PTB is currently developing and setting up a new form measurement system for large optical surfaces with diameters up to 1.5 m. One objective is to measure flat surfaces with standard uncertainties of a few ten nanometers. Another objective is the form measurement of slightly curved specimens with a radius of curvature of 10 m or more with standard uncertainties below 1 μm. The new system will measure the specimen's topography in subapertures. Information is needed about the position and angle of each subaperture, so that the measurement errors of individual subapertures measurements do not lead to larger errors in the complete topography. For the measurement of slightly curved specimens, a highly accurate measurement of the rotations of the measuring head within a measuring range of ±5° is required. For this purpose, an angle measuring system for the measurement of the roll, pitch and yaw angle with an interference-based illumination is being developed at PTB.

In the traditional fringe projection technique, the speed of projecting 8-bit sinusoidal fringe patterns is slow. To address this issue, this paper designs a novel high-speed MEMS projector by using its high-frequency resonant and forward-reverse scanning. In high-speed projection mode, light sources may be unstable and produce more light-intensity noise. To reduce the standard deviation of phase errors, this paper proposes a method of generating high-quality sinusoidal fringe patterns. The proposed method encodes the traditional fringe pattern into the phase of the sinusoidal fringe pattern. Therefore, from a mathematical expression perspective, the actual projection pattern is a composition of two sine functions. The proposed method uses multiple projected patterns to computationally generate a high-quality phase-shifting pattern. Subsequently, the high-accuracy phase can be solved by using a phase-shifting method to process these generated high-quality phase-shifting patterns. Finally, the experimental results demonstrate the feasibility of the self-developed MEMS projector and the robust noise resistance of the proposed method. Compared to the traditional phase-shifting method, the proposed method can significantly improve phase accuracy in the case of the same required number of images.

Three-dimensional reconstruction technology based on fringe projection profilometry is widely used in industrial measurement, defect detection, and other fields. The lateral and longitudinal resolution of 3D reconstruction is mainly determined by the camera's resolution, while the axial resolution along the z-axis is primarily determined by the accuracy of phase retrieval. In industrial component inspection, the 3D measurement system's ability to distinguish the small height differences is crucial. In this paper, we propose a method to evaluate the system's axial resolution based on plane fitting. Firstly, the proposed method employs a multi-frequency 12-step phase-shifting method to generate the point cloud of a step-like standard part. Then, we generate an image mask by setting the threshold of the modulation intensity to filter out abnormal point clouds. To address the multi-plane extraction problem, we propose a multi-plane fitting method based on the RANSAC framework. This method constructs a model score using orthogonal distances and sequentially extracts planes from the point cloud using the least squares method. Finally, our method determines the system's axial resolution by calculating the distances between planes. Given the importance of axial resolution in industrial inspection, our proposed method has significant practical application value for any given structured light system.

The three-frequency heterodyne phase shift profilometry is widely used in high-precision 3D reconstruction. However, the high accuracy comes at the cost of requiring many projected frames, which increases measurement time and decreases measurement efficiency. To address this challenge, we propose a rapid, high-precision absolute phase acquisition method called X+1+1, which fully integrates the accuracy advantages of the multi-frequency n-step heterodyne phase-shifting method and the speed advantages of the Modified Fourier transform profilometry (MFTP). The highest frequency gratings use the standard X-step phase-shifting method to determine the wrapped phase, ensuring high unwrapping accuracy and obtaining background light intensity. For intermediate and low frequencies, a single-frame grating and the Backgroundgenerated Modified Fourier transform profilometry (BGMFTP) are used to solve each wrapped phase to reduce the measurement time. Finally, the heterodyne method processes these three-frequency wrapped phases to obtain the absolute phase. Experimental results demonstrated the high accuracy and speed of this method in the 3D measurement process. Compared to traditional Fourier transform profilometry, the X+1+1 method has a 53% improvement in accuracy, while maintains the same level of performance as the three-frequency four-step heterodyne method in continuous non-marginal flat areas and the projection time was reduced by approximately 50%. The proposed X+1+1 method provides a new solution for balancing speed and accuracy in the application and promotion of structured-light 3D measurement.

Heterodyne grating interferometry plays a crucial role in various high-precision applications due to its superior performance across multiple fields. However, achieving picometer-level accuracy is hindered by multiple error sources. One of the critical challenges stems from optical component ghost reflections, which introduce significant measurement inaccuracies. Despite their impact, the error modeling of ghost reflections is complex, and current high-precision real-time error suppression algorithms are lacking. To address this, we establish an accurate error model for ghost reflections in the classical configuration of grating interferometers, focusing on phase and displacement calculation errors. Furthermore, we develop a real-time ghost reflection filtering algorithm based on the Kalman filter, which reduces the error by over 90% while maintaining real-time performance. In summary, the proposed ghost reflection modeling and error elimination methods significantly enhance the potential of heterodyne grating interferometers in achieving picometer-level precision.

The positions of the traditional three-position spherical absolute measurement are the cat's eye position, the confocal position, and the confocal position rotated 180°. Rotational operation can introduce misalignment errors that affect the measurement results. In this paper, it is shown that only two measurements of cat's eye position and confocal position are necessary to obtain the absolute surface of the measured sphere through Zernike polynomial fitting. When solving the three-position spherical absolute measurement with Zernike polynomials, the number of unknowns is greater than the number of equations, resulting in the inability to solve. By analyzing the equation, the relationship between the Zernike coefficients before and after rotation can be found, resulting in a solvable system of equations.

In the current field of phase measuring deflectometry (PMD) techniques, the primary factor affecting the low-order shape errors of the measured specular surface originates from the uncertainty in geometric calibration. To address this issue, this paper presents a full simulation pipeline of PMD using the ray tracing technology within the Python framework. It integrates phase analysis and gradient-surface reconstruction algorithms based on preset surface types to analyze the error impact on the final retrieved profile, with the help of Zernike coefficients characterization. To further analyze the potential error influences of the PMD system in actual physical scenarios, a comprehensive ray tracing modeling simulation was conducted, considering system noises, nonlinear effects of the imaging subsystem, geometric calibration errors and the impact of displayer surface deformation. This simulation starts from forward ray tracing to construct the model of fringe signal propagation and combined it with reverse ray tracing to solve for the surface shape of the measured specular surface. It further clarifies that under the hybrid influence of comprehensive error sources, the primary contributing factors to the surface shape residuals of the measured mirror are low-order shape errors and certain high-order shape errors such as astigmatism and coma aberrations.

Nowadays, color-coded patterns are widely used to make real-time 3D shape measurement possible based on fringe projection profilometry (FPP). However, color crosstalk between the color camera remains a primary limitation of this method. In order to reduce the influence of color crosstalk on the phase retrieval accuracy, an accurate color crosstalk coefficient calibration method is proposed for color decoupling in this work. Firstly, based on the orthogonal fringe projection mode, the influence of color crosstalk coefficients on wrapped phase error is theoretically derived. Meanwhile, the truth phase values are generated based on smooth surface polynomial fitting to eliminate phase artifacts. Finally, by projecting the designed color orthogonal fringe patterns onto a standard plate, separate images from R, G and B channel could be obtained to extract the phase error, which can be further used for color channel crosstalk coefficients calibration. Multiple experiments with a standard white plate and sphere have verified that the method effectively improves phase quality, making it suitable for fast and accurate 3D shape measurement.

In the process of water turbidity detection, in order to eliminate the significant influence of water temperature on turbidity measurement values, this study investigates a temperature compensation algorithm. By utilizing the GaAIAs infrared scattering principle, a water turbidity sensor was designed. The working principle is based on optical scattering theory. It utilizes a 880nm GaAIAs IRED semiconductor light-emitting element to emit light sources. By detecting the intensity of scattered light generated when the infrared emission tube's light shines on suspended particles in water, the sensor achieves measurement of water turbidity values. After introducing the temperature compensation algorithm for fitting processing of data, the error range of the turbidity sensor data is greatly reduced, which significantly improves its accuracy performance. Besides the interference caused by bubbles, the turbidity sensor based on GaAIAs IRED has been optimized for comparison values in the Formazin standard solution. This enables the sensor to effectively offset the influence of temperature changes on measurement results, demonstrating higher resistance to temperature interference.

The accuracy of the absolute position and orientation of sub-mirrors in large-aperture optical systems significantly impacts system performance. The precision of sub-mirror alignment directly affects the surface shape error of the main mirror, which, in turn, affects imaging quality and overall system performance. Two main methods for position and orientation measurement are electromagnetic displacement measurement and optical displacement measurement. While electromagnetic methods achieve high precision, their complex structures and susceptibility to environmental factors pose challenges. Optical displacement measurement using grating encoders, which rely on grating pitch as a reference, offers high stability and broad applicability.

To address sub-mirror alignment accuracy in large-aperture telescopes, we propose an absolute six-degree-of-freedom grating encoder based on spot position monitoring. This encoder achieves four degrees of freedom (θX, θY, θZ, Z) absolute position and orientation detection using gratings. Additionally, we employ right-angle prisms for absolute position and orientation detection in the X and Y directions, enabling six-degree-of-freedom absolute position and orientation monitoring for sub-mirrors. The monitoring results serve as feedback for sub-mirror pose correction. To mitigate the impact of grating motion on X and Y displacement calculations, we introduce a displacement calculation algorithm based on ray tracing for error compensation, enhancing the accuracy of X and Y displacement calculations and achieving high-precision six-degree-of-freedom measurement and computation.

The multi-frequency hierarchical method is a well-established temporal phase unwrapping technique known for its high precision. However, its requirement for numerous images significantly reduces the speed of 3D reconstruction. To address this limitation, we propose a novel coarse-fine combined phase unwrapping method. This method reallocates the actual phase order into sequentially arranged coarse and fine orders. The coarse order provides the primary range for the actual phase, while the fine orders precisely locate it. The proposed method requires only six images to achieve high-frequency absolute phase. Experimental results demonstrate that, compared to the popular three-frequency three-step phase-shifting method, the proposed method reduces the number of projection patterns by three while maintaining similar accuracy. Therefore, this method holds significant potential for high-speed 3D reconstruction applications.

Autocollimator is a common device for non-contact measurement of the angular position of objects in space. Its accuracy can vary from a few arc seconds to a hundredth of an arc second, and the more accurate the device, the more factors must be taken into account during measurements. At the moment, there is already a significant body of research on the factors that affect angular measurements using an autocollimator. These include the size, reflectivity, and flatness of the reflecting surface; the distance between the surface and the autocollimator; the presence and configuration of any aperture in the beam path of the autocollimator; and many other factors. Typically, the object of these studies is a high-precision autocollimator (with accuracy greater than 0.1 arc seconds), and the contribution of studied parameters is usually less than 1-2 tenths of an arc second.

In the process of using a less accurate digital autocollimator (with a claimed accuracy of 0.25 arc seconds), the authors also encountered the influence of various parameters in the measurement setup, but of a greater value. This led to additional research.

This paper presents an experimental analysis of the complex effects of the distance to the reflecting surface and its size, as well as the impact of non-flatness on the surface. The random errors of the autocollimator in different operating modes are also analyzed.

Two-dimensional galvanometer scanners are critical instruments in optical scanning systems. However, the scanning trajectories of galvanometer scanners are susceptible to distortions caused by mechanical and electrical imperfections, which inevitably compromise optical scanning performance. While closed-loop feedback signals can help mitigate these distortions, their accuracy is often restricted by perturbation during prolonged high-speed operation. In this study, we propose a deep learning-based trajectory correction method to achieve high-performance optical scanning in galvanometer scanners. By integrating a Convolutional Neural Network (CNN) with a Long Short-Term Memory (LSTM), the hybrid architecture effectively reduced trajectory errors by over 97% across three driving configurations. Furthermore, the optical performance was assessed by imaging three different patterns using the corrected trajectories, revealing a substantial improvement in image quality compared to those reconstructed from the original uncorrected trajectories.

Micron-level surface damages can seriously affect the optical and mechanical properties of large-aperture optics, so it is of great significance to perform high-precision inspection and mitigation of surface damages. Surface micro-damages are not only multi-category but also randomly distributed on the optics. Manual inspection and mitigation are not only time-consuming but also difficult to ensure the accuracy and reliability of mitigation, so it cannot meet the engineering requirements for large-volume mitigation of optics. In order to solve this problem, an intelligent inspection system framework for optics surface damage mitigation is proposed in this paper. The inspection system consists of an optics surface ranging fitting module, a dark-field rapid inspection module, and a multi-illumination micro-inspection module. Based on the above modules, a damage inspection process flow is established, including automatic alignment of optics surface, rapid dark-field inspection of flaws with large field of view, microscopic precision inspection of damages with small field of view, automatic configuration and execution of damage mitigation strategies, and quality control of mitigation structure. In order to realize the above flow, a predictive model library related to damage inspection is constructed, including: a dark field classification and size calibration model, a microscopy multi-classification model, and a mitigation quality inspection model. The automation and intelligence of the process flow is achieved by replacing the manual decision-making process with predictions from the model library. Based on the proposed framework, the working principle and workflow of the damage intelligent inspection system are explained, and the inspection efficiency and automation level of the system are evaluated in this paper. The intelligent inspection system framework proposed in this paper can provide technical support for future high-volume mitigation of large-aperture optics.

The six degree-of-freedom (DOF) measurement is of significant importance in precision engineering and scientific research, especially in fields such as aerospace, manufacturing, and robotics. Among various measurement techniques, heterodyne grating interferometry stands out due to its high precision, strong anti-interference capabilities, and ease of multi DOF expansion. However, existing methods have some issues: firstly, polarization and frequency aliasing can lead to high periodic non-linear errors, affecting measurement accuracy. Secondly, it is difficult to achieve six DOF measurement while ensuring miniaturization and high precision. To address these issues, we presents a heterodyne-based six DOF measurement grating interferometer, achieving sub-nanometer precision. By employing a heterodyne (dual-frequency) grating interferometry technique, the measurement accuracy is significantly enhanced. The system offers comprehensive spatial measurement capabilities, with 3-DOF displacement measured using interference signals from two-dimensional gratings and 3-DOF angular measurements derived from spot displacement on a quadrant photodetector. To address error reduction, a quasi-common optical path design minimizes polarization/frequency mixing-induced nonlinear periodic errors and optical dead zone effects, reducing measurement error to sub-nanometer levels. Additionally, a compact system design is realized. These innovations enhance the performance and applicability of precision measurement technologies, offering strong support for advancements in the field. Overall, the proposed system achieves sub-nanometer precision, 6-DOF measurement, low error levels, and compact design.

We present an analysis of the advantages and disadvantages of recording and monitoring of nonlinear strain waves in a solid waveguide made of a nonlinearly elastic material (polystyrene) using three techniques: off-axis digital holography with observation ‘in-transmission’ and ‘in-reflection’ and acoustical diagnostics utilizing piezoelectric transducers. Holographic ‘in-transmission’ recording was shown to provide more reliable determination of wave parameters owing to both higher resolution and sensitivity to longitudinal waves only. When monitoring the wave process by piezoelectric sensors attached to the lateral surface of the waveguide, the sensor sensitivity to shear waves did not allow us to isolate the contribution of longitudinal waves in a prolonged input part of the waveguide.

In this work, we present the general method to estimate the measurement uncertainty related to opto-electronic and photonic systems. It consists in a modern method, which follows the recommendations of the Guide to the Expression of Uncertainty in Measurement. After determining the uncertainty propagation equation, we review the elementary uncertainty terms separated into two distinct categories. First of all, statistical terms are studied. Then, the other elementary uncertainty terms such as those linked to the connection to international standards or manufacturer data, as well as the elementary terms linked to variations in environmental parameters such as temperature, acceleration, or hygrometry, or those linked to quantities studied such as the wavelength of lasers or that linked to the misalignment of the beam in space. We illustrate this method with two examples, an optoelectronic oscillator and that of a Brillouin Light Scattering measurement system.

To solve the testing problem of ring surface, a non-splicing interference testing system is designed by combining digital phase measurement technology. Using closed-loop circuit feedback control to realize the precise control of PZT for small displacement, while collecting the N frame sequence interference light intensity map In (x,y). In order to reduce the adjustment error introduced by manual adjustment, the error correction matrix is derived based on the misalignment error model under the cylindrical coordinate system. It has been proved that the testing system can realize high precision detection of 360° rotary cylindrical surface, and a high precision Talyrond565LT cylindrical degree instrument is used to measure the same sample for comparison validation. The experimental results show that the ring surface detection system studied in this paper can realize one-time and high-precision detection of the inner surface of 360° cylinder, and the measurement accuracy PV is better than 0.4λ(0.25μm)and RMS is better than 0.2λ(0.12μm).

The simulated grating for absolute measuring the transfer function of large-aperture Fizeau interferometer is proposed, combining with the surface and homogeneity absolute measurement data, the simulated grating absolute surface data without aberration can be obtained more accurately to achieve the full aperture transfer function absolute measurement at all spatial frequency. A 300mm aperture Fizeau interferometer experimental results show that the absolute surface errors of the three flats are less than λ/20(PV) and λ/100(RMS), and the homogeneity measurement is better than 1*10^-6. The optimized transfer function is better than 0.86 at 1 mm^-1 spatial frequency, which is a 10% improvement.

Large rectangular plane mirrors are widely used in high-power laser systems and synchrotron radiation sources, their surface precision affecting optical system performance. High-precision measurement methods are required to match these mirrors. The oblique incidence absolute measurement technique based on the rotational averaging method is a commonly method for these mirrors. But this method is complex, requires two additional plane mirrors. And it is limited by the angle of incidence, making it impossible to achieve both large aperture and high-resolution measurement simultaneously. Moreover, the method requires disassembling the test mirror during measurement, which significantly complicates the setup and adjustment process. Addressing the aforementioned shortcomings, this paper presents a high-precision measurement method for large rectangular plane mirrors. This method combines subaperture stitching techniques with the absolute measurement approach using the double shear translation method. It divides the test mirror into multiple overlapping subapertures and applies the double shear translation method to conduct absolute measurement on each subaperture region sequentially. Subsequently, employs algorithm to stitch the results together to achieve a complete surface. This method balances large aperture and high-resolution measurement, eliminates the influence of the reference surface. During the measurement process, only translations of the test mirror are required, making setup and adjustment relatively straightforward. Experimental validation of this method has demonstrated its ability to achieve high-precision measurement of rectangular plane mirrors. This paper presents an effective approach for high-precision measurement of large rectangular plane mirrors.

We proposed an absolute distance measurement method with a large non-ambiguity range based on a polarization-multiplexed dual-comb fiber laser. By fully exploiting the intracavity linear loss based gain profile tilting and residual birefringence, polarization-multiplexed dual-comb pulses with tunable repetition rate difference and overlapping spectra in the 1530-nm gain region are obtained. The repetition frequency difference could be continuously tuned from ~89 to ~194 Hz. The alternative sampling under different repetition rate difference is experimentally verified to be effective approach to extend the non-ambiguity range in the single-cavity dual-comb ranging. The non-ambiguity range could reach thousands of kilometer while the precision could reach at least on the order of hundreds of micrometers. These results indicate a simple and intriguing route with a free-running laser source to obtain ranging with large non-ambiguity range, showing high potential in the applications such as satellite formation flying, large-scale 3D surface morphology measurement and so on.

The use of aspherical and freeform optics is increasingly prevalent to overcome aberrations and facilitate compact optical systems. However, achieving simultaneously fast, flexible, and accurate measurements of such surfaces remains a challenge. Multiple Aperture Shear-Interferometry (MArS) utilizes multi-spot illumination to measure a wide spectrum of such surfaces without adjusting the measurement system. Using the wave vectors of wave fields reflected by the surface as well as the positions of the individual light sources, the surface form is reconstructed using an inverse ray-tracing approach. Hence, the accuracy of the measurement directly depends on knowledge of these entities. In this publication we present a calibration approach for wave vectors incident across the measurement plane. Secondly, we introduce a geometric and spectral calibration method for the multi-spot illumination, ensuring accurate and consistent measurements across diverse surfaces.

A dispersive Fourier transformation-based ranging method utilizing a femtosecond laser frequency comb is demonstrated. The target and measurement signals interfere through a Mach-Zehnder interferometer and then enter a single-mode fiber with a sufficiently large group velocity dispersion (GVD) to be stretched and extended. The spectral interference information is mapped to the time-domain waveform. The time-frequency conversion function, obtained through calibration, converts the time-domain data into the frequency-domain data. After applying a Fourier transform, the measured distance is determined using the peak-interval method. In multiple measurements with an interval of 200 μm, the average error is within tens of microns., which can be further reduced with a higher-precision displacement table.

This paper presents a study on the spot location method and system based on QPDs. We construct a mathematical model of the relationship between spot position variations and detector responses, systematically analyzing the impact of the spot size and detector parameters on spot location accuracy. We propose an ultra-precision Gaussian spot location algorithm based on QPDs, along with a common-path laser light source fluctuation error compensation structure and method, and validated the method through simulation experiments. The experimental results show that this scheme can achieve submicron level spot positioning accuracy. In the measurement range of 1 mm, the measurement error after compensation is reduced by 97% compared to before compensation. Additionally, the repeatability and stability demonstrate excellent performance. This study provides a laser light source fluctuation error compensation method and an ultra-precision Gaussian spot location algorithm based on QPDs for laser measurement technology, significantly improving measurement accuracy and environmental interference resistance.

Large-area gratings play a critical role in various fields such as astronomical observations, laser fusion, and precision measurements, with an increasingly urgent demand for the fabrication of meter-scale gratings. Interference lithography (IL) offers the capability to produce high-quality gratings and holds significant potential for scaling up grating sizes. The stability of the exposure light field significantly affects the processing quality. Therefore, this paper proposes a fringe locking technique based on multiple reference gratings.

In the dual-beam interference lithography setup with large-aperture optics, a reference grating is used to monitor the exposure field. The reference fringes are recorded by a CCD camera, and the drift values are calculated using a cross-correlation method. These values are used to generate the control signals, which actuate the motion mechanisms to dynamically adjust the phase and period of interference field. However, relying on a single reference grating is insufficient to capture the conditions across the entire exposure field.

Therefore, we conducted an analysis of the errors across the entire exposure field and identified period error as the primary cause of this phenomenon. To address this, fringe patterns from two reference gratings are used to monitor periodic variations in the interference field. The feedback calculated by these variations is used to adjust the motion mechanism. altering the angle between the two beams to achieve periodic compensation. Experimental results show that after implementing periodic compensation, the fluctuation RMS of the interference fringes decreased from 0.24λ to 0.06λ, demonstrating significant improvement.

In modern intelligent living, X-ray computed tomography (CT) exhibit the great potential in industry for non-destructive dimensional quality control purposes, which serving a range of monitoring and management, from chips, integrated circuits, batteries, and automotive components. In this paper, a special standard sample was designed and manufactured to test critical dimensional characteristics on different CT systems. Additionally, a sequential participation scheme, together with detailed measurement procedures and reporting instructions, has been proposed to evaluate measurement uncertainty and determine metrological performances of CT systems. Finally, a series of experimental tests were carried out to demonstrate dimensional measurement errors of CT systems. Those results have been proven to be amenable for practical purposes through many tests so that it might be applicable to achieve accuracy and traceability issues of CT systems in industrial intelligent production line.

Photometric stereo reconstructs surface shape with intricate details by analyzing the light propagation process and has attracted wide range of applications such as industrial measurement. However, the presence of non-Lambertian reflections on real-world scenarios poses a significant challenge to surface normal estimation methods. Most of the existing approaches aim to achieve reasonably accurate results by filtering non-Lambertian observations through employing iterative frameworks. Based on these, this study introduces a novel surface normal estimation method that formulates the observation selection and regularization as a smooth L₁ regression problem. Specifically, we sort pixels by intensities and select effective observations through a threshold strategy, the surface normal are then estimated by a smooth L₁ loss function to resist non-Lambertian corrosions so that facilitate a more accurate result. The performance of the method is validated through testing on real-world datasets, with an impressive average angular error as low as 11.92°. In experiments, surface reconstruction of a turbine blade is successfully achieved, showcasing its applicability in industrial manufacturing.

This study examines the optical performance of three fisheye lenses under various polarization states, focusing on polarization aberration. Using ZEMAX software for simulation and a controlled laboratory setup for measurements, we use the MTF to analyze imaging quality. Results show that polarization significantly affects imaging, particularly at the edges, where polarization aberration causes increased distortion.

Large diffraction gratings have been widely applied in fields from industrial measurement to modern scientific facilities. The scale and geometrical accuracy of a grating directly affect its operating performance. Optical mosaic grating fabrication, which produces a large diffraction grating by multi-exposing different areas of a substrate, has shown great advantages in terms of simplicity and productivity over other methods. However, groove shape defects resulted from disturbance of interference fringes and mosaic seams resulted from misalignment of exposure patterns compromise the quality of the produced gratings and impede this method from expanding to larger scales. As a result, active fringe locking and alignment control must be performed during and between each exposing process.

This paper proposes a fringe locking system consisting of Moiré pattern monitoring via a CCD camera and closed-loop piezoelectric-driven mirror control. To ensure the geometric consistency of the fabricated gratings and the effectiveness of the fringe locking system, an alignment method based on morphological operations and Fast Fourier Transform (FFT) analysis of the image is introduced. Experiments show the proposed system operates at 250 Hz, with significant suppression of low-frequency disturbance components below 100 Hz. The Root-Mean-Square (RMS) value of phase drifts remains below 0.02 fringe periods during the 60-second exposure, laying the foundation for fabricating large optical mosaic gratings.

Head-mounted displays (HMDs) require precise measurement of virtual image distance for user comfort, but this is challenging due to dynamic variations. This paper addresses the difficulty by proposing a prototype using a variable-focus liquid lens and a calculation model for virtual image distance. We developed an experimental platform to validate the method and introduced an optimization algorithm to find the optimal focal length for maximum sharpness. Results showed a distance error of about 5 cm, confirming that our method accurately measures virtual image distance in HMDs, with potential applications in virtual and augmented reality.

This work aims to simplify and optimize the data processing of laser triangulation ranging method by utilizing deep learning for intelligent measurements, leading to enhanced measurement accuracy. Firstly, a nonlinear programming genetic algorithm with elitist strategy (E-NPGA) is employed to determine the optimal optical system parameters, resulting in the development of a laser triangulation ranging system. A deep neural network is then established for distance evaluation. Experimental results demonstrate that the deep learning based method proposed in this work enables a distance measurement with a root mean squared error within the range of 0.8 to 1 μm and a mean absolute error of below 0.7 μm, which offers a feasible intelligent measurement approach.

In this work, a solution based on sub-sampling technology for heterodyne signals is proposed. While achieving higher measurement resolution and measurement speed, the performance requirements for the analog-to-digital converter and microprocessor are greatly reduced. The heterodyne signal is a sparse signal with a single frequency at each moment, only its phase offset contains displacement information. We use the pulse counting method to obtain the periods of the signal, and a sampler with a sampling rate well below the frequency of the heterodyne signal. The phase of the sampling point can be restored through sub-sampling technology and extended Kalman filtering. In the experiment, we used 16-bit ADCs with a 600 Ksas sampling rate to sample the heterodyne signals with a center frequency of 10 MHz and the dynamic range from 1 MHz to 19 MHz. The simulation results indicate that our method can effectively calculate the phase information of the interference signal.

The grating interferometer, with its advantages of high resolution, low cost, and robustness in various environmental conditions, plays an irreplaceable role in the field of ultra-precision measurement. However, the existing Z-axis measurement methods have relatively low resolution, which limits their precision to atomic levels. In order to further improve the accuracy of the heterodyne grating interferometer, this paper proposes an improved optical path for increasing the optical subdivision number in the Z direction. By utilizing a combination of beam splitters and polarizing beam splitters, the Z direction achieves quadruple optical subdivision, enabling sub-nanometer level measurements. Experimental verification demonstrates that this approach can achieve a Z-direction resolution better than 0.2nm, with a 50nm travel repeatable accuracy of 0.5nm, a 50nm step size linear accuracy of 0.04%, and a system stability of 4nm within 5 minutes. The periodic nonlinear error is better than 1nm. In addition, The proposed improved optical path in the Z direction can be further extended to a three-degree-of-freedom measurement system, making it more compact and suitable for achieving sub-nanometer level measurements. This method has the advantages of simple installation, high precision, and stability. It holds significant practical value in industrial production, and can be applied in precision mechanical manufacturing, scanning beam interferometric lithography, and other ultraprecision positioning applications.

Studies of matrix angle meters with a scale diameter of 5 and 23 mm have been carried out. The objective of the research was to assess the possibility of achieving the predicted meteorological parameters at the level of hundredths of an arc second for angle measurements and several nanometers for linear. To do this, work was carried out to stabilize the meters using a heat sink and thermal protection. Angular measurements were carried out on the basis of a goniometer rotary platform with an angle sensor LIR. Linear measurements were carried out on a two-channel stand with two identical matrix displacement meters. In both experiments, 1.3 Megapixel CMOS digital cameras were used as an image analyzer. It is concluded that the random error of the studied matrix meters does not exceed 0.05 arc-sec for angular measurements and 15 nm for measuring displacements.

Single-frame high-precision 3D measurement using deep learning has been widely studied for its minimal measurement time. However, the long physical and semantic distances make the end-to-end absolute phase reconstruction of single-frame grating challenging. To tackle this difficulty, we propose the DSAS-S2AP-X (Dual-Stage Auxiliary Supervision Network for Single-Frame to Absolute Phase Prediction with X) strategy, which includes the secondary highest frequency unwrapped phase and the highest frequency wrapped phase supervision branches. It combines a multi-frequency temporal phase unwrapping model with existing regression networks X (meaning arbitrary). Experimental results have shown that the DSAS-S2AP-ResUNet34 strategy can reduce the mean absolute error (MAE) and root mean square error (RMSE) of the absolute phase by 34.3% and 25.9% respectively based on the ResUNet34.

At present, a majority of virtual reality (VR) technologies on the market employ static distortion correction by predistorting the virtual image. However, this compensation method is only effective when the pupil remains in a fixed position for virtual display device. When the pupil moves within the eye box of the VR device, the virtual image may deviate from the target position, rendering the compensation ineffective. Due to the optical asymmetry of the lens, different distortions can be perceived by the human eye as the pupil moves, which adversely affects the user's visual experience. Therefore, it is essential to measure and evaluate dynamic distortion for adjusting pre-compensation parameters according to the pupil's position, as well as for further optimizing optical systems with low dynamic distortion. In this paper, we analyzed the cause of dynamic distortion in virtual reality and proposed a novel method for characterizing dynamic distortion, allowing for quantitative analysis of dynamic distortion compared to traditional optical flow maps. A prototype was fabricated for dynamic distortion evaluation, and both simulation and measurement of the dynamic distortion were conducted. The results demonstrate a strong correlation between the simulations and measurements.

Phase-measuring deflectometry (PMD) is a crucial technology for measuring the forms of specular surfaces. However, existing stereo-PMD techniques have noticeable weaknesses when it comes to measuring structured specular surfaces. This limitation arises because the optical axis of the imaging system must intersect significantly with the optical axis of the display system, following the law of reflection. In contrast, near optical coaxial phase measuring deflectometry (NCPMD) offers several advantages over conventional PMD techniques. These advantages include a compact configuration, lightweight design, and minimal measurement errors due to the shadows of surface structures. NCPMD achieves this by utilizing a plate beamsplitter. With the assistance of the plate beamsplitter, the optical axis of the display screen can be configured much closer to the optical axis of the imaging system. As a result, the system becomes more compact and significantly reduces volume compared to the conventional PMD configuration. However, the introduction of the plate beamsplitter can impact on the measurement accuracy of the system. Specifically, the refractive effect of the beamsplitter can reduce the measurement accuracy. To address this challenge, a refraction error model is proposed for the NCPMD system. This model considers the influence of the plate beamsplitter’s refraction, allowing for the determination of measurement errors caused by this effect. Additionally, a virtual simulation system is established to analyze the shape reconstruction error resulting from the plate beamsplitter’s refraction. According to the experiments and results, the measurement accuracy can be effectively improved after the refractive error compensation.

High-accuracy mirror surface measurement using three scanning interferometric displacement sensors, with motion error calibrated, is proposed for X-ray mirror metrology. The motion error of the scanning displacement stage significantly affects the high-accuracy measurement of mirror surfaces during scanning. The influence of motion errors on surface height measurements is studied. After eliminating motion errors with a system comprising three scanning interferometric displacement sensors, the mirror surface can be obtained. The formula for the surface height solution is derived, and the residual error terms are analyzed. A method of error reduction using three reference mirrors to calibrate distance is proposed. The calibration and test experiments are conducted. Experimental results demonstrate the effectiveness of calibration, and the measurement repeatability is 7.39 nm.

A real-time online ranging system is proposed using the frequency domain peak interval measurement method. By utilizing an NPR-locked, all-fiber, wide-spectrum erbium-doped femtosecond laser, a gain distribution with a center wavelength of 1560nm is obtained, with a repetition frequency of up to 14.54MHz, and then a femtosecond laser source with a spectral width of 38nm at -3dB can be obtained by adjusting its polarization state, which can improve ranging accuracy. By a combination of an upper computer system an all-fiber Michelson interferometer, real-time capture and processing of spectral interference data can be achieved, thereby realizing real-time acquisition of relative displacement distance. Experimental results show that within the coherence length, the measurable relative distance is around 2cm, and the measurement accuracy can reach 5μm.

This paper preliminarily investigates the performance of machine vision system from the perspective of contrast and object detection process. We set up a testing system using a lightbox, transmissive/reflective test charts, a photometer, and two cameras. The photometer was used to obtain the standard luminance of the test chart. First, we obtain the DN response characteristics for luminance of two cameras with different dynamic ranges (72 dB and 123.6 dB). Based on this result the relationship between luminance domain and camera domain contrast ratio is provided. Distribution of the signal and contrast in the camera domain under low luminance conditions show the advantage of 16bit camera over 8bit camera. To link the camera's performance in practical scene, we conducted imaging tests of reflective resolution targets under various illuminance levels. We observed that the contrast and imaging quality of resolution targets by the camera at critical states can help establish correlation between single-metrics and scene-based imaging recognition performance evaluation.

The technical route of EUV light sources is divided into two routes. One is high power sources for high volume production, and the other is low for in-house metrology and performance studies on EUV-mask-blanks, EUV masks, and photoresists. This research focuses on the second technical route and concentrates on photoresist inspection. The current mainstream industrial applications include AIXUV’s EUV-LAMP, EUV-Tube from Phoenix EUV and Energetiq’s Electrodeless EQ-10 source. Our research is similar to AIXUV’s EUV-LAMP, which uses the Hollow Cathode cathode-triggered DPP-EUV source. Since the research is in its infancy, the achievement of various indicators of the light source is unidentified. To characterize the source’s in-band power (13.5nm 2% bandwidth), a power measurement based on a zirconium membrane filter, a Mo/Si multilayer mirror, and an EUV photodetector is proposed. At Xenon flow rate of 2.5 sccm, with pressure in the discharge chamber of few pascals, charge voltage of 3 kV, and a repetition frequency of 100 Hz, the 2%BW in-band power measured is above 5 W/4π sr.

In this paper, an approach for beam collimation by pupil segmentation is proposed. In this approach, the divergent or convergent wavefront of the beam to be collimated is divided into a series of subwavefronts by a microlens array, and the beam collimation is realized by comparing the difference of centroids between the actual spots and the reference ones under the paraxial approximation. In the experiment, the size of the beam to be collimated is limited by a stop aperture to satisfy the paraxial approximation. Using the proposed method, a divergent beam is collimated by a doublet with a focal length of 100 mm under the paraxial approximation. The test results of the collimated beam by a Shack-Hartmann sensor show that the root mean square of the wavefront of the collimated beam is 0.02 λ, having a good agreement with results of the proposed method. The experimental results show that the method is simple, low cost and highly accurate.

Currently, the incorporation of improved population initialization methods and strategies for adaptively adjusting crossover and mutation probabilities into genetic algorithms for mobile robot path planning has made some progress. However, certain issues still remain, such as poor quality of the initial population and improper setting of genetic algorithm parameters (e.g., crossover and mutation probabilities). These issues lead to slow algorithm convergence and difficulty in balancing multi-objective weights. To address these challenges, this paper proposes a path planning method that integrates the Ant Colony Algorithm with an improved Genetic Algorithm. The method first utilizes the Ant Colony Algorithm to plan multiple feasible paths, which are then used as the initial population for the Genetic Algorithm. Next, the fitness function considers path length, number of turning points, and travel time, and is used as the criterion for evaluating the optimal path. The multiple paths generated by the Ant Colony Algorithm are then ranked according to their fitness values, and a selected number of paths undergo adaptive crossover and mutation. Finally, a redundant point elimination strategy is employed to refine the paths, achieving obstacle avoidance and global path planning for the mobile robot. Simulation tests on a grid map demonstrate that, compared to traditional Genetic Algorithms, improved Genetic Algorithms, and other proposed improved algorithms, the method presented in this paper effectively shortens the path length and reduces the number of convergence iterations, showcasing advantages in both efficiency and stability.

Films are widely used in electronic shielding, surface protection, etc. Since the spectral reflectance of the thick film layer has enough peaks and troughs, there are various ways to extract its thickness, such as the extreme value method, the envelope method, the Fourier transform and so on. However, because the theoretical model of the extreme value method ignores the extinction coefficient, the envelope method has a large extraction error, and the Fourier method ignores the dispersion characteristics of the refractive index, the measurement accuracy is limited for some precise scenario. In this paper, a new film thickness extracting strategy is proposed with genetic algorithm. At first, the measured spectral reflectance of the film is used to extract the extreme value points, and an extreme value sequence is obtained by dividing their corresponding wavelengths, and then the slope of the extreme value sequence is fitted with the slope of the extreme value sequence of the preset film thickness. When the two slops are consistent, the preset film thickness is the thickness to be measured. Theoretical analysis and measuring experiments are carried out to show a stability of about 0.05nm for a 8630.11nmfilm sample, verifying the feasibility and stability of the proposed strategy.

With the continuous development in the field of optics, high-resolution and even super-resolution image processing has become key to improving image quality and resolution. However, phase unwrapping algorithms are crucial in interferometry, but their complex computational methods often lead to inefficiencies, especially as CPU integration increases. Despite this, single-thread performance is constrained by factors such as power walls, frequency walls, and instruction-level parallelism, resulting in low efficiency. To address these limitations and enhance image processing speed, this paper proposes a high-performance CPU computing algorithm based on the Goldstein algorithm, combining OpenMP technology with SIMD instructions. In the three critical steps of Identification of Residues, Branch-cutting, and Integration, tasks are divided into multiple subtasks and executed simultaneously by independent computational units within a single clock cycle, solving problems more quickly, especially during the Integration process where a new algorithm is introduced. To evaluate the optimized algorithm, we conducted multiple tests on super-resolution images. The results show that as pixel size increases, the algorithm optimized with high-performance CPU computing demonstrates significantly better performance than standard CPU computation. On an RTX 3060 laptop, using a phase map with a resolution of 9344×7000, we achieved a 13.5-fold speed improvement. Therefore, combining this algorithm with CPU parallel computing can significantly enhance the efficiency of interferometry.

Bearing is the key component of equipment manufacturing. As the core parts of bearings, bearing rollers determine the bearing performance and reliability. In advanced bearing rollers fields, they are used in high temperature, high load, and high-speed working conditions. The existence of bearing rollers surface defects will cause huge disaster. Hence, the quality inspection of bearing rollers is very important. However, the bearing rollers material is metal and there is a certain roughness on the surface. Therefore, the light scattered on bearing rollers surface by defects is complicated. Furthermore, the advanced bearing rollers shape is not exclusively cylinder. It includes cone and drum types. The direction of reflective light on surface changes with the surface position, which will cause some illumination reflective light enter into the imaging system and interfere defects inspection. To solve these problems, a surface defects scattering simulation model is built and defects inspection illumination imaging system is designed in this paper.

In the measurement of large-aperture flat, mechanical stress arises from the contact between the flat and supporting materials, which is influenced by both gravity and temperature. This stress induces surface deformation, consequently impacting the optical system's image quality. To enhance support efficacy, the finite element method was used to analyze the surface deformation of these flats across various vertical and horizontal support configurations. Distribution patterns arising from the effects of gravity and temperature on flat surface shape were also inverstigated. Analysis reveals that the use of horizontal support induces more conspicuous gravity-induced deformation when compared to vertical support. Additionally, results show that temperature has a more significant effect on flat surface deformation than gravity. The findings of this study offer pertinent insights for designing support structures for large-aperture flat and implementing temperature control measures in experiments.

This paper conducts research on the instrument transfer function(ITF) of a 4-inch Fizeau interferometer. It first introduces the concept and principle of the ITF and investigates its measurement methods. Experimental measurements and analyses are carried out on the 4-inch Fizeau interferometer, utilizing both sinusoidal grating and simulated grating to compare and analyze the test results of the ITF. Furthermore, an error analysis is conducted based on these results.

Interference measurement is a high-precision detection method for evaluating optical components and beam quality. Interferometry is commonly used for an optical element surface accurate test. But it is susceptible to interference from environmental and phase ambiguity issues. So a polarization-based method for extracting phase from dual-frame interferograms is proposed. We put forward a polarization-based method for extracting phase from dual-frame interferograms. This method only requires two interferograms with a phase difference of pi/2, which are processed using the extremum method and directly subjected to tangent and arctangent phase extraction to recover the surface shape. It enables simple and efficient extraction of the phase distribution of the tested optical element surface to be realized in a sub-millimeter scale dynamic range with a nanometer accuracy. The present invention does not require high-precision components such as phase shifters and spectrometers, and does not require preprocessing operations such as normalization and denoising of interferograms. It has the advantages of simple optical path, large measurement range, high accuracy, and high efficiency.

Utilizing the flexible material PDMS, a zoom column lens is crafted to achieve a wide focal length adjustment range and superior focusing quality. The influence of parameters such as the initial radius of curvature and lens thickness on the focal length and focusing quality is initially analyzed. By employing COMSOL Multiphysics simulation software, the impact of various initial structural parameters on the lens's focal length adjustment range and focusing quality is assessed. The proposed design method's feasibility is validated with a specific example. For a lens with an initial half-aperture of D=10mm, thickness d=2mm, and width h=4mm, the focal range extends from 38.672mm to 58.835mm, offering a considerable adjustment range of 20.163mm. Additionally, the root mean square radius (RMS) remains below 29.1 μm, nearing the diffraction limit. This design process is also suitable for selecting initial structural parameters for varying size requirements, providing an effective approach to developing zoom column lens using flexible materials.

Swift and accurate measurement of overlay errors has long been imperative for ensuring throughput and yield in integrated circuit (IC) manufacturing. At present, image-based overlay (IBO) remains the predominant method for overlay metrology, relying on Linnik scanning white light interferometry (LSWLI) to guarantee rapid and precise focus assessment. Nevertheless, the focal plane position determined by LSWLI often does not align with the optimal contrast focal plane for imaging in the IBO system. This paper proposes a method to meticulously calibrate the systematic error in focus measurement. Initially, the Fourier transform method is employed to analyze the acquired LSWLI interference curve and extract the coherence envelope, from which the center of gravity is computed to ascertain the LSWLI focal plane position. Subsequently, the gradient RMS means of the images near the LSWLI focal plane are calculated and a weighted polynomial is fitted to these values to obtain the focal plane position imaged by the IBO system. Finally, by repeating these steps and averaging the results of multiple measurements, the inherent system focus offset (SFO) is obtained. This calibration can be conducted during the equipment test and calibration stage, ensuring that even in challenging working conditions, the IBO system can swiftly and accurately determine the final imaging focal plane position by solely completing the LSWLI focus measurement and supplementing it with the SFO. This calibration method is an important reference for the practical engineering application of LSWLI in IBO focus measurement system.

Torsion balance system as a high precision important ultra-small force measurement tool usually requires ultra-highresolution deviation measurement of the torsion angle. Currently, autocollimators are used for the torsion angle deviation measurement. Optical coherence tomography (OCT) is a high-resolution three-dimensional imaging technology, which has the characteristics of real-time imaging of samples with micron or sub-micron resolution at millimeter depth, and is widely used in biomedical research and industrial detection fields. In this work, utilizing the single-mode fiber based common-path OCT system architecture, we design and fabricate a compact probe that consists of four displacement sensing fibers connected to one home-built SD-OCT system with a central wavelength of 840 nm. Each fiber senses the distance between the fiber tip and torsion balance integrated reflection mirror. The distance peaks from each fiber are designed to be distributed along system one A-scan depth which enables simultaneous measurement. With the phase sensitive reconstruction algorithm, tens of pm distance sensing resolution can be achieved. Analyzing the displacement values from four distributed spatial points, the torsion principle surface can be reconstructed for post experiment analysis. We believe our proposed work will be valuable for distributed ultra-high resolution compact and stable displacement sensing.

A low divergence angle dependent trap photodetector was designed based on two photodiodes and a concave mirror, which can adapt to measurement of both spatially collimated beam and divergent beam in a small space. To determine responsivity of the trap detector, cryogenic radiometer system is used to calibrate trap detector under the condition of collimated beam, while the angular dependence can be ignored at a certain uncertainty level. Responsivity of trap detectors based on silicon photodiodes are calibrated traceable to cryogenic radiometer, with an uncertainty of less than 0.1%. The uniformity of photodetector is measured to be about 0.03% in a 5mm×5mm sensitive area and angular dependence is less than 0.1% when the angle between the incident beam axis and the normal direction of the detector surface is less than 7 degrees. The results show that the detector with this structure has a good consistency in the response of measuring collimated light beam and divergent light beam within a certain divergence angle.

The earth's environment is strongly affected by changes in solar radiation. Accurate measurement of solar radiation is great importance to us. NIM has built a detector-based total solar irradiance calibration system. The transfer reference uses three 18mm×18mm silicon photodiodes assembled into a reflective trap detector whose power responsivity is traceable against the cryogenic radiometer. In order to avoid the saturation of the photodetector under high power, a beam splitting device is used to monitor the corrected power value. The reference trap detector and the total solar irradiance meter were placed in a vacuum chamber to calibrate the power responsivity using 532nm laser source. The aperture area of the total irradiance meter is measured by the aperture area measuring system based on the laser scanning method. The calibration uncertainty of the final total solar irradiance is 4.1×10^-4 (k=1).

Hyperspectral imaging is a spectrally resolving technology with the spatial information of an object, organizing two-dimensional image data into a hyperspectral cube according to spectral bands to provide detailed information about the measuring object. It is a versatile technique, encompassing various methods depending on the measurement approach, each with its own advantages and limitations. In this investigation, we propose a simplified hyperspectral imaging system based on phase retardation to address the shortcomings of existing techniques.

The Mueller matrix spectroscopic ellipsometer is a non-destructive measurement method that utilizes the polarization properties of light and is widely used to measure the critical dimensions created after semiconductor processing. However, for critical dimension measurement, it should use a reflective objective so that its focal length does not change according to each wavelength, and the size of the beam incident on the sample keeps sufficiently small. At this point, there is a limitation in that the polarization state changes depending on the angle of the beam incident from the reflective objective and the degree of coating on the mirror surface. In this investigation, we propose a method to extract the polarization state changes that occur in the reflective objectives.

Absolute measurement is based on the Fizeau interferometer system, which features a common optical path that mitigates the impact of system-specific errors and is less sensitive to environmental changes. Currently, methods for flat absolute measurement include: the three-plate mutual inspection method, the odd-even function method, the rotational symmetry method, and the mirror symmetry method, etc. Typically, the odd-even function method is used for flat absolute measurement, but it is commonly used and has proven effective for circular domain boundary conditions in existing absolute surface measurements. To measure and fit rectangular domain boundary conditions, this paper also utilizes Zernike polynomials and Chebyshev polynomials to fit rectangular domains, with Schmidt orthogonalization used to achieve Zernike fitting for rectangular domains, and their performance is compared.

Based on microscopic imaging, optical systems can effectively detect defects on the surface of laser gyro reflector without causing damage. However, the minimum detection size is limited by the resolution of the microscopic imaging system. To detect submicron-level defects on laser gyro reflector substrate, a surface scanning dual-source scattering measurement scheme based on scattering measurement technology is proposed. Utilizing the Finite Difference Time Domain (FDTD) method and the detection scheme, an electromagnetic scattering model of the laser gyro reflector substrate is established to simulate the characteristics of defects and the distribution of electromagnetic fields. An experimental platform for surface scanning dual-source scattering measurement is established, and polystyrene latex (PSL) spheres with a diameter of 200nm are deposited on the surface of the laser gyro reflector substrate to verify the effectiveness of the proposed method. Scattering imaging experiments in both bright and dark fields are conducted on the USAF 1951 standard resolution plate to obtain the directional characteristics of dark field scattering. Additionally, standard-sized rectangular line patterns, dots, and checkerboard patterns of 1-10μm are fabricated using reactive ion beam etching to create defect samples of photomask patterns, and scattering imaging experiments are conducted on these samples to obtain the detection distribution of bright field patterns. The results indicate that the system can achieve a detection resolution better than 175nm. This method provides a reference for the detection of substrate in inertial guidance systems.

Schlieren technique is widely used in the visualization and measurement of combustion fields due to its high sensitivity. The data obtained by single-direction schlieren imaging is limited. With the improvement of measurement requirements, schlieren computerized tomography (CT) has become an important research direction. Schlieren CT reconstructs the test field from multidirectional projections. Due to inevitable system installation errors, the projections will be imaged at different positions on the sensors with different light intensities. In this paper, a parallel transmission schlieren CT system is designed with six directions. In order to solve the above problems, firstly, a multidirectional calibration method of schlieren CT based on affine projection is proposed to determine the internal and external parameters of the system. Then, the calibrated schlieren technique is used to establish the quantitative relationship between the grayscale values of the multidirectional schlieren images and the light displacements. With the calibration results, projections can be remapped to a unified coordinate system to reconstruct the three-dimensional distributions of the flow field.

In the integrated chip industry, there is a growing demand of defect detection, and the autofocus capability of microscopy can significantly enhance efficiency. This paper presents a novel technique based on an autofocus methodology known as the eccentric light beam approach. Specifically, we have developed a line-stripe-shaped laser beam projection system that uses a linear array CCD, offering high resolution and instant response. The simple design of the linear array CCD overcomes noise interference caused by system processing tolerances and reduces signal processing complexity. In accordance to the proposed system, we designed a novel algorithm called adaptive multiscale windowing to calculate the centroid of the linear array image which is an essential criterion of the defocus value. Additionally, we explore the relationship between sample defocus amount and the centroid position shift of the received signal. We build the motion part with the resolution of less than 1 micron and response speed of less than 100 milliseconds. From the experiments conducted, we achieved the accuracy of less than 1 micron and the focusing speed within 0.2 second.

Cylindricity is a key parameter to describe the accuracy and quality of the small-size cylindrical parts. Cylindrical parts such as needle roller bearing is widely used as a core part in RV gearboxes, hydraulic pumps and other mechanical components, and the geometric accuracy of the needle roller affects the performance and service life of the mechanical product. The small-size cylindrical part is also used as precision standard part to help measure and position. The cylindricity error can propagate with the manufacture and assemble process. Therefore, the cylindricity is of great significance in the fields of industrial robots, aerospace, medical devices, and so on. It is necessary to evaluate the cylindricity of the small-size cylindrical part and analyze the measurement uncertainty to guarantee the geometric accuracy and improve the device performances.

Non-contact cylindricity measuring of the small-size cylinder is investigated by the chromatic confocal sensor in both relatively fixed and unfixed manners. The uncertainties of the both cylindricity measurement systems need to be analyzed and compared. When applying both measurement systems, the measuring accuracy is negatively affected by angular misalignments of the small cylinder and the measuring light source when the linear scan method is used. When the unfixed scheme is applied, the motion error of the precise translation stage has negative impact on the scanning process. The mounting and distribution error of the light spots effect the scanning coordinate precise when using the fixed scheme. The different sources are discussed respectively. According to the uncertainty result of the coordinates, a measurement uncertainty analysis is carried out through numerical calculations based on a Monte Carlo method. Proven by the experiments, the final result shows the fixed line spot manner has advantages in accuracy due to the better stability of the measurement system.

In modern scientific research and industrial applications, the rapid, automated, and accurate measurement of micro-liquid volumes added to reaction or detection containers is a critical need. Traditional methods for measuring micro-liquid volumes often suffer from insufficient accuracy, low stability, and are prone to interference from bubbles between microliquids and residual droplets in the transmission pipelines. To address these issues, this paper proposes an automated microliquid metering method and system based on machine vision. The system comprises optical imaging units, drive control units, image processing units, metering algorithm units, and calibration units. By optimizing the optical imaging setup, the brightness and contrast of the liquid in the metering field are enhanced, ensuring the accuracy of the volume measurement. Additionally, image processing algorithms are employed to segment the liquid section, and its length in the pixel coordinate system is extracted as a representation of the volume, effectively eliminating the interference from bubbles in the image. Finally, calibration-based measurement methods and direct measurement methods based on homography matrix scale transformation of marker points achieve metering accuracies of 98.2% and 98.3%, respectively. Compared to traditional industrial micro-liquid metering methods, this approach effectively overcomes the impact of bubbles on measurement accuracy while offering greater stability and reliability.

Laser processing of micro-via arrays is a critical technology in the electronic packaging industry, essential for the rapid, non-destructive inspection of the geometric shape and depth of blind vias. As chip packaging processes trend towards higher density and miniaturization, the demands on blind via array detection technology are increasing. This paper proposes a fast blind via array inspection method based on dispersive spectroscopy confocal technology. By mounting the probe on a three-axis kinematic stage, auto-focusing is achieved, enabling rapid scanning imaging over a 10 mm × 10 mm area to acquire 3D point cloud data.

We have developed an effective algorithm to filter noise from the 3D point cloud data and align the line scan data, reconstructing accurate geometric profile information of the blind vias with sub-micron inspection accuracy. Tested on copper-clad board blind via arrays, this method quickly and accurately detects the geometric parameters of blind vias, providing a powerful tool for real-time monitoring of blind via processing quality and a novel solution for quality control in electronic packaging, including BGA packaging. The method offers advantages such as fast measurement speed, wide measurement range, and non-destructive, non-contact operation, with broad application prospects in the electronics manufacturing industry. Compared to existing technologies, our proposed measurement method is faster, offers higher resolution, and covers a wider measurement range, meeting the increasing requirements for blind via detection in future chip packaging processes. Furthermore, this technology can be extended to size and morphology inspection in other micro-nano processing fields, offering significant theoretical and practical value.

The piezoaxionic effect was recently proposed to introduce a possible solution ensuring the detection of an elementary particle called axion predicted by theory. With our experience in research on the improvement and characterization of quartz oscillators and other materials allowing the propagation of acoustic waves. We are interested in contributing to the improvement of the precision of measurement means to determine if it is possible to have sufficient sensitivity for detecting effects of elementary particles which would be characteristic of dark matter. This potential effect of axions manifests through acoustic waves. We are interested in knowing the parameters which could potentially be a source of complications for this detection. This involves being able to estimate the knowledge of the accuracy and frequency stability used and the uncertainty terms which could affect the construction of an experimental device. Different piezoelectric materials are considered as candidates to help to highlight this piezoaxionic effect. We propose to present this work during the conference.

Under storage, a phenomenon known as drive level dependency (DLD) or drive level sensitivity (DLS) may appear that prevents the starting of oscillation. Limits of the best oscillators based on this type of piezoelectric materials are known. As well as we remind about various experimental set-ups, and measurement procedures used to obtain very low drive level motional parameters, we are interested in investigating different designs and topologies to ensure stable solutions. Understanding the problem of starting piezoelectric oscillators after a long storage period may help for settling optimized devices to understand origin of noise. We are not only interested in the description of phenomena from the point of view of electrical or optical schematization, but concretely in implementing solutions to resolve them and find lasting technological solutions.

The fisheye lens, with a field of view (FOV) angle reaching 180 degrees, is highly effective for visual inspection and measurement of large scenes, provided it is accurately modeled and precisely calibrated. Unlike perspective projection lenses with narrower FOVs, fisheye lenses exhibit stronger nonlinearity, greater distortions, and more pronounced aberrations. Moreover, the calibration accuracy of current state-of-the-art imaging models and methods is generally less than 1/10 of a pixel, which fails to meet the high-precision requirements of certain measurement scenarios. In this paper, we introduce a new imaging model and calibration method for fisheye cameras. Supplementing traditional projection and distortion models, we propose image-variant intrinsic orientation parameters to account for the influence of the camera's attitude on intrinsic parameters. Additionally, we develop a corresponding bundle adjustment algorithm for this model. Because traditional calibration objects are too small to meet the high-precision needs of fisheye lenses, we establish a large planar calibration field with numerous control points and capture a series of images from various orientations for bundle adjustment calibration of the imaging model. To address the significant impact of initial parameter values on the bundle adjustment convergence process, we present a new calibration method that enables automatic processing and matching of calibration image data, ensuring robust and reliable results. Calibration experiments using a NIKON D810 camera and a Nikkor 16mm fisheye lens demonstrate that our method achieves a calibration precision of 1/15 of a pixel, surpassing other models and methods reported in the literature. Furthermore, our proposed method is distinguished by its simplicity in operation and automated data processing.

This paper aims to address the limitations of traditional methods in adaptability and reliability by enhancing the precision of goods counting in logistics warehousing environments. Recent advancements in deep learning offer promising solutions to these challenges. Leveraging visual technology, our study proposes enhancements to the A Low-Shot Object Counting Network With Iterative Prototype Adaptation (LOCA) counting network. Specifically, we introduce the aspect ratio as a new feature for extraction, which enhances the model’s capability to capture object characteristics effectively. In the image feature extraction module, vision mamba is introduced to compress visual representations using a bidirectional state space model(SSM). Furthermore, we augment the loss function by integrating the Structural Similarity Index (SSIM) alongside the existing Mean Squared Error (MSE) loss. This augmentation enables the model to maintain pixel-level accuracy while preserving crucial structural information within the images. The experimental results on the test set demonstrate a significant enhancement in Mean Absolute Error (MAE) metrics(over 30%) and Root of Mean Squared Error(RMSE)(over 30%) , thereby validating the effectiveness and generalization capability of the enhanced model. Notably, the introduction of vision mamba, aspect ratios and the SSIM loss function contributes to the model’s improved performance, facilitating more accurate and reliable goods counting. The dataset used in this study originates from real-world warehouse environments, comprising over 1000 annotated images. These annotations encompass two types: points and bounding boxes, which play a crucial role in the development of few-shot counting models. By integrating these innovative features and loss functions, the enhanced model offers a more accurate counting solution for warehouse goods, showcasing potential applications in achieving high-precision inventory audits.

As robotics advances, visual SLAM technology gains traction. Monocular inertial SLAM is notable for its affordability and real-time capabilities. Researchers introduce line features to enhance traditional point-based SLAM in scenarios like weak textures or motion blur. However, mainstream methods, combining LSD and LBD, suffer from high computational demands, impacting real-time robot localization. To address this, we propose a monocular inertial SLAM method using enhanced ELSED and imu-aided line optical flow. We replace LSD with improved ELSED, boosting line feature extraction speed. Additionally, our imu-aided approach enhances line feature tracking accuracy and matching precision. Comparative experiments with mainstream methods validate the effectiveness of the proposed method.

Helical surfaces are important elements of solid end mills. Their production is carried out using multi-coordinate grinding. Shape errors and reduction in the quality of the screw surface appear due to abrasion, high pressure, and wear of the grinding wheel. Therefore, it is extremely important to measure geometric accuracy, to perform linear and angular measurements, and to study the properties of rake helical surfaces. The paper proposes improvements to monitoring of helical surfaces via the use of a new computer vision system for assessing microtexture on helical surfaces after multiaxis grinding on CNC machines. A computer vision system was developed to evaluate defects on helical surfaces after multi-coordinate grinding on CNC machines, and a comprehensive analysis of existing indicators for recognizing the defect was carried out in a guaranteed range of probability of finding a solution of 99.7% for the distribution density of grinds. To verify the developed method, the accuracy of surfaces obtained by using the one was compared with the measurements carried out using specialized equipment for the control of the accuracy of helical surfaces. A new system for monitoring the accuracy and defects of cutting edges, helical front and rear surfaces allows establishing the main geometric parameters of the cutting edges and cutting wedge such as flute angle and rake angle at the apex using key indicators of the difference in color intensity in the focal zone of the image. When developing this approach, it was found that areas with smaller curvature of the rake surface are more susceptible to the accumulation of helical flute pitch errors after grinding. Experimental studies of the system operation were conducted to provide empirical evidence on helical surfaces after multiaxis grinding on CNC machines, demonstrating excellent convergence and defect recognition accuracy. The accuracy of determining the results of the inclination angles of the microtexture surface after grinding at the control point is 2-2.5 degrees, which allows you to form a comprehensive solution for scanning the surface, which will allow you to apply a simple method of control using a camera in reflected light.

For SERF magnetometer, slow diffusion is one of the key operations required to achieve multi-channel and multi-axis measurement. Small diffusion distance over a polarization lifetime allows for the measurement of each separate region of a singular cell to be considered independent. Especially for multi-channel measurement, the spatial resolution is mainly limited by the diffusion distance, which is positively correlated to the diffusion constant. Therefore, the precise determination of the diffusion constant is significant for further optimization of the magnetometer’s spatial distribution and beneficial for improving the performance of spatial resolution. Herein, we proposed an in-situ measurement method of diffusion constant under large-scale cell condition in dual-beam magnetometer. With consideration of the diffusion effect, we established the distribution of polarization in the plane vertical to the pump beam. Then we analyzed the dependence of the optical rotation angle on the diffusion constant and the pump beam facular radius from both experiment and numerical simulation perspectives. Based on this, we realized the in-situ measurement of the diffusion constant through the detection of the optical rotation angle under different pump beam facular radii. In our experiment, we adopted a pump beam with great optical power to sufficiently polarize the alkali atoms and derive the diffusion constant at 1.6 cm2/s through formula fitting. This method can achieve an in-situ measurement of the diffusion constant and be generally applied to different cell conditions or measurement modes. Furthermore, it can provide guidance on further improvement in the spatial resolution of SERF magnetometer in multi-channel measurement, as well as the distribution of pump or probe beam in multi-axis measurement within a singular cell.

Image segmentation is the critical step in different imaging and especially optical inspection applications: detection and recognition of objects, classification, analysis, and identification. Also, image gradient, as a preprocessing step, is an essential tool in image processing in many research areas, such as edge detection, segmentation, inpainting, etc. However, these tools have limitations and could be more accurate since the capture devices usually generate low-resolution images, which are primarily noisy and blurry. It is critical to receive useful gradient estimation on noisy color images while preserving the sharp edges. In the present paper, we develop a new gradient by integrating the quaternion framework with local polynomial approximation and the intersection of confidence intervals based on anisotropic gradient concepts for color image processing applications. We apply the proposed gradient technique in a modified active contour method to perform an automated segmentation for optical inspection applications. Computer simulations on the segmentation dataset for optical inspection applications show that the new adaptive quaternion anisotropic gradient exhibits fewer color artefacts than state-of-the-art techniques.

This article proposes a problem statement and its solution for finding a point equidistant from objects in three-dimensional space. The article considers an approach to determining the possible trajectory of a given object in an assumed threedimensional space R³, in which there are static 3D objects that impede the movement of the given object. A computer vision system is used for spatial positioning. To determine the point of displacement of the object's trajectory in space, a solution to the problem of searching for optimal trajectories on planes that do not intersect or touch the boundaries is proposed. The article discusses an algorithm for solving this problem and provides examples of determining optimal trajectories in a curved surface using the method of multicriterial interpolation of curves, with a given discretization step. The generation of a data set for a curved surface (point cloud) is described. Examples of searching for the hovering point of an object in the absence of its contact with external boundaries are given. An example of searching for an equidistant point in space with simple-shaped objects is given on a test data set, and recommendations are given for their use in robotic systems.

Ultraviolet radiant exposure meter, also known as UV energy meter, is widely used in a multitude of fields, such as sterilization, climate change, solar photovoltaic, material aging, medical health, UV curing, lithography and so on. Ultraviolet exposure radiation meter is a commonly used instrument to measure ultraviolet radiation. Due to the particularity of the structure and the complexity of the influencing factors, the measurement error of commercial instruments is very high. Commonly used ultraviolet light sources include mercury lamps, LED light sources, metal halogen lamps and so on. This paper will study the calibration method of the ultraviolet exposure radiation meter, and evaluate the measurement uncertainty.

This paper uses an in-band optical performance monitoring (OPM) method based on autocorrelation, offering high sensitivity and multi-damage monitoring. The proposed method effectively detects both optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD) across a broad range of cumulative dispersion values. Utilizing the Wiener– Khintchine theorem, we retrieve the autocorrelation of signals through spectrum retrieval without the need for phase-matched second-harmonic generation. Dispersion is determined through variations in the autocorrelation function curve after cross-phase modulation (XPM), while OSNR is determined based on the normalized autocorrelation function and the characteristics of noisy signals. Simulation results demonstrate the robustness of this method across various modulation formats and input optical power levels. For 32 Gbaud signals, the OSNR monitoring error remains below 0.5 dB, with an effective monitoring range extending up to 30 dB. Additionally, the dispersion monitoring range reaches 800 ps/nm, confirming the broad applicability of this approach for high-capacity optical systems.

This paper introduces a new absolute distance measurement system. A single-cavity double-comb laser based on single-wall carbon nanotube mode-locking is used as a light source by adjusting the intraccavity loss, and two optical combs with slight differences in wavelength and repetition rate and constant repetition frequency difference are generated for absolute distance measurement based on asynchronous optical sampling. The measured fuzzy distance is about 1.5 meters, and the measurement uncertainty is 15μm.