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- 摘要
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- 实验方案
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A study of a priori knowledge-assisted multi-scopic metrology for freeform surface measurement
摘要： The traditional multi-scopic metrology system makes use of a micro lens array to capture a raw 3D-image of the target surface in a single snapshot through a CCD camera under normal illumination. However, the resolution of the system depends on the matching precision and efficiency of disparity information during the processing of the 3D raw data. In this paper, the a priori knowledge-assisted multi-scopic metrology is studied and an a priori knowledge-assisted multi-scopic metrology system is established which makes use of patterned illumination custom-designed based on the a priori knowledge of the target freeform surface profile. The a priori knowledge provides abundant versatile known information for a precise and efficient matching process so as to enhance the measuring performance. A customized disparity matching process based on the a priori knowledge is developed accordingly for high-resolution 3D surface reconstruction. An experimental study for measuring freeform surface is conducted to verify the feasibility of the proposed a priori knowledge-assisted multi-scopic metrology system through the comparison between that using normal illumination and a priori knowledge-assisted patterned illumination.
关键词： a priori knowledge-assisted,multi-scopic metrology,Precision surface measurement,autostereoscopy,freeform surface
更新于2025-09-12 10:27:22
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Anwendungen eines fasergekoppelten chromatisch konfokalen Sensors in Nanopositionier- und Nanomessmaschinen / Applications of a fiber coupled chromatic confocal sensor in nanopositioning and nanomeasuring machines
摘要： By developing a new sensor system based on the chromatic confocal principle, the application potential for nano-coordinate measuring machines has expanded [8]. Using the Nanopositioning and Nanomeasuring Machines (NPMM) developed at the Institute for Process Measurement and Sensor Technology (IPMS) at Technische Universit?t Ilmenau, large and precisely addressable and positionable measuring and working volumes are available [9]. The integration of the new sensor into the NPMM and the extension of the system by a lithography laser for maskless Direct-Laser-Writing (DLW) are described [16]. The metrological properties of the sensor are presented and its possible applications in lithographic structuring processes are discussed. The sensor is used to focus the processing laser consistently on the sample surface in the area of its depth of field. This leads to a decrease in the structure widths [17].
关键词： chromatic confocal sensor,Nano-coordinate measuring machines,optical metrology
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Iodine-Stabilized 633 nm Diode Lasers for Metrology and Interferometry
摘要： Helium-neon lasers at 633 nm are still widely used in interferometers and, stabilized to iodine, serve as secondary frequency standards for the practical realisation of the meter [1]. However, the technical know-how for building and maintaining helium-neon laser tubes is slowly disappearing. Diode lasers are an attractive alternative with respect to availability, cost, output power, size and power consumption. The emission wavelength of 633 nm allows new systems to be easily integrated into existing setups. For replacing the helium-neon laser and enhancing the stability and accuracy, we have investigated an extended-cavity diode laser (ECDL) stabilized on an external cavity containing an iodine cell using Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy (NICE-OHMS) at 633 nm. The cavity provides a well-defined, long-term stable geometry, resulting in a robust system. In addition, the increased intra-cavity power and the increased effective absorption length result in absorption signals with high signal-to-noise ratio [2]. NICE-OHMS has been widely used for ultra-sensitive detection of molecular absorption lines [3]. However, for laser stabilization it has only been applied in the infrared regime so far [4,5]. Fig. 1 shows the Allan deviations of a diode laser stabilized to iodine using NICE-OHMS (red) compared to a PTB iodine-stabilized helium-neon laser (black). The diode laser reaches a frequency instability of 3.2(cid:117)10-12 at 1 s, which is lower than for the helium-neon laser (4.1(cid:117)10-12 at 1 s), while the instability of the diode laser starts to rise at averaging times longer than 100 s. Using a NICE-OHMS stabilized diode laser at 633 nm, we have – to the best of our knowledge – reached for the first time a short time frequency instability below that of a state-of-the-art iodine stabilized helium-neon laser. This system has good prospects to serve as a frequency standard at 633 nm. To reach this goal, further investigations of the long-term instability, of the reproducibility and of the sensitivities of the absolute frequency on various parameters are underway.
关键词： Interferometry,Iodine-Stabilized,Metrology,633 nm Diode Lasers,NICE-OHMS
更新于2025-09-12 10:27:22
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Spatial squeezing in bright twin beams generated with four-wave mixing: Constraints on characterization with an electron-multiplying charge-coupled-device camera
摘要： The observation of spatial quantum noise reduction, or spatial squeezing, with a large number of photons can lead to a significant advantage in quantum imaging and quantum metrology due to the scaling of the signal-to-noise ratio with the number of photons. Here we present a systematic study of the limiting factors that play a role on the measurement of spatial squeezing with an electron-multiplying charge-coupled device (EMCCD) camera in the limit of bright quantum states of light generated with a four-wave mixing process in an atomic vapor cell. We detect a total number of photons per beam of the order 108 in 1 μs pulses, which corresponds to a photon flux per beam of the order of 1014 photons per second. We then investigate the role of different parameters, such as cell temperature, pump power, laser detunings, scattered pump background noise, and timing sequences for the image acquisition with the EMCCD camera, on the level of spatial squeezing. We identify critical parameters to obtain an optimum squeezing level and demonstrate that for bright beams it is essential to acquire images at a rate fast enough to overcome the effect of classical technical noise.
关键词： spatial squeezing,atomic vapor cell,quantum imaging,spatial quantum noise reduction,quantum metrology,four-wave mixing,EMCCD camera
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE 5th International Workshop on Metrology for AeroSpace (MetroAeroSpace) - Torino, Italy (2019.6.19-2019.6.21)] 2019 IEEE 5th International Workshop on Metrology for AeroSpace (MetroAeroSpace) - A Novel Demodulation Method Based on Partial Period Curve-fitting for FM Signal in Impact Acceleration Calibration by Using Laser Interference Methods
摘要： Aiming at the digital demodulation problem of FM signals in acceleration calibration by laser interference, a demodulation method based on partial periodic sine wave fitting is proposed. By using a sine wave model with about 1/5 cycles, FM demodulation is realized. It has good adaptability to the laser Doppler impulse signal waveform, and can perform operations without signal interception, and has good algorithm stability and one sampling interval resolution. Experiments on a set of actual measured waveforms verify the correctness and feasibility of the algorithm, and provide an effective method for impact acceleration calibration. The method herein can also be used for demodulation of heterodyne laser interference vibration signals.
关键词： frequency modulation,demodulation,Metrology,impact acceleration,calibration
更新于2025-09-11 14:15:04
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Flash spectral imaging for optical metrology of solar cells
摘要： Flash spectral imaging of full area (156 mm by 156 mm) silicon solar wafers and cells is realized in a setup integrating pseudo-monochromatic LEDs over the wavelength range of 370 to 1050 nm and a high-resolution monochrome camera. The captured information allows the computation of sample reflectance as a function of wavelength and coordinates, thereby constituting a spectral reflectance map. The derived values match that obtained from monochromator-based measurements. Optical inspection is then based on the characteristic reflectance of surface features at optimally contrasting wavelengths. The technique reveals otherwise hidden stains and anti-reflection coating (ARC) non-uniformities, and enable more selective visualization of grains in multicrystalline Si wafers. Optical contrast enhancement of metallization significantly improves accuracy of metal detection. The high effective resolution of the monochrome camera also allows fine metallization patterns to be measured. The rapid succession of flash-and-image-capture at each wavelength makes the reported optical metrology technique amenable in photovoltaic manufacturing for solar wafers/cells sorting, monitoring and optimization of processes.
关键词： Flash spectral imaging,monochrome camera,ARC non-uniformities,optical metrology,metallization,reflectance,LEDs,solar cells
更新于2025-09-11 14:15:04
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Optical Fiber Specklegram Sensors for Mechanical Measurements: a Review
摘要： This paper presents a review of FSS technology. The operation principle and main characteristics of specklegram are presented and the applications of FSSs are thoroughly discussed. In addition, advances in microelectronics, machine learning, material processing for new optical fibers and their relation with FSS are also discussed. These new developments on correlated areas can give rise for a new generation of sensors with advantageous features such as lower cost, easy connectivity, higher degree of customization and better performance.
关键词： Optical fiber sensors,Fiber specklegram sensors,Speckle metrology,Machine learning
更新于2025-09-11 14:15:04
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Scale Accuracy Evaluation of Image-Based 3D Reconstruction Strategies Using Laser Photogrammetry
摘要： Rapid developments in the field of underwater photogrammetry have given scientists the ability to produce accurate 3-dimensional (3D) models which are now increasingly used in the representation and study of local areas of interest. This paper addresses the lack of systematic analysis of 3D reconstruction and navigation fusion strategies, as well as associated error evaluation of models produced at larger scales in GPS-denied environments using a monocular camera (often in deep sea scenarios). Based on our prior work on automatic scale estimation of Structure from Motion (SfM)-based 3D models using laser scalers, an automatic scale accuracy framework is presented. The confidence level for each of the scale error estimates is independently assessed through the propagation of the uncertainties associated with image features and laser spot detections using a Monte Carlo simulation. The number of iterations used in the simulation was validated through the analysis of the final estimate behavior. To facilitate the detection and uncertainty estimation of even greatly attenuated laser beams, an automatic laser spot detection method was developed, with the main novelty of estimating the uncertainties based on the recovered characteristic shapes of laser spots with radially decreasing intensities. The effects of four different reconstruction strategies resulting from the combinations of Incremental/Global SfM, and the a priori and a posteriori use of navigation data were analyzed using two distinct survey scenarios captured during the SUBSAINTES 2017 cruise (doi: 10.17600/17001000). The study demonstrates that surveys with multiple overlaps of nonsequential images result in a nearly identical solution regardless of the strategy (SfM or navigation fusion), while surveys with weakly connected sequentially acquired images are prone to produce broad-scale deformation (doming effect) when navigation is not included in the optimization. Thus the scenarios with complex survey patterns substantially benefit from using multiobjective BA navigation fusion. The errors in models, produced by the most appropriate strategy, were estimated at around 1% in the central parts and always inferior to 5% on the extremities. The effects of combining data from multiple surveys were also evaluated. The introduction of additional vectors in the optimization of multisurvey problems successfully accounted for offset changes present in the underwater USBL-based navigation data, and thus minimize the effect of contradicting navigation priors. Our results also illustrate the importance of collecting a multitude of evaluation data at different locations and moments during the survey.
关键词： navigation fusion,laser scalers,uncertainty estimation,structure-from-motion,Monte Carlo simulation,laser spot detection,metrology,underwater 3D reconstruction,multiobjective BA,scale drift evaluation,photogrammetry
更新于2025-09-11 14:15:04
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Optimierter Laserspeckle-basierter Rauheitsmessprozess für bewegte, spiegelnde Oberfl?chen
摘要： This article describes the upcoming development of a parametric-optical laser measurement system for characterization of surfaces inline some production process. The measurement system is based on previously known approaches for characterization of specular surfaces using coherent light and auto-correlation on the resulting speckle intensity distribution. In order to apply these methods inline, a significantly increased measurement rate has to be reached, compared to existing solutions. This shall be achieved by modifications of the measurement process, use of hardware acceleration for image capturing and processing, and optimization of the processing algorithms.
关键词： speckle,Surface,hardware acceleration,FPGA,scattered light,roughness,laser,metrology
更新于2025-09-11 14:15:04
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[IEEE 2019 Joint Conference of the IEEE International Frequency Control Symposium anEuropean Frequency and Time Forum (EFTF/IFC) - Orlando, FL, USA (2019.4.14-2019.4.18)] 2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum (EFTF/IFC) - Earthquakes detection with optical fibers
摘要： The existing optical fiber network for telecommunication, together with coherent laser interferometry techniques such as narrow-linewidth lasers and heterodyne detection, is proposed as a tool for the detection of earthquakes. Using this infrastructure, we were able to detect several earthquakes, with moment magnitude as small as 3.4 and distances to the epicenter ranging between 25 and 18500 km. Such capability is extremely relevant for the detection of earthquakes in the seas and oceans, which are today poorly covered by bulk seismometers. We propose this technique as complementary to traditional detection and show how it can be established on the existing fiber network.
关键词： optical fiber link,frequency metrology,narrow-linewidth lasers,heterodyne detection,laser interferometry
更新于2025-09-11 14:15:04