Metrology Techniques Research Articles

Single-shot high speed aerial chromatic confocal metrology sensor

Chromatic confocal metrology is a widely established optical metrology technique, which allows for noncontact, high-speed three-dimensional surface profiling without the need of mechanical depth scanning. However, current methods are limited by the use of some sort of surface scanning method with mechanically moving parts. Furthermore, the setups involve a spectrometer setup, either through prisms, gratings, or multispectral cameras. This drastically limits the simultaneously measureable positions in lateral direction, as the spectrometer setup will utilize one spatial dimension for the wavelength domain. We present a method for chromatic confocal metrology that enables high-speed and high-resolution one-shot aerial surface metrology. This method is scalable with respect to measurement range in axial as well as in lateral direction and in the number of measurement points that can be measured simultaneously. After deriving the theoretical basis of the approach, a virtual optical design with a field of view of 10 mm × 10 mm and a depth range of 1.5 mm with roughly 1000 measurement points, based mainly on off-the-shelf components will be presented. This virtual system design was used to perform various simulations and explain the design process and considerations as well as the expected system response of the proposed system.

Photon force microelectromechanical system cantilever combined with a fibre optic system as a measurement technique for optomechanical studies

In this paper we present a metrological measurement technique that is a combination of fibre optic interferometry and a microelectromechanical system (MEMS) sensor for photon force (PF) measurement with traceability via an electromagnetic method. The main advantage of the presented method is the reference to the current balance, which is the primary mass/force metrological standard. The MEMS cantilever transduces the PF to a deflection that can be compensated with the use of the Lorentz force. This movement is measured with the use of the interferometer and does not require any mechanical calibration. Combining the MEMS current balance system with interferometry is a unique and fully metrological solution. The resolution of the proposed measurement technique is calculated to be 4 pN Hz–0.5 (2% uncertainty). The PF–MEMS used for the investigation is a cantilever with a resolution of 46 fN Hz–0.5, which was calculated from the thermomechanical noise and is far below the resolution limit of the whole system. Because the whole construction is based on a fibre optic system, it does not require any complex adjustment procedure and may work as an optomechanical reference in any metrological laboratory.

Evaluating Rail Surface Roughness from Axle-Box Acceleration Measurements: Computational Metrology Approach

This study develops a new methodology based on computational metrology techniques to measure rail surface roughness from vertical axle-box accelerations. A VIA rail passenger rail car, operating in eastern Ontario, Canada, was instrumented with accelerometers on the car body, trucks, and axle-boxes. The rail surface was measured by a heavy track geometry inspection car. A Gaussian filter was applied to the measured rail surface data and the rail surface roughness was quantified by the root mean square (RMS), as recommended by ISO 11562 for evaluating engineering surfaces. Values of rail surface RMS roughness calculated from axle-box accelerometer data are verified with the measured surface RMS roughness. The overlap ratio and length of the moving window over which the rail surface RMS roughness is calculated are studied with respect to roughness wavelengths, statistical considerations, and maintenance planning purposes. The effect of rail car operating speed as well as the difference between axle-box accelerations measured at two axles of the instrumented rail car on the accuracy of estimating the rail surface RMS roughness are assessed. Filtering techniques and application limitations for calculating roughness are also discussed. The results of this study suggest axle-box acceleration data provide a useful assessment of rail surface roughness for the typical wavelengths between 3 and 25 m and a complementary technique to light and heavy track geometry inspections.

A Review of Lithium‐Ion Battery Electrode Drying: Mechanisms and Metrology

AbstractLithium‐ion battery manufacturing chain is extremely complex with many controllable parameters especially for the drying process. These processes affect the porous structure and properties of these electrode films and influence the final cell performance properties. However, there is limited available drying information and the dynamics are poorly understood due to the limitation of the existing metrology. There is an emerging need to develop new methodologies to understand the drying dynamics to achieve improved quality control of the electrode coatings. A comprehensive summary of the parameters and variables relevant to the wet electrode film drying process is presented, and its consequences/effects on the finished electrode/final cell properties are mapped. The development of the drying mechanism is critically discussed according to existing modeling studies. Then, the existing and potential metrology techniques, either in situ or ex situ in the drying process are reviewed. This work is intended to develop new perspectives on the application of advanced techniques to enable a more predictive approach to identify optimum lithium‐ion battery manufacturing conditions, with a focus upon the critical drying process.

Simultaneous Dimensional and Analytical Characterization of Ordered Nanostructures.

The spatial and compositional complexity of 3D structures employed in today's nanotechnologies has developed to a level at which the requirements for process development and control can no longer fully be met by existing metrology techniques. For instance, buried parts in stratified nanostructures, which are often crucial for device functionality, can only be probed in a destructive manner in few locations as many existing nondestructive techniques only probe the objects surfaces. Here, it is demonstrated that grazing exit X-ray fluorescence can simultaneously characterize an ensemble of regularly ordered nanostructures simultaneously with respect to their dimensional properties and their elemental composition. This technique is nondestructive and compatible to typically sized test fields, allowing the same array of structures to be studied by other techniques. For crucial parameters, the technique provides sub-nm discrimination capabilities and it does not require access-limited large-scale research facilities as it is compatible to laboratory-scaleinstrumentation.

Camera calibration method using synthetic speckle pattern with an improved gray wolf optimizer algorithm.

Camera calibration is essential for various vision-based 3D metrological techniques. In this paper, a novel camera calibration method, to the best of our knowledge, combining synthetic speckle pattern and an improved gray wolf optimizer algorithm is presented. The synthetic speckle pattern serves as the calibration target. The particle swarm algorithm-based digital image correlation is employed to achieve matches among 3D control points and 2D image points; then the improved gray wolf optimizer algorithm is used to calculate the camera parameters. For verification, simulated and real tests are conducted. Through the analysis of calibration results, the proposed method performs better and is more stable than other calibration targets. Research on the influence of camera pose and optimization algorithm is conducted, showing that the improved gray wolf optimizer algorithm performs better than other benchmark algorithms. The camera parameters can be obtained through one captured image when the speckle patterns are added in the portion of the camera sensor.

Optimal circular dichroism sensing with quantum light: Multiparameter estimation approach

The measurement of circular dichroism (CD) has widely been exploited to distinguish the different enantiomers of chiral structures. It has been applied to natural materials (e.g. molecules) as well as to artificial materials (e.g. nanophotonic structures). However, especially for chiral molecules the signal level is very low and increasing the signal-to-noise ratio is of paramount importance to either shorten the necessary measurement time or to lower the minimum detectable molecule concentration. As one solution to this problem, we propose here to use quantum states of light in CD sensing to reduce the noise below the shot noise limit that is encountered when using coherent states of light. Through a multi-parameter estimation approach, we identify the ultimate quantum limit to precision of CD sensing, allowing for general schemes including additional ancillary modes. We show that the ultimate quantum limit can be achieved by various optimal schemes. It includes not only Fock state input in direct sensing configuration but also twin-beam input in ancilla-assisted sensing configuration, for both of which photon number resolving detection needs to be performed as the optimal measurement setting. These optimal schemes offer a significant quantum enhancement even in the presence of additional system loss. The optimality of a practical scheme using a twin-beam state in direct sensing configuration is also investigated in details as a nearly optimal scheme for CD sensing when the actual CD signal is very small. Alternative schemes involving single-photon sources and detectors are also proposed. This work paves the way for further investigations of quantum metrological techniques in chirality sensing.

Carrier fringe pattern analysis: Links between methods

Introducing a carrier into a fringe pattern makes the phase retrieval problem well-posed, and has become one of the pillar techniques in optical metrology. The carrier fringe pattern analysis for high-accuracy phase retrieval is hence important, for which, many well-known methods have been developed, such as the Fourier transform method, the windowed Fourier transform based methods (the windowed Fourier filtering and the windowed Fourier ridges), the spatial carrier phase-shifting method, and the sampling moiré method. These methods were developed independently and seemingly different. The purpose of this paper is to reveal the close relationships between them, and to connect these methods into a tight-knit methodology family.

Optical superoscillation technologies beyond the diffraction limit

Optical superoscillations are rapid, subwavelength spatial variations of the intensity and phase of light, occurring in complex electromagnetic fields formed by the interference of several coherent waves. The discovery of superoscillations stimulated a revision of the limits of classical electromagnetism — in particular, the studies of phenomena such as unlimitedly small energy hotspots, phase singularities, energy backflow, anomalously high wavevectors and their intriguing similarities to the evanescent plasmonic fields on metals. In recent years, the understanding of superoscillatory light has led to the development of superoscillatory lensing, imaging and metrology technologies. Dielectric, metallic and metamaterial nanostructured superoscillatory lenses have been introduced that are able to create hotspots smaller than allowed by conventional lenses. Far-field, label-free, non-intrusive deeply subwavelength super-resolution imaging and metrology techniques that exploit high light localization and rapid variation of phase in superoscillatory fields have also been developed, including new approaches based on artificial intelligence. We review the fundamental properties of superoscillatory optical fields and examine emerging technological applications.

Electron-optical in-situ metrology for electron beam powder bed fusion: calibration and validation

A major advantage of metal additive manufacturing is the possibility for tool-free production of complex shaped parts. Currently, the geometrical and dimensional accuracy of these parts can only be reliably controlled by time and cost intensive post-process inspection, e.g. using x-ray computed tomography (XCT). The current investigation demonstrates the first in-situ metrology technique for electron beam powder bed fusion (PBF-EB) using electron-optical imaging (ELO). After a calibration experiment, the approach was validated for a PBF-EB build job by comparing in-situ ELO imaging data to XCT data of an as-built part. The quantitative comparison showed a remarkable high agreement between both imaging techniques. It is demonstrated that ELO imaging is capable of making accurate predictions on the geometrical and dimensional accuracy of the as-build part. This result is the basis of new possibilities for in-situ process and quality control in PBF-EB.

Moire profilometry through simultaneous dual fringe projection for accurate phase demodulation: a comparative study.

In optical metrology, fringe projection and moire techniques have been widely used to measure the topography of objects. We can combine the advantages of the two techniques by applying a configuration of simultaneous dual projection in the fringe projection technique, which generates a superimposed fringe pattern containing a moire pattern that is phase modulated according to the topography. In this work, we present an analytic and comparative study of three methods to demodulate the phase of the moire pattern: the spatial, spatial-temporal, and temporal methods. Those methods consist of two steps: first, the moire pattern is extracted from the superimposed fringe pattern; next, the phase of the moire pattern is demodulated. The analytical results show that the resulting phase map has double phase sensitivity compared to that of the classical fringe projection technique. Experimental and numeric results prove the feasibility of this technique.

Nano-precision metrology of X-ray mirrors with laser speckle angular measurement

X-ray mirrors are widely used for synchrotron radiation, free-electron lasers, and astronomical telescopes. The short wavelength and grazing incidence impose strict limits on the permissible slope error. Advanced polishing techniques have already produced mirrors with slope errors below 50 nrad root mean square (rms), but existing metrology techniques struggle to measure them. Here, we describe a laser speckle angular measurement (SAM) approach to overcome such limitations. We also demonstrate that the angular precision of slope error measurements can be pushed down to 20nrad rms by utilizing an advanced sub-pixel tracking algorithm. Furthermore, SAM allows the measurement of mirrors in two dimensions with radii of curvature as low as a few hundred millimeters. Importantly, the instrument based on SAM is compact, low-cost, and easy to integrate with most other existing X-ray mirror metrology instruments, such as the long trace profiler (LTP) and nanometer optical metrology (NOM). The proposed nanometrology method represents an important milestone and potentially opens up new possibilities to develop next-generation super-polished X-ray mirrors, which will advance the development of X-ray nanoprobes, coherence preservation, and astronomical physics.

Microscale Thermophoresis in Liquids Induced by Plasmonic Heating and Characterized by Phase and Fluorescence Microscopies

Thermophoresis denotes the motion of particles along temperature gradients. Insignificant in most daily-life observations, this peculiar effect can become dominant in applications involving nano- and microscale heating in fluids. Recent studies in nanoplasmonics observed significant thermophoresis of molecules and particles, in particular in plasmonic trapping, SERS, and biosensing. Evidencing the presence of thermophoresis is not obvious and quantifying its magnitude is even less accessible considering existing techniques. In this article, we introduce a method capable of quantifying the thermophoresis of particles in the context of nanoplasmonic applications. A gold nanoparticle array under illumination is used to create microscale temperature gradients, and a dual fluorescence-phase microscopy technique is used to map both temperature and concentration in parallel. This association enables the determination of Soret coefficients for a wide range of temperatures from a single image acquisition. This metrology technique paves the way for broader fundamental research in microscale thermophoresis in liquids and better-controlled applications in nanophotonics involving thermoplasmonic effects.

Application of the Vernier method with the phase shift time of flight technique for optical metrology

The phase shift (PS) continuous wave time of flight (PS CW TOF) method is an optical measuring technique that can be used to obtain high accuracy absolute and relative distance measurements. Optical systems based on this method can be applied as a simple and low-cost metrology solution for application in an industrial and scientific context.A PS CW TOF range finder determines a source-target distance by comparing the phase difference of a continuously modulated signal in its source and when it is detected. Due to the cyclical properties of the phase angle, the position information is contained within an ambiguity interval. There are several established techniques that can be used to remove the ambiguity in this method, they usually rely in increasing the unambiguous range, using auxiliary measuring techniques or multiple modulation frequencies.In this work, we present a Vernier approach applied to the dual-frequency PS CW TOF method to remove the ambiguity in a phase measurement. We validate the proposed methodology by constructing an experimental setup based on heterodyne down conversion to perform distance measurements in a [0, 5] m range. This technique allowed reaching an expanded uncertainty in the distance measurement of ≈ 530 μm with k = 2 with a modulation frequency of 1.825 GHz.

Biopolymer hydroxyapatite composite materials: Adding fluorescence lifetime imaging microscopy to the characterization toolkit

AbstractBiopolymers are frequently used due to their sourcing from renewable resources, widespread abundance, and cheap procurement costs. When combined with hydroxyapatite (HA), these materials are often used as restorative materials by general and oral health care providers and in veterinary medicine due to their unique properties of mimicking their biological congeners. When designing the next generation of restorative materials, it will be critical to understand the interactions between biopolymers and HA on micron and submicron length scales, which will require expanding the characterization toolkit. Fluorescence microscopy is one powerful tool for investigating materials on these length scales. Fluorescence lifetime imaging microscopy (FLIM), a technique that measures the fluorescence lifetime of fluorophores based on local environments, could be used to observe the structural properties of materials. In this review, FLIM is discussed as an addition to the characterization toolkit for its potential to provide unique insights into biocomposite material structure‐property relationships. Additional topics include structure‐property processing relationships, imaging and metrology technique advances, and the ability of FLIM to complement these techniques. Overall, this review complements the literature by providing a new methodology to uncover previously unknown information through microscopy.

Design and validation of a prototype to calibrate the pressure variable in tonometry

This paper corresponds to the results of an experimental research that to led to the design of a useful prototype for quality control of measurements in the field of tonometry to diagnose and check glaucoma. All tonometry techniques are based on Goldmann ́s tonometers (GT) and the Imbert-Fick principle. Taking into account the principles and techniques of industrial metrology, the prototype could be used as a standard to calibrate the pressure readings of this class of tonometers. The developed protoype eliminates the indirect measurement that is required with current standards and facilitates a greater control of the sources of error in the measurement. The model is based on the integration of a sensor to a hydraulic model to measure pressures from 0 to 80 mmHg range, whose precision was validated through R&R studies. The precision of the prototype was validated according to the Rigel UNI-SIM standard and was complemented by calibrating 15 tonometers.

The combined use of wrinkling and cracking for the characterization of the mechanical properties of the laser-fabricated nanometer-thick amorphous carbon films

Direct laser writing carbonization has been recently developed to enable facile fabrication of patternable nanometer-thick two-dimensional amorphous carbon films, which may find promising applications in high-performance sensing, energy storage, catalysis, biomaterials etc. Given its nanometer-thick character and brittleness in nature, it is quite challenging to evaluate and characterize the mechanical properties of this novel material. With assistance of a sacrificial-layer transfer approach for sample preparation, herein, we rely on wrinkling metrology as a viable tool for characterizing the elastic modulus of the laser-fabricated nanometer thick amorphous carbon films. Moreover, upon combining the wrinkling metrology with channel cracking behavior investigation, the strength-related mechanical properties, including fracture toughness, fracture strength and fracture strain of the carbon thin films of varied thickness have been evaluated comprehensively. Within the experimental conditions being studied, the elastic modulus, fracture toughness, fracture strength and fracture strain of the laser-fabricated nanometer-thick carbon films respectively fall in a range of 23.1–34.9 GPa, 16.3–151.7 J/m2, 0.5–1.4 GPa, and 2.0–4.5%. The results and methodology presented in this study demonstrate the usefulness of combining wrinkling metrology and cracking technique as a simple but generally applicable approach for comprehensive characterization and evaluation of the mechanical properties of different types of brittle and nanometer-thick thin films.

Transfer phase of microwave to beat amplitude in a Rydberg atom-based mixer by Zeeman modulation

Microwave phase detection is an essential technique in antenna metrology, radar, and communications. The Rydberg atom-based mixer has been successful in the measurement of the phase of a signal microwave field by creating a beat in the presence of a local microwave field, in which the phase information is transferred into the phase of the beat. In this study, we extend the function of the Rydberg atom-based mixer by adding alternating current Zeeman modulation, and find that the phase information is transferred into the amplitude of the beat, not only its phase. As the results, the phase information can be measured simply and real-time. The results show that another ‘dimension’ operation can be introduced into the Rydberg atom-based mixer to expand the functions and applications of the mixer, which is very useful for future real-time sensing applications. An experiment involving real-time measurement and phase-modulated digital communication based on the beat+Zeeman method is presented.

Review Article] Recent Techniques in Surface Metrology

Review Article] Recent Techniques in Surface Metrology

Silicon Micromachined Waveguide Calibration Standards for Terahertz Metrology

This article presents precision silicon micromachined waveguide calibration standards for use with terahertz vector network analyzers. This enables the creation of precise, highly repeatable, and traceable terahertz waveguide standards, surpassing the limits of current metrology techniques. A single silicon-on-insulator wafer with the appropriate device and handle layer thicknesses is used to implement a wide range of calibration and verification standards. The design of the standards is discussed from mechanical, electrical, and end-user perspectives. Silicon is shown to be the most promising material for the realization of precision metrology standards. We outline the potential to scale the presented design to at least 2.6 THz. Eight types of WM-570 standard, totaling 15 prototypes, are fabricated and characterized between 325 and 500 GHz. Despite some fabrication anomalies, all devices offer excellent performance. The best micromachined standards offer a return loss in excess of 40 dB, an insertion loss of below 0.1 dB, and a phase error of less than 1°. The standards are utilized in both one- and two-port calibrations, including the multiline through-reflect-line algorithm. These are benchmarked against calibrations performed using conventional metallic standards, with a high degree of agreement observed between error-corrected measurements of a range of test devices.