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[IEEE 2019 IEEE High Power Diode Lasers and Systems Conference (HPD) - Coventry, United Kingdom (2019.10.9-2019.10.10)] 2019 IEEE High Power Diode Lasers and Systems Conference (HPD) - The requirements on pulsed laser diodes for use in atmospheric LiDAR
摘要： A novel technique for parameterizing surface roughness in coastal inundation models using airborne laser scanning (lidar) data is presented. Two important parameters to coastal overland flow dynamics, Manning’s n (bottom friction) and effective aerodynamic roughness length (wind speed reduction), are computed based on a random forest (RM) regression model trained using field measurements from 24 sites in Florida fused with georegistered lidar point cloud data. The lidar point cloud for each test site is separated into ground and nonground classes and the z-dimensional (height or elevation) variance from the least squares regression plane is computed, along with the height of the nonground regression plane. These statistics serve as the predictor variables in the parameterization model. The model is then tested using a bootstrap subsampling procedure consisting of removal without replacement of one record and using the surviving records to train the model and predict the surface roughness parameter of the removed record. When compared with the industry standard technique of assigning surface roughness parameters based on published land use/land cover type, the RM regression models reduce the parameterization error by 93% (0.086–0.006) and 53% (1.299–0.610 m) for Manning’s n and effective aerodynamic roughness length, respectively. These improvements will improve water level and velocity predictions in coastal models.
关键词： lidar,Manning’s n,random forest (RM),land cover,Aerodynamic roughness
更新于2025-09-23 15:19:57
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Laser Cutting Parameters Effect on 316L Stainless Steel Surface
摘要： Laser cutting is a cutting technology that enables fast processing in high precision. This technology utilizes high temperatures generated by engine to perform the cutting process. Selection of cutting parameters becomes the main factor to determine the cutting surface quality. Cutting parameters in the form of cutting speed and gas pressure are varied between 60 mm/minute - 100 mm/minute and 17 bar - 21 bar to examine the effect on surface character. The character of the laser-cutting surface on 316L series stainless steel material was observed related to the roughness, hardness and microstructure. The results showed that the parameters of cutting speed and gas pressure had an effect on the cutting surface. Changes in cutting speed has more effect on surface roughness while gas pressure has more effect on cutting surface hardness. Observations on the surface also illustrated that there were differences in cutting quality along with the deeper penetration performed by the laser.
关键词： gas pressure,hardness,cutting speed,surface roughness
更新于2025-09-23 15:19:57
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Experimental investigation on the machining characteristics of fixed-free abrasive combined wire sawing PV polycrystalline silicon solar cell
摘要： At present, the fixed abrasive wire sawing (FAWS) technology is gradually used in the photovoltaic industry to cut polycrystalline silicon slices. However, there are obvious directional wire marks, parallel grooves, and amorphous silicon layer on the surface of the slices formed by the FAWS, which leads to a high optic reflectivity of the textured surface obtained after the mature acid etching texturization technology. So the slices cannot meet the requirements of the photovoltaic cell. In the paper, a novel fixed-free abrasive combined wire sawing (FFACWS) technology for cutting PV polycrystalline silicon is presented to solve this problem, by adding loose SiC abrasives to cooling lubricant during the fixed abrasive wire sawing. A single-factor and orthogonal experimental study on sawing characteristics was carried out. The effect of size and mass fraction of SiC abrasives in the slurry, workpiece feed speed and wire speed on the surface morphology, roughness, and kerf loss were studied. The results show that within the range of the processing parameters in the paper studied, the obvious wire marks, parallel grooves, and ductile layers on the surface of the slices can be removed by the FFACWS. The surface roughness of the slices along the wire movement direction and the workpiece feed direction increases with the increase of the mass fraction of SiC abrasives in the slurry and workpiece feed speed and it decreases with the increase of wire speed. But the effect of the size of SiC abrasives is related to the matching of the protruding height of the fixed abrasives on the wire surface along the workpiece feed direction. In the wire movement direction, it increases with the size of SiC abrasives. The kerf loss increases with the increase of size and mass fraction of SiC abrasives in the slurry and the wire speed but has little effect with the change of workpiece feed speed.
关键词： Fixed-free abrasive combined wire sawing,Surface morphology,Surface roughness,Kerf loss,Photovoltaic polycrystalline silicon
更新于2025-09-23 15:19:57
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Laser polishing of 3D printed metallic components: A review on surface integrity
摘要： 3D Printing is an emerging technology to fabricate complex components in less lead time compared to traditional manufacturing processes. 3D printing enables to build metallic functional components directly from CAD model by depositing the material layer by layer. The fabricated components generally have very rough surfaces and demands for post processing, so that it can directly employ for its end use. Owing to drawbacks like time consuming, skilled labour requirement and limited scope of automation, conventional ?nishing processes ?nd less application for ?nishing freeform components. Laser Polishing is a highly productive, contactless and fully automatic post processing technique which is giving promising results to lower the surface roughness of 3D printed metallic components from the past two decades. In laser polishing, when the components are irradiated by the laser radiation, peaks of the surface are melted to a very thin layer and redistributed into the valleys by surface tension and gravity. Laser polishing has shown its ability to polishing varieties of materials from re?ective materials like aluminium to high strength materials like Inconel and Titanium alloys. In this present article, a review of laser interaction on surface integrity and mechanical properties of different materials used in metallic 3D printing are reported. The optimum process parameters of laser polishing like laser power, beam diameter, scanning speed and scan spacing/step over are also mentioned with respect to each material.
关键词： Post processing,Surface roughness,Finishing,Metallic additive manufacturing,Selective laser melting,Laser re-melting
更新于2025-09-23 15:19:57
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Study on laser annealing of niobium films deposited on copper for RF superconducting cavities
摘要： Niobium sputtered copper cavities were proposed as a kind of promising next generation superconducting cavities, but were still challenged by the Q-slope effect under high acceleration gradients. Current solutions focus on improving the film quality to make it more bulk-like, for which a higher substrate temperature is required. However, due to the limitation of the melting point of the copper substrate, both the deposition process and the post-annealing process cannot be performed at a high temperature. The laser annealing mentioned in this paper uses nanosecond pulsed laser as the heat source, and the local temperature field generated within the thickness scale of the niobium film can anneal the film without affecting copper substrate. Laser annealing system has been set up in Peking University, and experiments with niobium thin film on copper (Nb/Cu) samples have been carried out. Superconducting performance, surface topography and other properties of Nb/Cu samples before and after annealing are compared. Recrystallization of niobium films happened and various factors that may cause Q-slope have been suppressed according to the results. All these indicate the effectiveness of laser annealing and the possibility of being used in niobium sputtered copper cavities in the future.
关键词： Surface topography,Surface roughness,Recrystallization,Niobium thin film,Superconducting cavity,Laser annealing
更新于2025-09-23 15:19:57
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Investigation for Sidewall Roughness Caused Optical Scattering Loss of Silicon-on-Insulator Waveguides with Confocal Laser Scanning Microscopy
摘要： Sidewall roughness-caused optical loss of waveguides is one of the critical limitations to the proliferation of the silicon photonic integrated circuits in fiber-optic communications and optical interconnects in computers, so it is imperative to investigate the distribution characteristics of sidewall roughness and its impact upon the optical losses. In this article, we investigated the distribution properties of waveguide sidewall roughness (SWR) with the analysis for the three-dimensional (3-D) SWR of dielectric waveguides, and, then the accurate SWR measurements for silicon-on-insulator (SOI) waveguide were carried out with confocal laser scanning microscopy (CLSM). Further, we composed a theoretical/experimental combinative model of the SWR-caused optical propagation loss. Consequently, with the systematic simulations for the characteristics of optical propagation loss of SOI waveguides, the two critical points were found: (i) the sidewall roughness-caused optical loss was synchronously dependent on the correlation length and the waveguide width in addition to the SWR and (ii) the theoretical upper limit of the correlation length was the bottleneck to compressing the roughness-induced optical loss. The simulation results for the optical loss characteristics, including the differences between the TE and TM modes, were in accord with the experimental data published in the literature. The above research outcomes are very sustainable to the selection of coatings before/after the SOI waveguide fabrication.
关键词： optical scattering loss,sidewall roughness,silicon-on-insulator waveguide
更新于2025-09-23 15:19:57
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Surface and subsurface characteristics of laser polished Ti6Al4V titanium alloy
摘要： This paper aims at investigating the effects of laser power, laser pulse repetition rate and scan speed on the polished metal surface and subsurface characteristics. The influence of initial surface roughness of workpiece on the polishing performance was also taken into account. In this study, Ti6Al4V titanium alloy was selected as a specimen to be polished by a nanosecond pulse laser. The results revealed that the surface roughness was able to be improved by about 43% when the laser fluence of 1–3 J/cm2 was applied. In addition, the proper polishing condition was dependent on the initial surface roughness of workpiece, and a better surface improvement was subjected to a lower initial surface roughness. A thick recast layer, high degree of oxidation and large heat-affected zone with lots of micro-cracks were obtained when too high laser power and slow scan speed were used in the polishing of titanium alloy. With regard to the findings of this study, the suggested polishing conditions could be applied for smoothing the different levels of initial surface roughness of titanium alloy and possibly other similar metals with less subsurface damage.
关键词： Surface roughness,Polishing,Titanium alloy,Laser
更新于2025-09-23 15:19:57
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Investigation of hole quality in drilled Ti/CFRP/Ti laminates using CO2 laser
摘要： The machinability of titanium (Ti) and carbon fiber reinforced plastic (CFRP) (Ti/CFRP/Ti) laminates using CO2 laser is presented in this work. The effect of line energy and laser frequency on output responses such as heat affected zone (HAZ), taper angle (TA), metal composite interface (MCI) damage, surface roughness, dross height, and circularity were investigated. Line energy - the most influential parameter - demonstrated a threshold behavior; no drilling was observed below a certain line energy. Scanning acoustic microscopy (SAM), scanning electron microscopy (SEM), micro-computed tomography (μ-CT), and other imaging techniques were used to establish a correlation between laser parameters and CO2 laser machined damage in Ti/CFRP/Ti laminates. The results show that using a higher frequency and lower line energy can significantly improve the hole quality. However, dross free holes with minimum taper can be obtained using higher line energy.
关键词： Surface roughness,Circularity,Micro-hardness,CO2 laser,Dross height,HAZ,Drilling,Ti/CFRP/Ti,MCI damage factor,TA
更新于2025-09-23 15:19:57
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Laser surface re-melting of additive manufactured samples with a line focused beam
摘要： The laser polishing mechanism is based on the fusion of a micro layer of material due to the action of the high temperature laser beam. Laser polishing, also known as laser surface remelting, involves melting a thin layer of the substrate, with surface tension causing the material to flow from peaks to valleys. In laser polishing, the material is not removed; rather it is relocated as a molten pool. The laser beam with sufficient energy density is first allowed to quickly fuse a layer on the substrate surface of microscopic thickness. Accordingly, the peaks of the asperities on the substrate surface are fused. Owing to the fluidity of this molten metal, it easily flows into the adjacent valleys of the asperities on the surface. The same molten layer is then allowed to re-solidify so that solidified layer remains adhered to the substrate surface. This, in turn, diminishes the peaks and valleys of the asperities, which ultimately results in a smoother surface. Since surface roughness is one major limitation of additive manufacturing components, so this article makes an attempt to address the roughness of such components. The capability of laser polishing (or laser surface remelting) in reducing surface roughness is explored for various beam power and scan speed. The better set of parameters for this purpose are presented. A final surface roughness in the range of 1.0–1.1 lm is obtained for three different set of parameters. 85% reduction in surface roughness due to laser polishing is also observed.
关键词： Cylindrical lens,Laser polishing,Surface roughness,Additive manufacturing,Laser surface remelting
更新于2025-09-23 15:19:57
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Top-hat and Gaussian laser beam smoothing of ground fused silica surface
摘要： Laser smoothing is a promising technique for processing optical glass due non-contact characteristics and easy-adaptability to non-spherical surfaces. The smoothing effects of CO2 laser of top-hat and Gaussian intensity on ground fused silica surfaces were examined in the work. The results show that ground surface with surface micro-roughness of 500 nm (RMS) can be smoothed to < 0.5 nm (RMS) with both intensity profiles. Best surface roughness rises with increasing power density of laser and therefore lower power density combined with slow scanning speed is favored to improve surface quality. Numerical model was established to investigate thermal and hydrodynamic transient process to elucidate the underlying mechanism. Simulations show that smoothing process takes place at the same time as the temperature rises due to ever-decreasing viscosity of fused silica. Beam shaping is able to reduce peak power density of high power processing laser and smoothing efficiency might be increased without the loss of the processed quality of glass.
关键词： Laser smoothing,Roughness,Top-hat beam,Gaussian beam,Fused silica,Laser polishing
更新于2025-09-23 15:19:57