High-speed reconfigurable spatiotemporal beam scanning enabled by a frequency-encoded optical phased array.

Two fast, CCD-based three-dimensional CT scanners for in vivo applications have been developed. One is designed for small laboratory animals and has a voxel size of 20 micrometer, while the other, having a voxel size of 80 micrometer, is used for human examinations. Both instruments make use of a novel multiple fan-beam technique: radiation from a line-focus X-ray tube is divided into a stack of fan-beams by a 28 micrometer pitch foil collimator. The resulting wedge-shaped X-ray field is the key to the instrument's high scanning speed and allows to position the sample close to the X-ray source, which makes it possible to build compact CT systems. In contrast to cone- beam scanners, the multiple fan-beam scanner relies on standard fan-beam algorithms, thereby eliminating inaccuracies in the reconstruction process. The projections from one single rotation are acquired within 2 min and are subsequently reconstructed into a 1024 X 1024 X 255 voxel array. Hence a single rotation about the sample delivers a 3D image containing a quarter of a billion voxels. Such volumetric images are 6.6 mm in height and can be stacked on top of each other. An area CCD sensor bonded to a fiber-optic light guide acts as a detector. Since no image intensifier, conventional optics or tapers are used throughout the system, the image is virtually distortion free. The scanner's high scanning speed and high resolution at moderately low radiation dose are the basis for reliable time serial measurements and analyses.

A 4kW Yb: YAG solid-state disc laser, with a four-way co-axial cladding head with powder feeding technique was employed to fabricate single-layer clads of Ni-based hardfacing alloy (Colmonoy-5) on medium carbon steel (ASME SA105) substrate by varying the laser processing parameters namely, beam power level (designated as low: 1200 W, medium: 1400 W, and high: 1600 W) and scanning speed (designated as low: 300 mm/min, medium: 400 mm/min, and high: 500mm/min). The laser clads were evaluated for their microstructural characteristics, microhardness, and slurry erosive wear performance with an aim to understand the effect of process parametric variations on their properties. Microstructural analyses of the clads were carried out using an optical microscope and a field-emission scanning electron microscope with attached energy-dispersive X-ray spectrometer supplemented by their Vickers microhardness testing and X-ray diffraction examination. The variation in laser processing parameters exerted a strong influence on the microstructural features of the clads in terms of γ-Ni dendrite size as well as morphology and distribution of various complex precipitates such as Cr-carbides and borides with relatively uniform distribution observed for the clads corresponding to low laser power and high scanning speed. The variation in laser power had relatively a greater influence on microhardness than the scanning speed variation. Micro-cutting, plastic deformation, crater formation besides ploughing away of the softer matrix were the typical fracture features associated with slurry eroded clads when examined under field-emission scanning electron microscope. Results of the slurry erosive wear tests showed that the clads pertaining to low laser power and high scanning speed exhibited superior wear resistance as compared to their counterparts.

Optical phased arrays (OPAs) are widely used in many applications to realize high-speed optical beam scanning. At present OPAs often suffer from limited scanning range. Here we propose a circular optical phased array (COPA) based on silicon photonics platform. According to our simulations, by positioning the OPA units in a circle and adopting a specific phase distribution, the COPA can realize 360° constant amplitude scanning. In addition, the design of the disk grating coupler, which is the key device of the COPA, is presented. The COPA is believed to have great potential for applications where a wide scanning range is mandatory.

The beam scanner is a predominant part in the light detection and ranging (LiDAR) system to achieve three-dimensional (3D) imaging. The solid-state beam-steering device has emerged as a promising candidate technology for a beam scanner with the advantages of robustness, stability, and high scanning speed. Here we propose a frequency modulated continuous wave (FMCW) LiDAR system with an in-fiber solid-state beam scanner. A 45° tilted fiber grating (TFG) is first employed to achieve in-fiber solid-state spectral scanning in the LiDAR system. A maximum output efficiency of 93.7% is achieved with proper polarization control. A single-mode fiber is then used to fabricate a 2-cm 45° TFG, which significantly reduces the size and the cost of the beam scanner in the LiDAR system. We experimentally realize 3D imaging of targets placed at a distance of 1.2 m based on our proposed LiDAR system. In addition, the system can achieve a detection distance of 6 m with a ranging precision of 24 mm.

A novel crack-free and refined 2195-Ti/CeB6 composites prepared by laser powder bed fusion

Frequently, at scientific meetings proteome researchers meet after the formal program has ended to discuss the state of the field and their own situation over some drinks. Typically these discussions center around instrumentation, primarily mass spectrometers, with a faster scan rate, higher mass accuracy or sensitivity, and the results generated by these powerful instruments. Statements like, “this is the future,” “this will revolutionize proteomics,” or “this has changed what we do in the lab” can be heard around the table. These sentiments are certainly justified. The progress in mass spectrometric instrumentation in the short history of proteomics has been nothing but astounding. Just a decade ago virtually all proteomic data were generated on ion trap instruments with low resolution, low mass accuracy, and limited scan speed and sensitivity, compared with the instruments presently in common use. Today, a significant fraction of the proteomic data is collected on high performance hybrid mass spectrometers with high scan speed, high mass accuracy and resolution, and high sensitivity of detection. The effects of these dramatic improvements are apparent in the manuscripts being published. However, its importance notwithstanding, data collection is only half of the whole proteomic story. The capacity to annotate, analyze, store, manage, and distribute the many gigabytes of data collected is the other half of the proteomic technology tandem. Long gone are the days when the expert analyst pretended to have manually verified all the data supporting the conclusions in a proteomic paper. Therefore, proteomics today, particularly mass spectrometry-based proteomics, depends as much on computers and the software tools they use as it does on high tech instruments to generate the data. Surprisingly, at the sessions in the bar, no one ever seems to boast about the data analysis part of the proteomic enterprise. Statements such as “ this program just recovered 20% more true positive peptide identification from my data set,” “ this allowed me to analyze my data ten times faster and at a credible FDR,” or “this statistical model allowed me to identify statistically significant quantitative changes in my dataset” are seldom if ever uttered. It is unlikely that things in the realm of electronics and software are inherently less appealing or attractive than high performance devices because the same individuals boasting about their mass spectrometers are likely to also share interesting new iPhone apps. It is certainly also not the case that advances on the software side of proteomics have had a lower impact than publications describing new hardware. In fact some of the most highly cited proteomics papers are about software. I therefore propose the likely controversial thesis that the software world of proteomics is less generally discussed because few can keep up and know about the field in some depth. This view is supported by several observations. First, in a recent study (1), in which a standardized protein sample was analyzed by a number of laboratories, it was clearly apparent that the analysis of the collected data was a major weakness. Second, the adoption of new software tools for proteomic data analysis takes much longer than the adoption of new instruments or wet-lab protocols. To raise the level of awareness in the crucial area of proteomic software tools, Molecular and Cellular Proteomics will publish a series of mini reviews that summarize the current state of specific aspects of this often bewildering field. These are not tutorials, i.e. the reader still will have to figure out how to use the tools and which tools to use. The intent of this series is to discuss the significance of a particular type of analysis, the question(s) addressed, the currently available solutions and their strengths and weaknesses, and the availability and utility of germane software tools or computational resources. We expect that these mini reviews will help proteome researchers to extract more and better information from the data generated by the wonderful instruments available today and to increase the excitement about the topic so that statistical models, search engines, and XML schema can also claim the stature in bar discussions that they deserve.

Fabrication of orientated micro porous metals: Control the melting process of powders by high scanning speed - ultra short hatch spacing scanning strategy

The synthesis of catalysis-relevant nanoparticles such as platinum and gold is demonstrated with productivities of 4 g h−1 for pulsed laser ablation in liquids (PLAL). The major drawback of low productivity of PLAL is overcome by utilizing a novel ultrafast high-repetition rate laser system combined with a polygon scanner that reaches scanning speeds up to 500 m s−1. This high scanning speed is exploited to spatially bypass the laser-induced cavitation bubbles at MHz-repetition rates resulting in an increase of the applicable, ablation-effective, repetition rate for PLAL by two orders of magnitude. The particle size, morphology and oxidation state of fully automated synthesized colloids are analyzed while the ablation mechanisms are studied for different laser fluences, repetition rates, interpulse distances, ablation times, volumetric flow rates and focus positions. It is found that at high scanning speeds and high repetition rate PLAL the ablation process is stable in crystallite size and decoupled from shielding and liquid effects that conventionally occur during low-speed PLAL.

Microstructure and mechanical properties of WC-12Co cemented carbide fabricated by laser powder bed fusion on a WC-20Co cemented carbide substrate

In this study, the relationship between solidification cracking and epitaxial growth behavior with the high-speed laser surface melting of a directionally solidified 247LC superalloys was fundamentally and metallurgically investigated, to develop a successful welding procedure for the next generation of gas turbine blades. Under typical laser surface melting conditions (scan speed: 50 mm/s, heat input: 40 J/mm), severe solidification cracking phenomena occurs. The key metallurgical factors of solidification cracking have been identified as solidification segregation-assisted pipeline diffusion behavior at the solidification grain boundary, and in the randomly formed polycrystalline melting zone microstructure. In addition, under extremely low heat input and high-speed laser beam scan conditions (scan speed: 1000 mm/s, heat input: 2 J/mm), an effective surface melting zone can be obtained within a single directionally solidified grain under a relatively high-energy beam density (65 J/mm2) using the characteristics of single-mode fiber lasers. Results reveal that the laser melting zone successfully shows a 99.9% epitaxial growth achievement ratio. Because of the superior epitaxial growth ratio within the laser surface melting zone, and the rapid solidification phenomena, formation of a solidification grain boundary and solidification segregation-assisted pipeline diffusion behavior can be suppressed. Finally, a solidification crack-free laser melting zone can thus be achieved.

In this study, Ti-22Al-25Nb intermetallic compound alloys are fabricated through selective laser melting (SLM) at four scanning speeds (600, 700, 800, and 900 mm/s). The microstructure and mechanical properties of the selective laser melting fabricated alloys are systematically evaluated. The results indicate that scanning speed significantly affects microstructure characteristics (e.g., relative density, grain size, texture density, and the precipitation of secondary phases). The variation laws of the relative density, grain size, and texture density are likewise affected by scanning speed. The relative density, grain size, and texture density increase and then decrease with the increase in scanning speed. The alloy fabricated with the lowest scanning speed (600 mm/s) exhibits the maximum relative density, grain size, and texture density. By contrast, the alloy with the highest scanning speed (900 mm/s) exhibits the minimum relative density, grain size, and texture density. Furthermore, the precipitations of the O phase and Ti3Al phase are primarily distributed in regions with a high strain concentration near the pool boundary. The alloy fabricated with a 600 mm/s scanning speed simultaneously achieves the highest strength and elongation, which is closely correlated with the uniform distribution of secondary phases.

PurposeThis study aims to investigate the relationship between melt pool dimensions and acoustic emission (AE) signal magnitudes obtained during laser powder bed fusion (L-PBF) process of austenitic stainless steel. Specifically, by varying laser power and scan speed, the widths, depths and aspect ratios of melt pools were compared with AE signal magnitudes across a frequency range of 100–200 kHz.Design/methodology/approachExperiments were conducted under different laser powers at a fixed scan speed and scan speeds at a fixed laser power. Melt pool dimensions were measured from cross-sectional optical images, and AE signals were obtained using a piezoelectric AE sensor installed beneath the build plate. Short-Time Fourier Transform (STFT) was applied to AE signals, and the magnitudes of frequency components were obtained.FindingsA strong correlation between melt pool dimensions and STFT magnitude was obtained. Pearson correlation coefficients between melt pool dimensions and STFT magnitudes were above 0.9 and the p-values were below 0.05. Increasing the laser energy enlarged the volume of melt pool and intensified the oscillation of melt pool. When scan speed exceeded 1,100 mm/s, STFT magnitude showed a slight increase owing to the increase in the vapor pressure.Originality/valuePrevious studies used AE signals to detect defects, but this study found a correlation between STFT magnitude and melt pool dimensions in L-PBF process. It was also found that STFT magnitude was more affected by vapor pressure at higher scan speeds. Monitoring STFT magnitude can help to understand melt pool dynamics, maintain process consistency and identify irregularities in real time.

Improvement of densification and microstructure of ASTM A131 EH36 steel samples additively manufactured via selective laser melting with varying laser scanning speed and hatch spacing

In the presented study, the laser transformation hardening of commercially pure titanium sheet material of thickness being 1.6mm is investigated using CW, 1.6 kW solid State Nd: YAG laser. A Full Factorial Design (FFD) with Response Surface Methodology (RSM) is employed to establish, optimize and to investigate the relationships of three laser transformation hardening process parameters such as laser power, scanning speed, and focused position on laser hardened bead profile parameters such as hardened bead width, hardened depth, heat input and power density. In this work, Laser Transformation Hardening (LTH) with high precision and an optimum desired minimum value of hardened depth of 241 microns has been accomplished with heat input = 150 J/cm and power density = 294.08 W/mm2 for the laser process parameters of lower beam power: 750 Watts, high scanning speed: 3000 mm/min and a defocused beam of –30 mm. Effects of laser process parameters on laser hardened bead geometries were carried out using RSM. Results indicate that the scanning speed has a positive effect on all hardened bead dimensions while the laser power has a positive effect particularly on hardened bead width as compared to hardened depth and heat input. The optimum laser hardening conditions are identified sequentially to minimise hardened depth, heat input, power density and maximum hardened bead width. The validation results demonstrate that the developed models are accurate with low percentages of error.

The time evolution of the temperature profile during cw laser processing is calculated including the effects of melting using computer simulation. Results, presented for single-crystal silicon irradiated by an argon ion cw laser, show that high scanning speed can result in a non-steady-state situation for the temperature rise. In this case the maximum temperature and melt depth become functions of the dwell time and also less sensitive to the incident laser power, as a result of which scanning speed can be effectively used to control melting process induced by cw laser. Experimental results presented support the calculated dependence of the maximum melt depth on the laser power and scanning speed.