- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Development of a predictive capability of short-pulse laser-driven broadband x-ray radiography
摘要： High intensity, short-pulse laser interaction with a solid metal target produces broadband hard x rays potentially for various applications of x-ray radiography. Here experimental benchmarking of numerical modelling for short-pulse laser-driven broadband x-ray radiography is presented. Angular dependent x-ray spectra are first calculated with a hybrid particle-in-cell code, Large Scale Plasma (LSP), using fast electron parameters inferred from an analysis of measured bremsstrahlung signals. Subsequently, a calculated x-ray spectrum in the direction of radiography is used in photon transport calculations using a Monte Carlo code, Particle and Heavy Ion Transport code System (PHITS), to simulate a radiographic image including a modelled 3D test object, an x-ray attenuation filter and an image plate detector. Simulated radiographic images are compared with measurements obtained in an experiment using a 50-TW Leopard short-pulse laser at the University of Nevada Reno. Results show that simulations reproduce the experimental images well for three different attenuation filters (plastic, aluminium, and brass), while one-dimensional transmission profiles for the plastic and aluminium filters are quantitatively in good agreement. The modelling approach established in this work could be used as a predictive tool to simulate radiographic images of complex 3D solid objects at any arbitrary angular position or to optimize experimental components such as the source spectrum, x-ray attenuation filters and a detector type depending on a radiographic object without carrying out radiographic experiments.
关键词： Monte Carlo simulations,hybrid particle-in-cell,broadband x-ray radiography,short-pulse laser-produced x rays
更新于2025-09-23 15:21:01
-
Time-fractional subdiffusion model for thin metal films under femtosecond laser pulses based on Caputo fractional derivative to examine anomalous diffusion process
摘要： In this paper, the non-Fourier effects are examined in thin metal films exposed to femtosecond laser pulses. For the first time, the time-fractional subdiffusion model is presented based on the Caputo fractional derivative to examine the anomalous diffusion process in nano-scale metal films. The fractional heat conduction equation is solved numerically, using the finite difference method based on implicit scheme and the numerical results are compared to experimental data. The comparison implies that the numerical results well coincide with experimental data, proving the accuracy and suitability of fractional model to capture thermal behaviors of thin metal films heated by short-pulse laser. Furthermore, the results of time-fractional model are compared to other models including parabolic and hyperbolic two-step models. Having compared, one can be found is that the fractional model is more reliable than other models, because its results are well matched with experimental data. The use of Fourier’s law in parabolic and hyperbolic two-step model leads to deviation from experimental data which can be addressed upon applying the proposed time-fractional model in this work. Moreover, the presented time-fractional model can be effectively utilized for studying the heat transport in thin metal films under laser pulses as well as the laser heating process and its applications in engineering. Ultimately, the effect of changes in various parameters such as order of fractional derivative, laser pulse duration, metal materials (gold and chromium), gold film thickness, relaxation time and absorption depth of laser pulses are investigated on temperature response of thin metal films.
关键词： Time-fractional subdiffusion model,Short-pulse laser,Thin metal films,Caputo fractional derivative
更新于2025-09-23 15:19:57
-
The implementation and data analysis of an interferometer for intense short pulse laser experiments
摘要： We present an interferometry setup and the detailed fringe analysis method for intense short pulse (SP) laser experiments. The interferometry scheme was re?ned through multiple campaigns to investigate the effects of pre-plasmas on energetic electrons at the Jupiter Laser Facility at Lawrence Livermore National Laboratory. The interferometer used a frequency doubled (λ = 0.527 μm) 0.5 ps long optical probe beam to measure the pre-plasma density, an invaluable parameter to better understand how varying pre-plasma conditions affect the characteristics of the energetic electrons. The hardware of the diagnostic, data analysis and example data are presented. The diagnostic setup and the analysis procedure can be employed for any other SP laser experiments and interferograms, respectively.
关键词： short pulse laser,optical interferometry,Mach–Zehnder interferometer,picosecond probe,plasma density
更新于2025-09-19 17:13:59
-
Femtosecond Pulsed Laser Deposition of Chromium Diboride-Rich Thin Films
摘要： Chromium borides are promising candidates for several structural applications including protective coatings for materials exposed to corrosive and abrasive environments. In this paper the pulsed laser deposition of chromium diboride-rich thin ?lms has been carried out in vacuum by using a frequency doubled Nd:glass laser with a pulse duration of 250 fs. The ?lms have been deposited at di?erent substrate temperatures and characterized by X-ray di?raction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Lastly, the ?lm’s hardness has been studied by Vickers indentation technique. The results indicate that only the ?lms deposited at a substrate temperature of 500 C are crystalline and formed by chromium diboride, together with a certain amount of boron and chromium, which suggests that, as main mechanism, a process taking place on the surface from atoms and ions from the gas phase. This hypothesis has been con?rmed by the study of the plasma produced by the ablation process.
关键词： thin ?lms,pulsed laser deposition,chromium diboride,ultra-short pulse laser
更新于2025-09-16 10:30:52
-
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
-
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
-
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
-
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