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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) - Sign-Alternating Dispersion Patterning for Supercontinuum Generation
摘要： Supercontinuum generation (SCG), a process that generates a wide and coherent bandwidth of light, has become foundational in emergent optical technologies in a plethora of fields, such as optical coherence tomography (OCT), metrology (e.g., integrated photonic Kerr combs) and precision sensing. As advanced applications of SCG emerge, the requirements on the spectral bandwidth, the coherence, its temporal compressibility, and the quality of the optical spectral content (e.g., a uniformly flat spectral profile) are increasing. Moreover, as these technologies need not be restricted to the lab, the spectral conversion efficiency of SCG must increase from current technology that functions, e.g., in the tens of nJ pulse energy, to sub nJ levels.
关键词： precision sensing,optical coherence tomography,spectral bandwidth,coherence,metrology,Supercontinuum generation,spectral conversion efficiency,temporal compressibility
更新于2025-09-16 10:30:52
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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) - Scrutinizing the Equidistance of Frequency Comb Sources
摘要： Frequency combs have revolutionized frequency metrology, enabling optical clockworks with unprecedended precisions approaching the 10-18 range. Early frequency comb measurements exclusively relied on mode-locked lasers, which provide a periodic waveform as a matter of working principle. In turn, the resulting frequency comb is guaranteed to be absolutely equidistant. While this expectation is ultimately based on theoretical mode-locking models, experimental tests have scrutinized deviations from equidistance of mode-locked laser combs down to the 10-15 level. Experimental tests of equidistance are rather elaborate and typically require beating of different spectral parts of the comb with a reference comb. Such tests have also been performed with microresonator combs, which are not a priori guaranteed to be equidistant from theoretical considerations. Finally, there are rather recent reports of quantum cascade laser combs; yet careful investigations of the equidistance of such sources still appear to be outstanding. Here we propose and demonstrate a novel experimental test for the equidistance of frequency combs.
关键词： metrology,frequency combs,mode-locked lasers,equidistance
更新于2025-09-16 10:30:52
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Versitile X-ray diagnostics of laser-produced high-temperature plasmas using an ultra-high luminosity spectrometer
摘要： Versitile diagnostics of high-temperature magnesium laser-produced plasmas is performed using an ultra-high luminosity X-ray focusing crystal spectrometer. The plasmas are produced by focusing nanosecond laser pulses (0.53 mm, 1 J, 2 ns) on a massive magnesium target. The absolute intensities and X-ray yields are measured for the resonance lines of H- and He-like ions (spectral range: D?l = 8 –10 ?), the electron temperature of plasmas is determined (range: Te = 200 – 550 eV), and the behaviour of these parameters is established in a broad range of laser pulse energy EL (10 mJ – 1 J). This approach permits the parameters of laser-plasma radiation sources to be monitored in real time in a wide intensity range (difference in intensity: over 104) and in a broad range of plasma parameters.
关键词： laser-produced plasmas,X-ray spectrometers,high-temperature plasma diagnostics,X-ray spectroscopy and metrology,multiply charged ions
更新于2025-09-16 10:30:52
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[IEEE 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Guangzhou, China (2019.5.19-2019.5.22)] 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Dual-band tunable mid-infrared polarization converter based on U-shaped graphene metamaterial
摘要： 3-D coordinate transformation, which is based on aligning two sets of common reference points, is frequently applied in large-scale combined measurement to unify coordinate frames and tie individual measurement systems together. However, it introduces uncertainty into the ?nal measurement results. This uncertainty must be quanti?ed to make the results complete. This paper presents a novel approach to the uncertainty analysis of 3-D coordinate transformation based on the weighted total least squares adjustment. This approach takes full account of the uncertainty characteristics of measuring instruments and is simple in calculation. In this approach, the transformation uncertainty of a point in a world frame is analyzed carefully. The simulations show that the transformation uncertainty has a distribution of concentric ellipsoids and is affected by the measurement uncertainties and layout of common points. Besides, strategies for minimizing transformation uncertainty are recommended. The experimental results from a laser tracker prove that this proposed approach is valid under normal instrument operating conditions and that these strategies are feasible and ef?cient.
关键词： Coordinate transformation,error analysis,uncertainty,large-scale metrology,position measurement,sensor fusion
更新于2025-09-16 10:30:52
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Hydrodynamic modeling and time-resolved imaging reflectometry of the ultrafast laser-induced ablation of a thin gold film
摘要： The ablation of thin metal films using ultrafast laser radiation represents a standard processing procedure in laser technology. However, looking closer to the resulting structures, the arising topology deviates strongly from the expected one. Ablation of thin gold films using ultrafast laser radiation with a Gaussian-shaped spatial intensity distribution results in flat topologies. By synergistically combining space and time-resolved reflectometry with expanded two-temperature hydrodynamic modeling, we explain the formation of bulging and rupture of the thin film-surface by the expansion of strongly stretched liquid material due to the induced rarefaction wave propagating towards the substrate. Also, the formation of a flat ablation structure is described by the interplay of two rarefaction waves, one propagating towards the substrate and the other one propagating towards the vacuum boundary, within the completely molten film. The simulated topology agrees excellent with the experimentally observed ablation structure. Besides, all simulated stages of excitation of the gold film, namely electron-phonon non-equilibrium, hydrodynamic expansion, and rupture, are confirmed by space and time-resolved pump-probe reflectometry.
关键词： Imaging reflectometry,Thin film ablation,Femtosecond laser radiation,Two temperature model hydrodynamics (TTMHD),Gold thin film,Ultrafast metrology
更新于2025-09-16 10:30:52
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Thermal Deformation Compensation of Laser Tracker Relocating in Aircraft Assembly
摘要： During aircraft assembly, measurements from either a single or multiple laser tracker with different positions are transformed to an assembly coordinate system by measuring the enhanced reference system (ERS) points via a rigid-body registration method. The location deviations of the ERS points resulting from thermal deformations have become the major error source in registration. To improve the accuracy of measurement, a thermal deformation compensation method, based on precise thermal deformation theory, is proposed in this study. Thermal deformation coefficients of ERS points in X-, Y-, and Z-axes are calculated separately, and an iterative algorithm is developed to correct the actual locations of the ERS points and estimate the optimal coordinate transformation parameters. A case study indicated that, with our proposed novel thermal deformation compensation method, the average registration error is decreased by 9.2–38.7%, and the maximum registration error is deceased by 12.3–38.6%.
关键词： Laser tracker relocating,Thermal deformation coefficient,Enhanced reference system point,Location deviation,Large-volume metrology
更新于2025-09-16 10:30:52
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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) - Accurate and Traceable Determination of Raman Shifts in Reference Material by Continuous-Wave Stimulated Raman Spectroscopy
摘要： Most Raman spectrometers require frequent calibration in order to provide accurate and repeatable results, and the calibration interval decreases for operation at high resolution. Wavenumber calibration commonly uses emission lines from gas-discharge lamps (e.g. mercury, neon, argon) that provide well-defined frequencies with very low uncertainties. However, it is often impractical to align lamps properly at the sample position, and the lamp emission lines provide absolute frequencies rather than Raman shifts. A more practical alternative is the use of a reference sample with a known Raman spectrum, which allows for the calibration of Raman spectrometer regardless of the excitation wavelength. Polystyrene is commonly used as a reference as it is easily available and practical to handle. We report on the application of continuous-wave stimulated Raman spectroscopy (CW-SRS) for accurate measurement of Raman shifts in polystyrene samples. Due to the narrow linewidth of CW radiation, CW-SRS achieves spectral resolution that is several orders of magnitude below those obtained with common Raman spectrometer or pulsed-based SRS. Furthermore, CW-SRS enables direct determination of the Raman shift by measuring the difference of pump and probe frequencies. For our application, we used an 852 nm diode laser as probe and a widely tunable external cavity diode laser as pump covering the wavelength range from 781 nm to 787 nm. Stimulated Raman gain was measured by modulating the pump amplitude at 10.4 MHz and detecting scattered light on the probe with a balanced photodetector and spectrum analyser. High frequency modulation and balanced detection ensured shot noise limited operation, which was confirmed by the scaling of the noise level and signal with probe power up to 4.5 mW (Fig. 1 (b)). Polystyrene spectra in the range 968 cm-1 to 1059 cm-1 were recorded by scanning the pump wavelength. Both pump and probe wavelengths were measured accurately by a wavelength meter traceable to a frequency standard. Values and uncertainties of the Raman shift of two Raman transitions in polystyrene were calculated according to the Guide to the Expression of Uncertainty in Measurement (GUM) [1]. The method was applied to two different polystyrene samples: a thin plate taken from a tool cabinet and a NIST traceable reference sample for FTIR. For the later, Raman shifts of 1001.15 ± 0.04 cm-1 and 1031.33 ± 0.21 cm-1 were measured. Compared with existing standards [2], we achieve up to one order of magnitude improvement on the uncertainty of the measured Raman shifts, thereby improving the metrology capability for characterization of reference material for Raman spectroscopy. Furthermore, shot noise operation paves the way towards the development of quantum-enhanced SRS with potential application in biological imaging.
关键词： Raman spectroscopy,continuous-wave stimulated Raman spectroscopy,metrology,polystyrene,calibration
更新于2025-09-12 10:27:22
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In-process height control during laser metal deposition based on structured light 3D scanning
摘要： Laser metal deposition is an additive manufacturing process capable of layer by layer construction of solid parts. An incorrect deposition distance between nozzle and substrate can result in height deviations from the ideal building path. The error can be propagated along layers, leading to an irreversible defect. Maintaining an optimal distance between the nozzle and the substrate is therefore a critical aspect. This paper introduces an off-line geometric control system for in-process measurement and build path correction. A structured light based 3D scanner measures the build height from an external, fixed position, providing more precise results than moving measuring systems. The deposition is stopped in certain stages of the process and the piece is scanned generating a three-dimensional point cloud. Processing of the collected data allows the build height determination. A control algorithm was developed to take corrective actions in accordance with the measured error. The system enables an accurate control of the generated geometry and permits the comparison with the original computer design. This approach reduces the required human supervision during the process and the occurrence of non-valid parts. The effectiveness of the method was proved through the contrast of parts built with and without control, showing a more accurate reproduction of the generated solid parts when corrections are applied.
关键词： monitoring,Laser Metal Deposition (LMD),additive manufacturing,control,metrology,structured light,3D scanning
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) - Planar Optical Antennas as Efficient Single-Photon Sources for Free-Space and Fiber-Based Operation in Quantum Optics and Metrology
摘要： Practical implementations of quantum technologies, ranging from optical quantum computing to metrological measurements, suffer from the lack of high-rate, on-demand sources of indistinguishable single photons. We will discuss a simple and versatile planar optical antenna, showing both theoretical and experimental evidence of low-loss (< 20%) beaming of the radiation from a single quantum emitter into a narrow cone of solid angles in free space, which allows in principle up to 50% coupling into a single-mode fiber. In particular, we will first present an experimental implementation of the design operated at room temperature, exploiting Dibenzoterrylene molecules (DBT) hosted in a crystalline anthracene matrix (Ac) [1]. The DBT:Ac system is particularly suitable for this task, due to its outstanding photo-physical properties (i.e. long-term photostability both at room and cryogenic temperature, lifetime-limited emission at cryogenic temperatures, 780 nm operating wavelength) demonstrated in 50 nm-thick crystals [2] and recently also in nanocrystals [3]. Moreover, single photons from DBT molecules and similar [4] result very appealing concerning quantum communication and computation protocols which involve quantum memories, due to the unmatched stability and narrowness of their spectrum (below 100 MHz). Then we will report on our theoretical study to determine the ultimate performances attainable with such design in case of operation in cryogenic environment, exploring materials and fine tuning of geometrical parameters. We will finally discuss our recent results about a single-mirror antenna operating at cryogenic temperature. We demonstrate a photon flux in the Fourier-limited line higher than 1MHz at detectors, and coupling of fluorescence into single-mode fibers up to 46%. These results open to the deploiment of our system both in quantum optics experiments requiring deterministic single-photon sources and in metrology, in particular for a new operative definition of the candela, as recently proposed in the EMPIR project 'SIQUST' [5].
关键词： Quantum Optics,Single-Photon Sources,Dibenzoterrylene molecules,Metrology,Planar Optical Antennas,Crystalline anthracene matrix
更新于2025-09-12 10:27:22
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On Optimising Spatial Sampling Plans for Wafer Profile Reconstruction ? ?The second author gratefully acknowledges the financial support provided by Irish Manufacturing Research (IMR) for this research.
摘要： Wafer metrology is an expensive and time consuming activity in semiconductor manufacturing, but is essential to support advanced process control, predictive maintenance and other quality assurance functions. Keeping metrology to a minimum is therefore desirable. In the context of spatial sampling of wafers this has motivated the development of a number of data driven methodologies for optimizing wafer sampling plans. Two such methodologies are considered in this paper. The first combines Principal Component Analysis and Minimum Variance Estimation (PCA-MVE) to determine an optimum subset of sites from historical metrology data from a larger candidate set, while the second employs Forward Selection Component Analysis (FSCA), an unsupervised variable selection technique, to achieve the same result. We investigate the relationship between these two approaches and show that under specific conditions a regularized extension of FSCA, denoted FSCA-R, and PCA-MVE are equivalent. Numerical studies using simulated data verify the equivalence conditions. Results for simulated and industrial case studies show that the improvement in wafer profile reconstruction accuracy with regularization is not statistically significant for the case studies considered, and that when PCA-MVE is implemented with a denoising step as originally proposed, it is outperformed by FSCA. Therefore, FSCA is the preferred methodology.
关键词： spatial sampling,Principal Component Analysis,Forward Selection Component Analysis,semiconductor manufacturing,wafer site selection,metrology
更新于2025-09-12 10:27:22