- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Analysis and Design of a CMOS Ultra-High-Speed Burst Mode Imager with In-Situ Storage Topology Featuring In-Pixel CDS Amplification
摘要： This paper presents an in-situ storage topology for ultra-high-speed burst mode imagers, enabling low noise operation while keeping a high frame depth. The proposed pixel architecture contains a 4T pinned photodiode, a correlated double sampling (CDS) amplification stage, and an in-situ memory bank. Focusing on the sampling noise, the system level trade-off of the proposed pixel architecture is discussed, showing its advantages on the noise, power, and scaling capability. Integrated with an AC coupling CDS stage, the amplification is obtained by exploiting the strong capacitance to the voltage relation of a single NMOS transistor. A comprehensive noise model is developed for optimizing the trade-off between the area and noise. As a proof-of-concept, a prototype imager with a 30 μm pixel pitch was fabricated in a CMOS 130 nm technology. A 108-cell memory bank is implemented allowing dense layout and parallel readout. Two types of CDS amplification stages were investigated. Despite the limited memory capacitance of 10 fF/cell, the photon transfer curves of both pixel types were measured over different operation speeds up to 20 Mfps showing a noise performance of 8.4 e?.
关键词： burst mode,million frames per second,ultra-high-speed imaging,in-pixel amplification,in-situ storage,image sensors
更新于2025-09-23 15:21:01
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3D particle tracking velocimetry for the determination of temporally resolved particle trajectories within laser powder bed fusion of metals
摘要： Within this work, we present a system for the measurement of the three-dimensional (3D) trajectories of spatters and entrained particles during laser powder bed fusion (L-PBF) of metals. It is comprised of two ultrahigh-speed cameras and a reconstruction task specific processing reconstruction algorithm. The system enables an automated determination of 3D measures from the trajectories of a large number of tracked particles. Ambiguity evolving from an underdetermined geometrical situation induced by a two-camera setup is resolved within the tracking using a priori knowledge of L-PBF of metals. All processing steps were optimized to run on a graphics processing unit to allow the processing of large amounts of data within an appropriate time frame. The overall approach was validated by a comparison of the measurement results to synthetic images with a known 3D ground truth.
关键词： laser,high-speed imaging,3D particle velocimetry,image processing,additive manufacturing,powder bed fusion
更新于2025-09-23 15:19:57
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Versatile high-speed confocal microscopy using a single laser beam
摘要： We present a new flexible high speed laser scanning confocal microscope and its extension by an astigmatism particle tracking velocimetry (APTV) device. Many standard confocal microscopes use either a single laser beam to scan the sample at a relatively low overall frame rate or many laser beams to simultaneously scan the sample and achieve a high overall frame rate. The single-laser-beam confocal microscope often uses a point detector to acquire the image. To achieve high overall frame rates, we use, next to the standard 2D probe scanning unit, a second 2D scan unit projecting the image directly onto a 2D CCD-sensor (re-scan configuration). Using only a single laser beam eliminates crosstalk and leads to an imaging quality that is independent of the frame rate with a lateral resolution of 0.235 μm. The design described here is suitable for a high frame rate, i.e., for frame rates well above the video rate (full frame) up to a line rate of 32 kHz. The dwell time of the laser focus on any spot in the sample (122 ns) is significantly shorter than those in standard confocal microscopes (in the order of milli- or microseconds). This short dwell time reduces phototoxicity and bleaching of fluorescent molecules. The new design opens up further flexibility and facilitates coupling to other optical methods. The setup can easily be extended by an APTV device to measure three dimensional dynamics while being able to show high resolution confocal structures. Thus, one can use the high resolution confocal information synchronized with an APTV dataset.
关键词： APTV,high-speed imaging,astigmatism particle tracking velocimetry,confocal microscopy,single laser beam
更新于2025-09-23 15:19:57
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Microscopy of the Heart || Optical Sectioning Microscopy at ‘Temporal Super-Resolution’
摘要： Within the recent years several super-resolution microscopic methods were developed, where the super-resolution refers to bringing the optical resolution beyond the diffraction limit introduced by Ernst Abbe, which was believed to be a real limit for quite some time. The popularity of the method also in cardiac related research can be followed in the chapter ‘Quantitative super-resolution microscopy of cardiac myocytes’ in this book. In parallel to this spatial super-resolution progress, within the past two decades there was a dynamic development of high speed–high resolution imaging initially towards video-rate (30 frames per second, also referred to as ‘real time’-imaging) but soon to ever increasing frame rates reaching the kHz order of magnitude these days. Many processes, especially those in excitable cells such as neurons and cardiomyocytes [1] or cells in ?ow like erythrocytes or leukocytes [2], require even higher temporal resolution to elucidate the kinetics of processes like the Excitation-Contraction Coupling (ECC). Such ultra high speed recordings still require a diffraction limited spatial resolution to correlate function and subcellular structures [3]. Within this chapter we review optical sectioning microscopy and their application in cellular cardiology. In this approach we focus on methods that allow to access any part of the cell, i.e. we exclude methods that are intrinsically limited to surface investigations like total internal re?ection ?uorescence (TIRF) microscopy [4] or scanning near ?eld optical microscopy (SNOM) [5]. In similarity we exclude techniques that require several images to calculate an image section such as deconvolution microscopy [6] or structured illumination microscopy [7] (e.g., Apotome.2, Zeiss, Jena, Germany).
关键词： super-resolution microscopy,Excitation-Contraction Coupling,high-speed imaging,cardiomyocytes,optical sectioning
更新于2025-09-23 15:19:57
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Influence of Magnesium on Spatter Behavior in Laser Deep Penetration Welding of Aluminum Alloys
摘要： The quality of welds, as well as the necessity of post-processing, is challenged by spatter generation during the laser keyhole welding process. In this study, the influence of the magnesium content on spatter behavior is studied for three aluminum alloys (Al99.5, AlMg3, and AlMg5). A synchronized dual high-speed camera system is used to observe the spatter behavior and to reconstruct 3D spatter trajectories as well as determine the characteristics of spatter velocity, flight path angle, and approximate spatter size. The mean spatter velocities and flight path angles of the welding experiments with the three alloys were in welding direction between 4.1 m/s and 4.6 m/s and 44.8°, respectively. Furthermore, the AlMg alloys show excessive spatter behavior with spray events of more than 50 spatters at a time, and less frequently spatter explosions. Spatter spray events show a character similar to spatter explosions. Volumetric evaporation is proposed as effecting these events. In contrast, and resulting from a different mechanism, pure aluminum (Al99.5) shows group ejection events with at least 10 spatters at a time. In this study, there are no correlations between spatter velocities and flight path angles, nor between velocities and approximate spatter sizes.
关键词： high-speed imaging,keyhole welding,aluminum alloy,welding,laser welding,spatter
更新于2025-09-19 17:13:59
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Laser metal deposition of copper on diverse metals using green laser sources
摘要： Green laser sources are advantageous in the processing of copper due to the increase of absorptivity compared with more commonly available infrared lasers. Laser metal deposition of copper with a green laser onto various substrate metals namely copper, aluminium, steel and titanium alloy was carried out and observed through high-speed imaging. The effects of process parameters such as laser power, cladding speed and powder feed rate, and material attributes such as absorptivity, surface conditions and thermal conductivity are tied together to explain the size and geometry of the melt pool as well as the fraction of the power used for melting material. The copper substrate has the smallest melt pool with a high angle, followed by aluminium, steel and titanium alloy. The incorporation times for powder grains in the melt pools vary based on the substrate materials. Its dependency on material properties, including surface tension forces, melting temperatures and material density, is discussed. Oxide skins present on melt pools can affect powder incorporation, most significantly on the aluminium substrate. The lower limits of the fraction of power irradiated on the surface used purely for melting were calculated to be 0.73%, 2.94%, 5.95% and 9.78% for the copper, aluminium, steel and titanium alloy substrates, respectively, showing a strong dependence on thermal conductivity of the substrate material. For a copper wall built, the fraction was 2.66%, much higher than a single clad on a copper substrate, due to reduced workpiece heating. The results of this paper can be transferred to other metals with low absorptivity such as gold.
关键词： Multi-material,DED,High-speed imaging,LMD,Copper,Green 515-nm laser,Laser metal deposition,Powder grain incorporation,Additive manufacturing,Directed energy deposition,Absorptivity
更新于2025-09-19 17:13:59
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Laser-induced forward transfer of soft material nanolayers with millisecond pulses shows contact-based material deposition
摘要： In this work, we present a qualitative and quantitative experimental analysis, as well as a numerical model, of a novel variant of the laser-induced forward transfer, which uses millisecond laser pulses. In this process, soft material nanolayer spots are transferred from a donor slide, which is coated with the soft material layer, to an acceptor slide via laser irradiation. This method offers a highly flexible material transfer to perform high-throughput combinatorial chemistry for the generation of biomolecule arrays. For the first time, we show visual evidence that the main transfer mechanism is contact-based, due to thermal surface expansion of the donor layer. Thus, the process is different from the many known variants of laser-induced forward transfer. We will characterize the maximum axial surface expansion in relation to laser power and pulse duration. On this basis, we derive a numerical model that approximates the axial surface expansion within measurement tolerances. Finally, we analyze the topology of the transferred soft material nanolayer spots by fluorescence imaging and vertical scanning interferometry to determine width, height, and shape of the transferred material. Concluding from this experimental and numerical data, we can now predict the amount of transferred material in this process.
关键词： high-speed imaging,fluorescence imaging,experimental and numerical prediction,vertical scanning interferometry,OpenFOAM
更新于2025-09-12 10:27:22
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Laser induced cavitation: Plasma generation and breakdown shockwave
摘要： Laser induced cavitation is one of the effective techniques to generate controlled cavitation bubbles, both for basic study and for applications in different fields of engineering and medicine. Unfortunately, control of bubble formation and symmetry is hardly achieved due to a series of concurrent causes. In particular, the need to focus the laser beam at the bubble formation spot leads, in general, to a conical region proximal to the light source where conditions are met for plasma breakdown. A finite sized region then exists where the electric field may fluctuate depending on several disturbing agents, leading to possible plasma fragmentation and plasma intensity variation. Such irregularities may induce asymmetry in the successive bubble dynamics, a mostly undesired effect if reproducible conditions are sought for. In the present paper, the structure of the breakdown plasma and the ensuing bubble dynamics are analyzed by means of high speed imaging and intensity measurements of the shockwave system launched at breakdown. It is found that the parameters of the system can be tuned to optimize repeatability and sphericity. In particular, symmetric rebound dynamics is achieved almost deterministically when a pointlike plasma is generated at the breakdown threshold energy. Spherical symmetry is also favored by a large focusing angle combined with a relatively large pulse energy, a process which, however, retains a significant level of stochasticity. Outside these special conditions, the elongated and often fragmented conical plasma shape is found to be correlated with anisotropic and multiple breakdown shockwave emission.
关键词： high speed imaging,Laser induced cavitation,bubble dynamics,breakdown shockwave,plasma generation
更新于2025-09-12 10:27:22
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Quantitative study of melt flow dynamics inside laser cutting kerfs by in-situ high-speed video-diagnostics
摘要： Within this paper the melt flow dynamics of the laser cutting process during laser cutting of 6 mm thick stainless-steel using a disk laser with a laser power of 5 kW and nitrogen assist gas with a pressure up to 20 bar, is analyzed by in-situ high-speed video-diagnostics (>100,000 fps). An advanced algorithm is used to determine spatially resolved the melt flow dynamics on the laser cutting front. The results reveal a link between the fluid dynamics, the cutting velocity, the assist gas pressure and the average roughness of the cut flank.
关键词： melt flow,process diagnostics,high-speed imaging,1 micron laser,Laser cutting
更新于2025-09-12 10:27:22
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Influence of the vapour channel on processing in laser powder bed fusion
摘要： Additive Manufacturing provides many opportunities to design and manufacture parts that are difficult or not possible to produce with conventional methods. In Selective Laser Melting (SLM) in powder bed fusion (PBF), melt pool dynamics and stability is dependent on a large number of factors, e.g. laser power output, power density, travel speed, reflectivity of powder bed, rapid heating and vaporization. Since travel speeds are often very fast and the laser interaction zone is small, the physical events become difficult to predict but also to observe. This work aims to describe the formation and geometrical characteristics of the vaporization zone during processing. Using a combination of theoretical descriptions, resulting material structures and a comprehensive analysis of high-speed images of the processing zone for different heat inputs and travel speeds, explanations for the dynamic melt pool behaviour are derived. The melting and pressures from processing involved moves powder particles next to it, changing the conditions for neighbouring tracks due to lack of material. These findings can provide a basis for creating more efficient and stable SLM processing, with fewer imperfections.
关键词： High speed imaging,Pressure,Powder movement,SLM
更新于2025-09-12 10:27:22