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The laser-based time calibration system for the MEG II pixelated Timing Counter
摘要： We have developed a new laser-based time calibration system for highly segmented scintillator counters like the MEG II pixelated Timing Counter (pTC), consisting of 512 centimetre-scale scintillator counters read out by silicon photomultipliers (SiPMs). It is difficult to apply previous laser-based calibration methods for conventional metre-scale Time-Of-Flight detectors to the MEG II pTC from the implementation and the accuracy points of view. This paper presents a new laser-based time calibration system which can overcome such difficulties. A laser pulse is split into each scintillator counter via several optical components so that we can directly measure the time offset of each counter relative to the laser-emitted time. We carefully tested all the components and procedures prior to the actual operation. The laser system was installed into the pTC and thoroughly tested under the real experimental condition. The system showed good stability and being sensitive to any change of timing larger than ～10 ps. Moreover, it showed an uncertainty of 48 ps in the determination of the time offsets, which meets our requirements. The new method provides an example of the implementation of a precise timing alignment for the new type of detectors enabled by the advance of SiPM technology.
关键词： Pulse laser,Scintillator counter,SiPMs,Time calibration
更新于2025-09-16 10:30:52
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Study on nonthermala??thermal processing boundary in drilling of ceramics using ultrashort pulse laser system with variable parameters over a wide range
摘要： Quality and throughput of laser material processing are influenced by multiple laser parameters as well as material properties. Since material degradation due to laser processing is generally related to heat-affected zone, quick optimization and realization of nonthermal process is one of the most important issues for higher-grade laser processing. In this work, we developed various parameter-controlled ultrashort pulse laser system that can control various laser parameters over a wide range, such as pulse duration over three orders of magnitude. Using this laser system (wavelength: 1033 nm, pulse duration: 0.4 to 400 ps, repetition: up to 1 MHz), we have investigated nonthermal–thermal processing boundary in drilling of ceramics: aluminum nitride (AlN) and yttria-stabilized zirconia (YSZ), with high and low thermal conductivity, respectively. As a result, the AlN ceramic exhibited strong dependence of ablation rate on fluence: low-, mid- and high-fluence regimes appeared with different logarithmic correlations. Further, the nonthermal–thermal process boundaries appeared, depending on the pulse duration. On the other hand, the ablation behavior of YSZ was much different from AlN; the ablation rate did not show distinct three regimes. Further, there were no nonthermal process windows for the YSZ. Therefore, the nonthermal–thermal process boundaries were governed by the laser parameters like pulse duration as well as the material thermal conductivity.
关键词： Ultrashort pulse laser,Ceramics,Drilling
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) - Controllable Generation of Ultrashort Multi-Bound Solitons in a Mode-Locked Erbium-Doped Ring Laser with a Highly-Nonlinear Resonator
摘要： Mode-locked (ML) ultrashort pulse (USP) fiber lasers can be treated as an ideal platform to expand future applications due to a complex nonlinear dynamics with a presence of a high value of a group velocity dispersion and a third-order dispersion in the laser resonator. Up to now a series of novel ML regimes have been investigated e.g. self-similar pulses, noise-like pulses, multi-bound solitons, and a soliton rain generation. Multi-bound solitons (MBS) generation regime, also known as soliton molecules, is of considerable interest in various fields of applications. For example, the investigation of a MBS generation is very attractive for increasing the data transfer capacity in telecommunications due to coding alphabet extension. The coding concept of MBS suggests a data stream using more than two symbols (2?N symbols, where N is the number of generated solitons in a bound state) [1]. And also, recent research shows that using ultrafast bursts of pulses can improve the quality of laser ablation for medical applications [2]. Moreover, MBS generation can be also used in a coherent pulse staking amplification scheme increasing an amplification efficiency along with a formation of high-energy solitons at a high-repetition-rate [3]. Previously we have obtained a generation of stable low-noise ultrashort multi-bound solitons in a passive mode-locked all-fiber erbium-doped ring laser with a highly-nonlinear resonator [4]. Fig. 1 shows autocorrelation traces and spectrums of MBS generation obtained by pump power variation at a wavelength of 980 nm. The output spectrums are evidently showing high-contrast intensity fringes (up to ~20 dB) and autocorrelation traces having symmetrical form without additional intensity peaks that indicates a stable and strong coherent connection between ultrashort pulses and fixed coherent phase difference in the temporal domain between several identical pulses. It is known that the highest energy of a fundamental soliton in a laser resonator with duration τp is limited by the soliton area theorem Es ~ |β2|/(γ · τp), where γ is the net nonlinear coefficient and β2 is the total cavity dispersion [1]. Soliton energy quantization results in pulse splitting at operation powers higher than the fundamental limit. Here we experimentally demonstrate the formation multi-bound solitons with the controllable number of bound states 7 < N < 17 by pump power variation in the range from ~160 mW to ~377 mW obtained in a highly-nonlinear fiber ring cavity.
关键词： ultrashort pulse,laser ablation,fiber lasers,Mode-locked,coherent pulse staking amplification,soliton molecules,telecommunications,multi-bound solitons
更新于2025-09-12 10:27:22
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Implementation of a phase plate for the generation of homogeneous focal-spot intensity distributions at the high-energy short-pulse laser facility PHELIX
摘要： We propose and demonstrate the use of random phase plates (RPPs) for high-energy sub-picosecond lasers. Contrarily to previous work related to nanosecond lasers, an RPP poses technical challenges with ultrashort-pulse lasers. Here, we implement the RPP near the beginning of the ampli?er and image-relay it throughout the laser ampli?er. With this, we obtain a uniform intensity distribution in the focus over an area 1600 times the diffraction limit. This method shows no signi?cant drawbacks for the laser and it has been implemented at the PHELIX laser facility where it is now available for users.
关键词： high-power laser,phase plate,short-pulse laser,beam shaping
更新于2025-09-12 10:27:22
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Ablation Investigation of Cemented Carbides Using Short-Pulse Laser Beams
摘要： As an excellent engineering tool material, cemented carbides are capable to shape and cut metallic materials with high surface finish quality and precision. However, in regard to conventional abrasive methods cemented carbides are difficult-to-machine materials due to their extreme hardness combined with relatively low toughness. In contrast, laser beam machining is an advanced non-contacting cutting method which is therefore suitable for shaping hard materials. In particular, the application of short-pulse laser beams enables the cutting of hard materials meeting high precision requirements. Moreover, it can effectively reduce defects induced by mechanical contacts and thermal reactions. In this paper, a general study of the ablation mechanism of cemented carbides using short-pulse laser is conducted. Special attention is paid to the correlation between the material ablation and machining parameters within the nanosecond regime: pulse number and pulse energy. In doing so, two cemented carbide grades with similar composition but different grain size have been chosen as investigated materials. An experimental set-up equipped with a nanosecond laser and an auto-stage is implemented to produce dimples on the cemented carbide surfaces with variable pulse number and pulse energy. The experimental design and characterization of geometrical features of produced dimples are presented and discussed. The work is complemented with a thorough surface integrity assessment of the shaped materials. It is found that ablation increases proportionally with the pulse number and applied energy. Regarding microstructural effects, ablation is discerned to be more pronounced in the coarse-grained grade as compared to the medium-sized one.
关键词： laser beam machining,short-pulse laser,surface integrity,cemented carbides
更新于2025-09-12 10:27:22
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Fabrication of a ball end nose micro milling tool by tangential laser ablation
摘要： The general trend towards miniaturization of components is leading to an increasing demand for micro cutting tools. Such tools are found in a variety of applications like optics manufacturing, mold machining or medical technology. Indeed, micromachining exhibits a high efficiency, accuracy and low cost in comparison to other micro processing technologies. Micro cutting tools are mostly produced by grinding, a mechanical process, which might damage the tool due to induced forces, vibrations and heat. These detrimental effects cause the high scrap rate in the manufacturing of micro cutting tools and limited geometrical flexibility. A new approach for the manufacturing of micro cutting tools is given by the ultrashort-pulsed laser technology: it enables material removal, which is independent of the hardness of the workpiece material and with only a negligible heat-affected zone. In most cases, laser ablation is disadvantaged in contrast to grinding because of its relatively low material-removal rate. When it comes to the manufacturing of micro cutting tools the small amount of material to be removed makes the ultra-short pulsed laser an interesting alternative to grinding. Furthermore, the laser ablation is a force and wear-free process, which ensures high precision. In this paper, a commercially available micro ball end mill geometry is measured by micro X-ray tomography and 3D microscopy. The movement of the mechanical axes and the path of the laser beam for manufacturing the desired tool are determined based on these measurements. The milling tools with a diameter of 100 μm are produced from cemented carbide blanks, on a 8-axis laser machining center. After machining, the tools are analyzed by SEM and using FIB: By creating a cross section perpendicular to the cutting edge the heat-affected zone is examined. Finally, the cutting tool is successfully applied for the manufacturing of micro electrodes in copper for an EDM process while recording the cutting forces.
关键词： ultrashort pulse laser ablation,tangential laser ablation,ball end nose micro milling tool
更新于2025-09-12 10:27:22
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A Model for Predicting the Geometry of Crater on Grinding Wheel Surface Ablated with a Single Pulsed Laser
摘要： In this paper, a three dimensional transient heat transfer model for predicting the 3D geometry of crater and its cross sectional profile on grinding wheel surface ablated by a single pulsed Nd: YAG laser is covered. The model considers the heterogeneity of wheel structure, the variation of energy in a pulsed laser input to the wheel, heat transfer by conduction, convection, radiation and the thermo-physical and optical properties of bond and grit while predicting the temperature distribution in the irradiated region using COMSOL Multiphysics? 5.2 package. From this temperature distribution, the shape of crater was predicted. Crater depth predicted was validated with the published results confirming the suitability of this model for predicting the shape of crater in single pulsed laser ablation of wheel surface. Post modeling analysis gives insights of the process mechanism of laser dressing and the parameters affecting the crater geometry. Future scope and implementation of this model is discussed in detail.
关键词： single-pulse laser ablation,laser dressing of grinding wheels,wheel structure model,crater geometry
更新于2025-09-12 10:27:22
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Microstructural and Metallurgical Assessment of the Laser-Patterned Cemented Tungsten Carbide (WC-CoNi)
摘要： Cemented carbide is difficult to machine using traditional chip-removal methods due to its hardness. Electrical discharge machining (EDM) is the common method applied to shape cemented carbides because high geometric precision can be achieved. However, some important defects (pores, residual stresses or oxidation products) can be induced due to thermal reactions. Ultra-short pulse laser processing can also provide high precision and meanwhile effectively avoid these defects due to its short laser-matter reaction time. In this paper, three different patterns on WC-CoNi cemented carbides for tribological purposes, namely line-like patterns, dimples and grooves, have been created using different laser set-ups with pulse duration in the range of nanoseconds (10-9s), picoseconds (10-12s) and femtoseconds (10-15s). Microstructural and metallurgical changes of modified surfaces have been studied. Laser scanning microscopy (LSM) is conducted to measure the pattern dimensions. Focused ion beam (FIB) in combination with scanning electron microscope (SEM) is used to investigate the microstructural changes of the patterned materials.
关键词： Surface integrity,Laser surface patterning (LST),Cemented carbide,Ultra-short pulse laser processing
更新于2025-09-12 10:27:22
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[IEEE 2018 Progress in Electromagnetics Research Symposium (PIERS-Toyama) - Toyama (2018.8.1-2018.8.4)] 2018 Progress in Electromagnetics Research Symposium (PIERS-Toyama) - A Chip of Pulse-Laser-Assisted Dual-Beam Fiber-Optic Trap
摘要： Compared with the single-beam gradient optical trap, the dual-beam optical trap based on micro-structure eliminates the need for complex optical alignment and offers intrinsic benefits of miniaturization and stabilization, which are crucial for developing a practical sensor. We design a monolithic chip of dual-beam fiber-optic trap which allows extremely accurate alignment of submicron scale between two counter-propagating fiber beams. Based on micromachining technology, the chip featured a V-shaped groove to align the fibers and a rectangular channel to load the particles is experimentally realized. Recent studies have demonstrated that micro-scale particles can be removed effectively from substrate by focused pulse laser beam. To acquire high trapping efficiency and better trapping stability, we propose a new loading method that combinates pulse laser with dual-beam fiber-optic trap. We have fabricated a silica miniature operating rod for initial storage of the microspheres and moved a targeted particle into the effective trapping area of the fiber-optic trap. Optical loading and trapping of a 10 μm polystyrene particle in air are demonstrated and the controllable capturing process avoids any contamination on fiber ends, which ensures the reliability of optical path. We use a microscopic imaging system and image processing method to test the static stability of the captured particle. The static stability of the microspheres is submicron, which is clearly superior to the test results in liquid environment. The rapid loading and manipulation of microspheres in optical trap is significant for its applications in optomechanics and precision force sensing. Our results pave the way for a new class of monolithic and portable optical sensor for inertial measurement.
关键词： micromachining,fiber-optic trap,optical sensor,dual-beam optical trap,pulse laser
更新于2025-09-12 10:27:22
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An industry-relevant method to determine material-specific parameters for ultra-short pulsed laser ablation of cemented carbide
摘要： In recent years, it has been shown that ultra-short pulsed lasers can be used for the post processing and the fabrication of cutting tools. This new manufacturing technology can compete with the mainly used grinding process due to its ability to ablate materials independent of their hardness and without any wear. The knowledge of material properties is necessary for an optimal choice of machining parameters and the prediction of the ablation process. Measuring them is challenging, especially for inhomogeneous, ultra-hard materials. In this paper, an industry-relevant method is presented, which enables to determine the threshold fluence and the optical properties of cemented carbide. The required material-specific parameters are derived from simple ablation experiments, which are carried out on a modern laser machining center. Finally, the results are used to present a formula to calculate the material removal rate at different angles of incidence of the laser beam.
关键词： Neuenschwander model,ultra-short pulse laser machining,ablation efficiency,inclined incidence,threshold fluence,ablation rate,cemented carbide
更新于2025-09-12 10:27:22