present method and detailed procedures for measuring the spectral responsivity of monolithic GaInP₂/InGaAs/Ge triple-junction space solar cells.

Nowadays, Light Emitting Diode (LED) and related products are popular in everyday lighting. Especially colour LEDs are widely used in colour application such as outdoor display, traffic signal light and cars. Precise photometric measurement results for those LED products are necessary due to needs of the international or domestic commercial trade. In the testing lab, people usually use photometer and related photometry equipment to measure LEDs. The photometer mimics the human eyes however it is not exactly the same. Thus, colour correction factor (CCF) is applied when the relative spectral response of the photometer S*(λ) is different from the photopic luminous efficiency function V(λ). Since the CCF is the most significant uncertainty component in LED total luminous flux and averaged LED luminous intensity measurement, the evaluation of uncertainty of CCF become more important in National Institute of Metrology China (NIM). Recently the Monte-Carlo method, as known as numerical simulation technique, is utilized to evaluate uncertainty by generating millions of random variable with related distribution function. The input mathematical model of the photometer S*(λ) and spectra of measurand PLED(λ) are described. The propagation of the uncertainty is also introduced. Examples of the evaluation of CCF uncertainty are shown.

In order to improve the real-time and portability of the moving target detection and tracking (MTDT) system, a compact FPGA-based MTDT system is built in this paper by using the parallel computing and flexible programming of Field Programmable Gate Array (FPGA). In order to realize the detection and tracking of moving targets on resource -constrained FPGA, some MTDT algorithms is analyzed firstly, and appropriate modifications were made without changing the basic principles to make it adapt to the limited logical resources of the Xilinx Spartan -6 series of FPGA chip selected in this design. Then the FPGA system is composed of four units: the image acquisition unit, the image storage unit, the image pre-and post- processing unit and the image display unit. Two image difference methods, an inter-frame and a background difference method, are implemented in the system. Finally, the moving target can be directly indicated on a video graphics array (VGA) displayer in the image display unit. The test results show that the system can detect and track a single target in real time in various resolutions at various frame rates, i.e. VGA @30fps and 15fps, 720p @15fps.

Accurate forecast of solar irradiance is significant for related domains. Because accurate forecasts can help relevant researchers plan the management and application of solar energy that can be used in nuclear power stations and power plant. In this paper, an approach of solar irradiance forecasting based on artificial neural network (ANN) is adopted. The dataset from April 1st, 2017 to May 31st, 2018 was measured by the meteorological station in Yunnan Normal University. Multilayer perceptron model (MLP) and the variables, such as daily solar irradiance, air humidity, and relevant time parameter are employed to forecast solar irradiance in future 24 h. Moreover, the method of cross-validation is used to guarantee the robustness of experimental results. The results show the normalized root means square error (nRMSE) between the measured data and forecasted data is about 1.8~20.07% (1.8~10.6% for the sunny day, 11.6~20.07% for the cloudy day). Compared with ANN model, the nRMSE on the model of K-Nearest Neighbor (KNN), Linear Regression (LR), Ridge Regression (RR), Lasso Regression, Auto-Regressive and Moving Average (ARMA) and Decision Tree Regression (DTR), are 35%, 31%, 30%, 26%, 23% and 11% (unstable) respectively. It means that the performance of our model satisfies related applications.

Lucky imaging technology is a post-processing technique for eliminating the influence of atmospheric turbulence in astronomical images to obtain high-resolution images. Reconstruction usually realized by using a desktop computer system. However, this post-processing method based on CPU can’t meet the real-time requirements of some astronomical observers. Based on a prototype of a FPGA-based lucky imaging system developed with our laboratory, a technical solution of lucky imaging technology based on Gigabit Ethernet is presented in this paper. The original short exposure images can input into the FPGA-based lucky imaging system via a Gigabit Ethernet interface. Some functional modules related to data transmission through Gigabit Ethernet are designed, and the lucky imaging processing and VGA display modules in the prototype system are transplanted. After all these works, a new lucky imaging processing system which is based on Gigabit Ethernet, has been built. This paper will firstly introduce the design methods and the implementation techniques of the Ethernet receiving module, FIFO module, DDR3 module, and the transplantation methods for the s election module, registration module, superposition module, and display module. The observed short exposure images are sent to the FPGA system by an image workstation via Gigabit Ethernet. The software in the workstation is developed in C#. The programming method is also introduced in this paper. Experiments show that compared with the old prototype system, the total time for processing 1,000 short exposure images is reduced from 42 seconds to about 10 seconds, and the real-time performance of the new system is improved.