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Femtosecond laser processing is a non-thermal process with less heat effect on a target material and is applied to dielectric and difficult-to-machine materials, such as titanium alloy and diamond. Femtosecond laser processing has been used for 3-dimensional shape generation in recent years, and increasing accuracy and productivity are required for such generation by femtosecond lasers. However, a 2.5-dimensional computer-aided manufacturing (CAM) system, which is mainly used in femtosecond laser processing, does not satisfy the requirement for complicated 3-dimensional shape generation. Therefore, there is a need for the development of a 3-dimensional CAM system for high-precision and productive 3-dimensional processing. Furthermore, for the 3-dimensional CAM system, quantitative identification of a 3-dimensional removal shape through ablation is necessary. This study proposes the development of a simulation method to accurately predict the 3-dimensional removal shape through femtosecond laser processing, including the piecewise approximation of the ablation rate and absorptance correction. At the same time, a similar 3-dimensional shape as that found through the experimental results was obtained during the simulation by considering the mechanical errors of the laser processing machine in the simulation model. Furthermore, an on-machine measurement system was developed to efficiently identify the ablation parameters.

Simultaneously and independently measuring two-dimensional (2D) displacement, one-dimensional (1D) for out-of-plane measurement and 1D for in-plane measurement, is important for practical applications. Although extrinsic fiber Fabry-Perot interferometers (EFPIs) have been reported for highly precise out-of-plane displacement measurements for many years, simultaneous measurement of 2D displacement with submicron accuracy has not been realized by a monolithic EFPI as far as we know. In this paper, a monolithic dual-cavity EFPI to realize 2D displacement measurement of a target is reported. By quantitatively analyzing and experimentally calibrating the linear dependences of the in-plane displacement sensitivity and interception on the cavity length, the effect of out-of-plane displacement on the in-plane displacement measurement is removed, which is the basis of the 2D displacement detection. 2D random movement detection and the repeatability of the system are investigated experimentally. Within the range of 10m for in-plane displacement, and 352m-358m for cavity length, demodulation errors better than 96nm are achieved. The 2D displacement measurement system based on the dual-cavity EFPI with the advantages of noncontact, high accuracy and compact size is promising to be applied in the 2D acceleration measurement, 2D rotor vibration measurement, 2D precise positioning in semiconductor manufacture, thermal expansion coefficient measurement, and so on.

The accuracy in the measurement of magnetization curve (M-H) for soft materials is easily influenced by the external static field in the unshielded environment. To eliminate the influence from the environmental field, the measurement system must be placed in a zero-gauss chamber. However, such a device is not widely available and also costly. In this work, the rapid M-H measurement system with a giant magnetoresistance (GMR) sensor serving as the zero-field detector is proposed. The M-H curve is obtained by integrating the voltage in the pickup coil to determine the magnetization of the test sample under a sweeping magnetic field. The environment field component along the direction of the sweeping field is suppressed by using the output of the GMR sensor as the trigger signal to determine the offset field in the measured M-H curve. The experimental results show that the M-H curves for various kinds of soft magnetic samples, e.g. mu-metal wire, can be obtained under the interference of an applied static field. The proposed method helps improve the accuracy of the rapid M-H measurement system in the unshielded environment.

In this study, we developed a neutron time-of-flight (nTOF) measurement system for a 1.7-MV tandem proton accelerator with a target covered with 300-nm-thick lithium (Li) layer. With implementation of beam chopping module after its ion source, the accelerator is configured to operate in pulsed-beam mode with a pulse width

International audience; We have measured the three-dimensional coordinates of retroreflecting glass spheres using a multilateration technique. To this end, the distances between each target and our measurement heads have been determined by an in-house prototype of electro-optical absolute distance meter. The used targets are spheres of glass refractive index n=2 and of diameter 14.2 mm. They offer a much larger aperture than corner cubes and a lower cost, but they present a low reflectivity. However, this paper shows that with a proper collimation of the laser beams it is possible to reach a range of operation of 20 m. The standard uncertainty on such distances is better than 11 µm, including the mechanical errors of the gimbal mechanisms of our aiming systems. This uncertainty has been validated thanks to a comparison with an interferometric bench. In addition, the measurement of the coordinates of 16 glass spheres using a self-calibration multilateration algorithm has also confirmed the performances of the developed system: the standard deviation on the position errors has been estimated to about 10 µm.

A photonics-based system for simultaneous angle of arrival (AOA) and frequency measurement is proposed and demonstrated. In the proposed system, an acousto-optic modulator (AOM) based optical frequency shift loop (OFSL) is used to generate an optical frequency-stepped local oscillator (LO). After balanced in-phase and quadrature (I/Q) down-conversion with the frequency-stepped LO, the frequency to be measured is obtained. Thanks to the balanced I/Q down-conversion, the image frequencies and undesired frequency-mixing components can be suppressed, making the system have better adaptability to multiple-target scenarios. In addition, the AOA from different RF sources can also be estimated based on the Van CittertZernike theorem, even if the working bands of these targets overlap with each other. In the proof-of-concept experiment, the measurement of multiple targets with different frequencies is achieved by frequency detection with 0.179 MHz resolution. Moreover, incoherent microwave sources at the same frequency band can also be distinguished in the angular direction, achieving the capacity of simultaneous frequency and AOA measurement of multiple-target.

A distributed pressure sensor is proposed and designed for dynamic pressure measurement by using frequency-agile fast Brillouin optical time-domain analysis (BOTDA). A double coated single-mode fiber (SMF) is used as the sensing fiber because of its 1500- $\mu \text{m}$ thickness outer coating that can significantly improve the dependence of the Brillouin frequency shift on pressure. Then, the frequency-agile technique is used to generate frequency-agile pump pulse in BOTDA system so that a fast Brillouin gain spectrum distribution measurement can be achieved. An injection locked scheme is used as both optical filter and optical amplifier to improve the measurement accuracy. As a result, the static pressure sensitivity of the double coated fiber is −3.46 MHz/MPa with the pressure ranging from 0 to 30 MPa. Subsequently, a large dynamic range pressure measurement is performed with a sampling rate of 33.3 kHz and maximum sensing distance of 25 m. Furthermore, it is proved that the uncertainty of dynamic pressure measurement system is 0.03 MPa.

Confocal microscopy is high precision and widely used method for topography measurement. The surface height information is obtained by peak extraction of the axial response signal (ARS) which axial tomography of the surface is required. Therefore, when scanning large-diameter surfaces with a confocal coordinate measuring system (CCMS), the relative horizontal scanning trajectory (RHST) between the confocal sensor and surface is repeated and time-consuming step motion, which greatly increases the measurement time. To improve the scanning measurement efficiency of CCMS, we propose a new location tracking scanning (LTS) method based on multi-focus. In the LTS method, the RHST is a continuous linear motion during the process of axial tomography, and the horizontal motional surface is located and tracked through a series of focuses to restore the ARS. A generatrix profile of a spherical surface is measured to verify the effectiveness of the proposed method, and the results show that the scanning measurement time can be reduced by more than 90% without loss of accuracy of the profile measurement.

We present a portable Rydberg-atom-based radio frequency (RF) electric ( $E$ ) field measurement instrument (Rydberg field measurement system or RFMS). The RFMS comprises an atomic RF field probe (RFP) connected by a ruggedized fiber-optic patch cord to a portable mainframe control unit. The unit includes a software interface providing self-calibrated SI-traceable RF measurement and analysis, including real-time field and measurement uncertainty readout and spectral RF waveform visualization. We characterize the RFP and measure polar field and polarization patterns along primary axes of the RFP at 12.6 GHz, obtained by rotations of the RFP in the far-field of a standard gain horn antenna. Field pattern measurements at 2.5 GHz are also presented. The measured field patterns are in good agreement with finite-element simulations of the RFP, establishing that the atom-based RF $E$ -field probe is well-suited for SI-traceable RF measurements over multiple bands. A one-time calibration procedure and an uncertainty analysis are introduced and implemented, as required for practical atomic probe designs to realize absolute-standard SI-traceable measurement capability. This includes uncertainty contributions from the atomic-spectroscopy measurement method and analysis and from the material, geometry, and hardware design. Simultaneous RF field and polarization measurements are demonstrated. RF waveform measurement is demonstrated using example pulsed and modulated RF signals.

We develop a high-speed interrogation system with a wavelength-swept laser for sensing multiplexed fiber Bragg gratings (FBGs). High-speed and multipoint sensing is achieved by means of a buffered Fourier domain mode-locked (FDML) laser, a recently proposed high-speed wavelength-swept laser. This laser increases the measurement rate several times by tailoring the laser output with a buffer stage. The developed buffered FDML laser successfully achieves a measurement rate of 202.8 kHz using a general FDML laser driven at a sweep rate of 50.7 kHz. In order to detect reflection signals of FBGs at the high measurement rate, the measurement system introduces digital signal processing using a field programmable gate array (FPGA). However, FBG measurements with wavelength-swept lasers are affected by the propagation time (delay) in the optical fiber connecting from the laser to the FBG sensor, which reduces measurement accuracy. To overcome this limitation, the developed system uses a delay correction method with bidirectional sweep of the buffered FDML laser. The interrogation system with the buffered FDML laser achieves a time resolution of $4.9~\mu \text{s}$ without being affected by the delay.

For the purpose of realizing the dynamic angle measurement and calibration of the inertial equipment (such as rotary table), a dynamic angle measurement system based on the autocollimator and the fiber optic gyroscope (FOG), which can be used as an angle standard device, is designed in this paper. In this system, the scale factor of the FOG can be calibrated in the field application based on the autocollimator with the precision of $1^{\prime \prime }$ in the range of ±0.05°. Furthermore, the angle measurement deviation between the FOG and the rotary table can be limited in $\pm 3^{\prime \prime }$ when the scale factor of the FOG is calibrated by the autocollimator when necessary. This research can guarantee the long-term accuracy of the scale factor of the FOG in the field application and it will greatly promote the applications of the FOG as an angle standard device in the field of dynamic angle measurement.

In this article the accuracy of the LRM+ calibration is compared to that of the benchmark NIST multiline TRL procedure for the first time. The comparison is performed on NIST verified GaAs coplanar waveguide calibration reference material 8130. The NIST calibration comparison method is used to quantify the difference between measured S-parameters corrected by NIST multiline TRL and an advanced LRM+ calibration. The worst-case error bounds for LRM+ corrected S-parameter measurements are determined up to 110 GHz. It is demonstrated that the difference between benchmark multiline TRL and LRM+ is comparable with the measurement system drift. Verification results prove that LRM+ can be successfully used for accurate GaAs on-wafer calibration with customized standards. This overcomes some drawbacks of multiline TRL while providing the same calibration accuracy.

The calibration of machine tools or industrial robots needs high precision 3-dimensional coordinate measurements. Common available systems still have the need of ambitious and time extensive processes to fulfill the requested requirements. Therefore there is a strong request for fully automated systems that allow an autonomous and easy to handle procedure for 3D volumetric deviation measurements. This exactly is the intension of the here presented 3D Coordinate Measurement System. The so called µ-GPS System is based on reliable white light interferometer and robust technology. The 3D coordinates are determined via trilateration from three measured distances like it is known from the global GPS. Mainly two parts, the sensor unit (transceiver unit) including the emitter and the reference base (three cat’s-eyes) which includes the three reflectors are mounted in the workspace of the machine. A model to evaluate the signals was developed which allows in combination with a 3-dimensional failure correction a 3D accuracy of more than 5 microns. This application will be the base for an exemplary and fully automated calibration process of Swiss-type turning machines. As these machines are used in high volume manufacturing for precision parts, they need to be assembled and calibrated very accurately. For the long term stability the µ-GPS System can be easily assembled in the Swiss-type turning machine so that thermal deviations and abrasion can be measured and compensated in the control. The robust and easy handling of the µ-GPS System later allows an expansion of the showcase to robots and other machine tools.

We demonstrate a single-shot uniaxial 3D profilometry system that illuminates a sample with a structured polarization pattern and measures the reflected full-Stokes polarimetric image. Some non-contact 3D measurements require evaluating samples located in a protected environment. For example, this may be a sample under the lid of an acrylic Petri dish, a sample that has a protective film overlay, or products housed inside a plastic container. To deal with these cases, we adapt our measurement system to capture the complete polarization state using a single-shot full-Stokes imaging system consisting of two polarization cameras. This system cannot only measure the dynamic 3D shape at video rate, but can also compensate for any birefringent layers between the illumination arm and the sample under measurement. We present the measurement principles of the system and show the results of a real-time 3D profilometry experiment in which a sample was measured under the lid of an acrylic Petri dish.

The composition, operating principle, and metrological characteristics of GET 130-2019, the State Primary Special Standard of the unit of length in the field of measurements of deviations from straightness and flatness, are described. Results of investigations of the metrological characteristics of the interference measurement system incorporated into GET 130-2019 by means of which reproduction of the unit is realized on the basis of the fundamental physical constants and the properties of matter (interference) are presented, thus eliminating any additional instrumental sources of errors (uncertainty). Transmission of the unit of length in the region of measurements of deviations from straightness and flatness in the range 0–50 μm with length of the measured surface up to 30 m is achieved with the highest accuracy attainable in Russia. Comparisons that were carried out demonstrate that the metrological characteristics of GET 130-2019 correspond to the level of precision of foreign standards in measurements of deviations from straightness on a length up to 30 m and to the measurement capabilities presented in the database of the International Bureau of Weights and Measures.

A method for optimizing the wavefront errors of detected radiation in the optical system of a large-sized telescope (LST) based on the redistribution of errors over the image field is developed. On the example of a cryotelescope having a diameter of 12 m, the problem of optimizing a uniform distribution of aberrations over the image field in an LST was solved by varying the parameters of the secondary mirror in the Zemax-EE software package. The results of calculating optical assemblies using the traditional method and the proposed method for optimizing the errors of the radiation wavefront are presented. The advantages and disadvantages of both methods are considered.

Aiming at the problem that the lattice feature exceeds the view field of the scanning electron microscope (SEM) measuring system, a new lattice measuring method is proposed based on integral imaging technology. When the system works, the SEM measuring system is equivalent to an integral image acquisition system. Firstly, a lattice measuring method is researched based on integral imaging theory. Secondly, the system parameters are calibrated by the VLSI lattice standard. Finally, the value of the lattice standard to be tested is determined based on the calibration parameters and the lattice measuring algorithm. The experimental results show that, compared with the traditional electron microscope measurement method, the relative error of the measured value of the algorithm is maintained within 0.2%, with the same level of measurement accuracy, but it expands the field of view of the electron microscope measurement system, which is suitable for the measurement of samples under high magnification.

During the research phase of acrylic panel for the Jiangmen Underground Neutrino Observatory (JUNO) central detector (CD), the darkroom transmittance measurement system (DTMS) was designed and built, and a massive amount of measurements were carried out to help determine the composition and processing techniques of the acrylic panel. The mass production of acrylic panels was started after the pilot production. The requirement of transmittance measurement put forward new demands on operation, and a new measurement system was considered to support removable and non-destructive measurement on site. After the accomplishment of design, development and verification were completed, the laser measurement system came into use in the acrylic workshop of Taixing Donchamp Acrylic Ltd, and the transmittance results of acrylic spherical panels met the requirement of JUNO. The optical design, tooling design, data processing interface and uncertainty analyses of the laser measurement system are discussed in detail, and the measured transmittance results are also introduced in this article.

Most thickness measurement techniques using X-ray radiation are unsuitable in field processes involving fast-moving organic films. Herein, we propose a Compton scattering X-ray radiation method, which probes the light elements in organic materials, and a new simple, non-destructive, and non-contact calibration-free real-time film thickness measurement technique by setting up a bench-top X-ray thickness measurement system simulating a field process dealing with thin flexible organic films. The use of X-ray fluorescence and Compton scattering X-ray radiation reflectance signals from films in close contact with a roller produced accurate thickness measurements. In a high-thickness range, the contribution of X-ray fluorescence is negligible, whereas that of Compton scattering is negligible in a low-thickness range. X-ray fluorescence and Compton scattering show good correlations with the organic film thickness (R2 = 0.997 and 0.999 for X-ray fluorescence and Compton scattering, respectively, in the thickness range 0–0.5 mm). Although the sensitivity of X-ray fluorescence is approximately 4.6 times higher than that of Compton scattering, Compton scattering signals are useful for thick films (e.g., thicker than ca. 1–5 mm under our present experiment conditions). Thus, successful calibration-free thickness monitoring is possible for fast-moving films, as demonstrated in our experiments.

In this paper, we propose a fiber optic system to measure the changes in the RGB composition of light in liquid solutions using a plastic optical fiber (POF) as an intrinsic sensor. The measurement system is composed of a 3 W white light-emitting diode as the light source, a 20 cm long U-shaped POF, and an RGB photodiode array that allows us to detect the changes in the RGB composition of the light propagating through the POF. The U-shaped POF has a length of 5 mm without coating, which remains in contact with the liquid solutions. The tests were performed with different concentrations of a mixture of tequila and water. The results obtained with the RGB photodiode array showed that the system has a resolution of 0.39 % and a color change sensitivity of 0.1, 0.6, and 0.4 8–bits/% of sample for red, green, and blue colors, respectively. These results will allow us to design a low-cost prototype to measure the amount of adulteration in liquids.

In this paper, a static multi-longitudinal mode laser self-mixing absolute angle measurement system is developed to accurately monitor the deflection angle. The experimental results show that this multi-longitudinal mode laser angle sensor is capable of effectively measuring the deflection angle of the vertical dihedral mirror. The angle-measurement range and resolution of the self-mixing experimental sensing system can be obtained as ±22.0° and 0.008°, respectively. Furthermore, in-depth analysis of the angle-measurement error and related error sources are performed, of which the absolute error is less than 0.37° that demonstrates the good reliability and practicality of the self-mixing angle sensor.

In this paper, we propose a measurement system based on single autocorrelation technology and combined with LabVIEW software platform to realize the real-time online measurement of the femtosecond-laser pulse width. The system uses an experimental device based on the Mach–Zehnder interferometer, where the second-harmonic signal of femtosecond laser is obtained by the nonlinear effect of light and nonlinear material; the linear grayscale conversion, median filtering, and threshold segmentation are also applied to the second-harmonic signal. The image centroid, autocorrelation curve, and femtosecond-laser pulse width are obtained, using LabVIEW software. In the experiment, a seed laser source with a central wavelength of 800 nm is used as a test object, and the pulse width is measured to be equal to 261 fs.

This article presents a standard field generation system with an antenna for the calibration of a Ka-band electric-field probe. We constructed a measurement system having capability of not only rotating the azimuth angle of the probe but also changing the separation distance between the antenna and the probe. As a result, the orientation and separation distance of the probe can be suggested for minimal variation of the measurand, which reduces the overall uncertainty. For traceable electric-field strength measurements, we measured the associated quantities of the power, antenna gain, and impedance of the individual components constituting the field generation system. An evaluation of the uncertainty of the components providing traceability to the system was also conducted. The system is expected to generate a standard field higher than 10 V/m in the frequency range of 26.5–40 GHz. Uncertainty in the correction factors is quantified to determine the factors that affect the calibration, and the expanded uncertainty of the standard field generation system is found to be 5.1% at 26.5 GHz and 5.3% at both 33 and 40 GHz.

The axial spacing measurement between optical elements is of great significance to the positioning and adjustment of precision optical systems. Aiming at the problems of complex dispersive objective lens structure and small dispersion range in the existing dispersion confocal measurement system, a method for measuring the axial spacing of optical elements based on the method of polarization diffraction dispersion confocal was proposed. The axial dimension of a traditional refractive confocal lens with a few hundred millimeters and the complex alignment requirements were simplified to a single-chip lens with a few millimeters, which simplified the system structure. The results of lens spacing and thickness measurement experiments show that the spacing measurement error is 10 μm.

In this article, three frequency independent optical paths are designed and analyzed. A two-parabolic-mirror system and a four-parabolic-mirror system are studied and developed over 140–220 GHz to achieve precision complex permittivity measurements of a dielectric substrate. To achieve a wide plane wave zone for the center of the four-parabolic-mirror system, two 80-mm-length corrugated horns are designed and fabricated for the measurement systems. The Gaussicity of the corrugated horn is larger than 97.4%. For the multiple reflection model and direct wave model, two closed-form expressions of loss tangent are derived from the transmission parameters (insertion losses) of the measurement systems. Meanwhile, the resolution and uncertainty of loss tangent can be calculated according to the working frequency, the thickness of the wafer, the real part of the relative permittivity, and the $| {{S_{21}}} |$ measurement uncertainty. The complex permittivity of the Rogers/Duroid series PCB substrates, which are commonly used at microwave frequencies, and silicon wafers are measured in G -band.

Polarization measurement has found applications in many fields ranging from quantum science to our daily life. However, traditional polarization measurement systems suffer from large volume and high cost. To keep pace with the continued device miniaturization and system integration, new detection approaches and devices are desirable. The marriage between optical metasurfaces and superposition of optical vortex beams has offered a new idea method for polarization detection. We propose and experimentally demonstrate a single metasurface for polarization measurement based on the superposition of optical vortex beams. The relationship between the three parameters of the polarization state and the interference pattern of vortex beams is deduced theoretically. The major axis, ellipticity and handedness of a polarization state are determined by analyzing the intensity patterns of the superimposed vortex beams. Our method has provided a new approach for the development of compact optical devices for polarization measurement.

In order to simultaneously obtain the thickness and refractive index for each layer of multilayered samples, this paper proposes a novel measurement system with a simple structure by using geometric optics. The key point of the overall structure is that the binary linear equation relation between the upper and lower planes of the layer can be known by the distances between laser spots reflected from the layer. Using two optical paths with different incident angles of laser beams, the CCD sensors capture the spot signal for image processing binarization and data sampling. After the obtained laser spots' spacing is substituted into the equations, the thicknesses and refractive indexes of the multilayered samples can be calculated and measured. The proposed measurement system is characterized numerically using simulations on the commercial software program Zemax and then experimentally tested using a laboratory-built prototype. The experiment results show that the refractive indexes and the thicknesses of three-layer samples were measured with high accuracy (with maximum measurement errors of 2.4% and 2% for a refractive index n and thickness t, respectively).

The strapdown inertial navigation system is generally used for photoelectric target calibration. The inertial navigation axis should be characterized by the photoelectric auto-collimation system for the measurement of the equipment axis. The consistency between the axis characterized by the photoelectric auto-collimation system and the inertial navigation axis is an important factor affecting the target calibration accuracy. In order to improve the measurement accuracy and efficiency of the photoelectric target calibration system, a photoelectric characterization and calibration method of the inertial navigation axis was proposed. This method was based on the analysis of the relationship between the deviation and consistency of the measurement results, and the angle deviation value between the auto-collimation system optical axis and the inertial navigation axis was obtained by fitting the experimental data, which was used for the system correction, so as to realize the high-precision calibration. Through the test, by combining the traditional optical machine correction method with the photoelectric calibration method, the calibration efficiency of the system could be greatly improved, and the consistency accuracy between the inertial navigation axis and the optical axis was less than 15″ at the same time. The experimental results show that compared with the traditional optical machine correction method by the traditional optical flat-crystal, the proposed method has higher characterization accuracy and calibration accuracy, which is suitable for high-precision inertial measurement system.

The electrical properties of materials and their dependence on frequency and temperature are indispensable in designing electromagnetic devices and systems in various areas of engineering and science for both basic and applied researches. A free-space transmission/reflection method measuring the free-space scattering parameters of a material under test (MUT) located at the middle of transmit/receive antennas in a free space is suitable for non-destructively testing the MUT without prior machining or physical contact in high-frequency range. This paper describes a planar offset short applicable to the calibration of a quasi-optic based free-space material measurement system in the millimeter-wave frequency range. The measurement results of the dimensional and electrical properties for the three fabricated planar offset shorts with the phase difference of 120° between the reflection coefficients of the planar shorts in the W-band (75–110 GHz) are presented.

The 7-hole probe measurement system is mainly used to measure three-dimensional flow fields. During the measurement, the probe head was in direct contact with the measured object, and the head structure had a significant influence on the accuracy of the flow field measurement. The main influencing factors were the hole opening mode, hole position, and hole diameter. For a hemispherical 7-hole probe with perpendicular and forward-facing holes, orthogonal experiments with three levels and three factors (inflow velocity, hole position, and hole diameter) were designed, and additional experiments were conducted on the significant factors. The importance of factors was evaluated based on the correlation between different structural parameters and the pressure coefficient. The experiment was simulated using FLUENT, and the numerical simulation results demonstrated that the square of deviance at the inlet velocity, hole diameter, and hole position was 0.0018, 0.0013, and 0.3611, respectively. The position of the hole has a significant influence on the measurement results, but the influence of the inflow velocity and hole diameter is negligible, and the pressure coefficient is the smallest when the hole is at 45°. For the hemispherical 7-hole probe with forward facing hole, the hole is the best at approximately 45°, and considering the convenience of processing, the diameter of the hole can be selected as the diameter of the 1/10 probe.

In this work, we propose a real-time noncontact thickness measurement system for conductive materials based on an inductor–capacitor ( LC ) resonant eddy-current sensor. For the aluminum, copper, stainless steel 304, and carbon steel samples of various thicknesses, the in-phase and quadrature components of the sensor output taken during liftoff scans are found to be a series of quadratic-like curves on the phase versus logarithmic amplitude diagram. These curves can be used to generate the standard phase–amplitude relations for thickness conversion. The phase–amplitude relations of the thickness between the values of standard samples are calculated by cubic spline interpolation. With the standard database of phase–amplitude relations, the noncontact thickness measurement was implemented in real time for the copper foil sample with an error of ±3% when the liftoff distance is less than 5 mm. The liftoff tolerance is as large as 100% of the probe diameter, indicating that the proposed method is useful for online quality inspection of conductor films on flexible substrates.

Deflectometry is a promising method for the in situ measurement of specular surfaces. However, the accuracy of this method largely depends on the geometrical calibration, which suffers from a low convergence rate and local minima during the optimization. Off-machine calibration results in a change in geometry parameters due to the repeated disassembly of the measurement system and change of ambient temperature, which largely affects the measurement accuracy. This article presents a flexible on-machine calibration method with fewer intermediate parameters to accelerate the optimization for the in situ stereo deflectometry system. An inclined mirror with a fixed angle was mounted on the spindle of an ultraprecision machine tool and used as a reference plane reflecting the fringe displayed on the display screen. The reflected fringe captured by the cameras was encoded by an inclined mirror moving along the $C$ -axis and the $Z$ -axis of the machine tool. The preknowledge of the movement distance of the ultraprecision machine tool along the $Z$ -axis and rotation angle of the spindle with a nanoscale accuracy was used to largely reduce the number of intermediate variables involved in the optimization, thus improving the convergence speed of the global optimization method and calibration reliability. The experiment results show that this calibration method has higher calibration accuracy, measurement accuracy, and reliability compared to the conventional off-machine calibration method.

In a temperature-controlled radio frequency (RF) power measurement system, there is a temperature difference between the system and the environment temperature. If a metal waveguide is used in the system, heat can reach the core of the system and affect the measurement. An adiabatic waveguide is utilized to reduce this heat flow. This article introduces several WR10 rectangular waveguides that are used in the Korea Research Institute of Standards and Science (KRISS) microcalorimeter and an evaluation system that can measure the adiabatic performance of the waveguides via a thermostat. The basic concept and measurement setup for the evaluation system are briefly introduced, and the structure and the function of the waveguide heat source and heat sense modules of the thermostat are presented. The test results of the adiabatic performance of several WR10 rectangular waveguides are compared and the electromagnetic performance is presented. We also tested preliminary dielectric waveguides that have been co-studied with Physikalisch-Technische Bundesanstalt (PTB), Germany recently. We propose an index to characterize the adiabatic performance of the waveguides. Based on the index results, we improve the adiabatic performance of our newly electroforming-processed adiabatic waveguide with a thick resin coating, which is forty times higher than that of the prototype KRISS microcalorimeter adiabatic waveguide. Finally, we fabricated and investigated dielectric waveguides that have a superb adiabatic property for the microcalorimeter application.

The pinhole runner is the key component of the optical-path automatic calibration system of an experimental device, and the repeated positioning accuracy is one of its important indexes. In order to effectively measure the repeated positioning accuracy of the pinhole runner in vacuum environment, a measurement method based on the combination of laser and charge coupled device (CCD) was proposed, and the position repeatability of laser spot center of runner filtering pinhole was taken as the evaluation index of its repeated positioning accuracy. A complete set of measurement system was built, the laser spot filtered through the runner filtering pinhole was collected by CCD, and the laser spot image was preprocessed by the image processing methods, such as filtering and noise reduction, threshold segmentation, binarization and edge detection. The least square method was used for circle fitting of the laser spot, and the center coordinates of laser spot were obtained. Compared with laser interferometer in non- vacuum environment, the angular deviation between them was only 11″, which showed that the measurement method had high accuracy and met the measurement requirements. Finally, the repeatability measurement of the pinhole runner in vacuum environment was carried out for about 60 times forward and backward reciprocation in about 6 hours. The results show that the method can effectively measure the repeated positioning accuracy of the pinhole runner in vacuum environment.

The article discusses the noise, dynamic and accuracy parameters of acousto-optical (AO) laser measuring systems (LMS) for high-precision control of three-coordinate (3D) displacements of products. It is shown that now when using modern high-speed low-noise photodetectors makes it possible to achieve the resolution of AO LMS without special technical techniques for longitudinal Δlx and transverse Δly , Δlz displacements, respectively, where λ and Λaom are the wavelength of light and sound in the AO modulator. The features of using PLL systems in AO LMS are discussed. The possibilities of increasing the resolution when measuring displacements using two photodetectors for one input optical signal: high-speed and low-noise, as well as by controlling the bandwidth of the PLL system are considered.

In this article, we proposed a measurement system that can simultaneously measure temperature and pressure. By analyzing several existing measurement methods of the sensor, we determined that the resonance frequency and $S_{11}$ (reflection coefficient) amplitude of the sensor readout system should be measured when the resonance frequency of the sensor up to a hundred megahertz or even gigahertz and when the sensor works in ultrahigh temperature environment. In addition, we designed a simple and accurate sensor readout circuit and an LC temperature–pressure sensor. By analyzing the resonance frequency and the amplitude of $S_{11}$ , temperature and pressure were measured simultaneously with a single LC circuit. Since the analysis of the whole nonlinear system of sensors is complex, we divide the entire nonlinear system into several linear systems superposition. By analyzing the interference between temperature and pressure, we further optimized the measurement method. The relative errors of the temperature measurements in the range of 25 °C–300 °C and 300 °C–1000 °C were only 2.89% and 1.25%, respectively. From 25 °C to 300 °C and 300 °C to 1000 °C, the average relative errors of pressure measurement were only 4.07% and 4.74%, respectively. Besides, the proposed method can also be widely used in the measurement of LC multiparameter sensors.

Microdisplacement detection plays a vital role in the position diagnosis and accurate calibration of micro-electro-mechanical systems (MEMS) actuators. An optical microdisplacement detector proposed in this article integrated a vertical cavity surface-emitting laser and nine photodiodes (PDs) to detect the submicrometer translation and subdegree rotation of the piezoelectric microvibratory stage under the limited space. The highly accurate detection was mainly realized by PDs design and quality improvement. Nine PDs layout with high-resolution optical sensors and corresponding calculation guaranteed the detector to precisely acquire out-of-plane displacement and two-axis rotation of the vibratory platform. And the introduction of the light-absorbing layer and the light-shielding layer further improved the sensing quality to reach a higher measurement resolution. The microstage was fabricated by MEMS technology and the experiments of measurement system indicated that the out-of-plane displacement detection accuracy was 150 nm in the range of 500 μ m and the angle detection accuracy reached 0.1° in the range of 2°.

In-plane retardation and out-of-plane retardation by optically anisotropic medium are generally measured with the Mueller polarimeter. We proposed a method for measuring the in-plane retardation and out-of-plane retardation using the Stokes polarimeter. The suggested method requires no polarization state generator, simplifying the measurement system. The retardation measured with the Stokes polarimeter was compared with the data measured with the Mueller polarimeter, and their difference was less than 2.5 nm ( $0.005\lambda$ ). In addition, the suggested method can find the orientation of the slow axis of the retarder and the order of retardation. Although the conventional methods require measurements at multiple wavelengths to distinguish the order of the retardation, the suggested method can find the exact retardation using data at a single wavelength of light.

Aiming at the problems of Doppler-induced error and slow measurement rate in frequency-swept interferometry, a novel dynamic clearance measuring method is proposed. By combining frequency-swept and frequency-fixed interferometry, and using fusion processing of interferometric signals, this method not only can eliminate the Doppler-induced error, but also can give the dynamic clearance value at each sampling point. To verify this method, an all fiber-optic measurement system was constructed, and experiments under 500 Hz triangular and 4 kHz sinusoidal vibrations were carried out. Experimental results show that the dynamic clearance can be reconstructed accurately.

A new stretched-wire system is built for a cryogenic permanent magnet undulator in High Energy Photon Source Testing Facility. The system has two functions: integral field measurement and magnet gap measurement. Integral field measurement and gap measurement are important for evaluation and optimization of the magnetic performance of the undulator in cryogenic–vacuum environment. Two high-precision, high-load motion stages are used for accurate positioning. A special fix structure of stretched wire is adopted for vacuum environment. To reduce the deflection of the 3-meter-long wire, constant tension is maintained along the wire. The measurement repeatability of field integral and magnetic gap is the key performance which depends on the stability of wire and suppression of the electric noise. Strategy of improving the measurement accuracy and stability is presented.

A measurement system for nondestructive electromagnetic characterization of two-layer absorbers made of a dielectric layer on top of a lossy magnetic layer is presented. The characterization includes simultaneous determination of the complex permittivity of the first layer and the complex permittivity and permeability of the second layer over a broad frequency bandwidth. The measurement system is composed of two flanged open-ended coaxial probes coupled to each other via a two-layer absorber. A full-wave analytical model is worked out to determine the theoretical reflection and transmission coefficients. The material properties of each layer are extracted by solving the inverse problem via nonlinear least squares. Numerical and experimental results for a two-layer absorber are reported and compared with those of standard 7 mm coaxial measurements to validate the proposed approach.

Scintillator Neutron Detectors Arrays (SNDA) were successfully installed at General Purpose Powder Diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The inhomogeneity of the detection efficiency in each detector module, which caused by the gain nonuniformity of the multi-anode photo-multiplier tubes (MA-PMTs) and the inconsistency of the wave-length shifting fibers in collecting scintillation photons, need to be mitigated before the installation. An automated rapid measurement system based on the blue laser and the two-dimensional mobile platform was developed to calibrate the light response of each channel in detector modules. According to the test results of this system, the electronics threshold of each channel of the SNDA is adjusted. Before the installation of the all 40 SNDA modules in GPPD, the electronics thresholds of each channel are adjusted according to the measurement results of this rapid measurement system. Compared with the unadjusted detector module, the adjusted one obtained a better uniformity of the neutron detection efficiency. The inhomogeneity of the detection efficiency is improved from 27.4% to 10.9%. The test result of the diffraction peak of the standard sample Si showed that the adjusted SNDA works well in GPPD.

A real-time free spectral range (FSR) measurement system based on heterodyne optical phase-locked loop (HOPLL) is proposed for the first time to test the FSR of a fiber resonator. In this system, HOPLL is used to lock phase between the master and slave lasers, so that the frequency difference between them reach one FSR. In addition, PDH technique is used to establish a resonant tracking loop. By setting the loop control parameters, the master and slave lasers are respectively locked on two adjacent resonance peaks of the cavity. If the ambient temperature changes, the cavity length of the resonant cavity will change accordingly. Then the real-time change of FSR of the resonant cavity can be measured by detecting feedback change of the loop. The experimental results show that the linewidth of beat signal of the master and slave lasers after phase-locking is less than 10Hz, and also the frequency noise of the 10Hz bandwidth is 0.0154Hz which is 60dB lower than that before phase-locking. The researchers find that the FSR coefficient of thermal expansion is −210.35 ± 0.15Hz/°C, which is consistent with theoretical results. The relative measurement accuracy of $1.5\times 10 ^{-9}$ is achieved in this loop. Therefore, the experimental results effectively verify the actual application performance of the real-time FSR measurement based on HOPLL technique.

A broadband measurement technique for the normal-incidence absorptivity based on parallel-plate waveguide (PPW) is proposed. The method is well suited for frequency-selective surface (FSS)-based absorbers. By employing the PPW structure, only a small sample size, i.e., 1-D array of FSS, is required for the measurement. The thru-reflect-line (TRL) calibration is implemented to remove the time-gating ambiguity in the conventional PPW-based method. A measurement system working up to 6 GHz is designed such that its length is adjustable to ensure all three calibration standards (thru, reflect, and line) can be carried out in a single device. Moreover, the height of the PPW is also adjustable to allow the measurement of absorbers with a different periodicity of FSSs. Two single-layer FSS-based absorbers with different periodicity are fabricated and measured. The results agree well with the conventional free-space measurement system, which validates the proposed method.

Measuring systems using the design of laser module beams on the surface of the object under study are considered. A technique is proposed for experimental studies of the brightness structure of the study of laser modules for their subsequent testing. Adaptive algorithms for determining the type of module and distance have been developed for determining the coordinates of light marks on the surface of controlled products, ensuring the accuracy and reliability of the measurement. The need for high-precision measuring systems to carry out their preliminary selection and calibration of laser modules according to the proposed method, taking into account the range of design of light marks, is shown. It is shown in the work that the accuracy of determining the relative coordinates in the trajectory of the light marks of laser modules at a distance of 5 m for plain surfaces of the observed objects can be several times higher (0,2…0,3 mm) of the accuracy of determining their absolute coordinates (»1 mm).

The article presents the results of the development of a system for measuring emittance characteristics of ion sources studied at the IAP NAS of Ukraine with the aim of obtaining the ion beams with a high brightness. The emittance measurement system is based on the scheme of an electrostatic scanner and consists of two main parts: the scanner, which moves in the direction perpendicular to the beam axis using a stepper motor, and the electronic system of control, processing and data acquisition. The electronic system contains a Raspberry pi 3B microcomputer, precision DAC/ADCs, the high-voltage amplifier of a scanning voltage up to ±500 V on deflection plates of the scanner and a wide range current integrator. The determination of the emittance consists in measuring the ion beam intensity distribution when the scanner moves along the x-coordinate and the electrostatic scanning along the x´ angle. The obtained two-dimensional data array allows determining the main characteristics of ion beam: geometric 90% emittance, the root mean square (rms) emittance, the Twiss parameters and phase ellipse of rms emittance, the beam current profile and the angle current density distribution. To test the performance and functionality of the system, the emittance characteristics of the penning type ion source were measured. The working gas was helium, and the beam energy varied within 7–15 keV. At 13 keV of beam energy the following emittances of the He+ ions beam was obtained: 90% emittance is 30 π∙mm∙mrad, rms emittance is 8.4 mm∙mrad, and the normalized rms emittance is equal to 0.022 mm∙mrad. The developed system for measuring the emittance of the ion beams is characterized by a short measurement time of 10-15 minutes.

Data on the waviness of a processed part related to the coordinate system associated with the laser treatment bench used with a surface are needed to increase the effectiveness of the technology of laser destructuring. At the present time, there are no contactless topographic measurement instruments that meet all the requirements that are imposed on the system used in measurement of the profile of the surface of parts and that are determined by the parameters of the technological process of laser destructuring. A trial design of a system for measurement of the profile of a surface (waviness) constructed according to the principle of an optical profilometer and modified in accordance with the requirements imposed on measurements performed on a laser treatment bench is created. Through the use of the system measurements of waviness are performed directly on the bench, which significantly reduces the length and difficulty of the technological process. A diagram and operating principle of the waviness measurement system on a laser destructing bench are described. A triangulation method is used in the measurements. Through the use of a trial design of the system the waviness profi le of a surface with spatial wavelength 2 mm may be measured with error 3.78 μm in the vertical direction and 13.8 μm in the lateral direction. Verification of the precision of the trial design of the system is performed by a standard method of stylus profilometry. The waviness profile of a surface obtained with the use of the trial design of the system may be used for modulation of the amplitude of the power of laser radiation in hte technological process of laser destructuring.

In the ultra-precision manufacturing of large optics, industrial robots have the potential to become an intelligent and economical choice of surface polishing. However, the transport of the workpieces between the polishing platform and the measurement instrument seriously limits the manufacturing efficiency. Therefore, an in-situ measurement system based on the monoscopic deflectometry is developed to determine the form quality of the optical lenses during rough polishing. Stray light reflected from the lower surface of transparent lenses may degrade the measuring quality, thus an effective absolute phase retrieval algorithm is developed to decouple the superposed fringes associated with the upper and lower surfaces. Then, the form of the upper surface under polishing can be reconstructed to guide the subsequent polishing. Experimental results demonstrate that the accuracy of the method is comparable to that of the coordinate measuring machine, consequently the manufacturing efficiency and reliability of large optical workpieces can be greatly improved.