We compare different pulse durations, modes and repetition rates of infrared ultrashort pulses lasers for the inscription of printed electronics sensors under 100 μm scale. We investigate pulse widths varying from 200 fs up to 10 ps, and standard single pulse versus 5 GHz burst regimes to produce the most efficient and cleanest ablation. The aim of the investigated process is to ablate a layer of conductive material like carbon, NiAl or NiCr forming the electronic track contours, without damaging the support which is made of a dielectric insulator. Depending on the materials and substrates of the printed electronics circuits, we have observed that 10 ps pulses in GHz burst regime with moderate individual pulse energy (around 10 μJ) have a lot of potential for an efficient production.
Ultra-short pulse laser machining has been applied to the polishing of polycrystalline diamond (PCD) wafers in order to generate a smooth surface finish and reduce mechanical polishing time. Past studies were first carried out with a 5W laser highlighting the difference in ablation rates between PCD grades and the possible graphitization of diamond on the surface of micrometric PCD grades over a fluence threshold. Some upscaling work was undertaken at 80W with a 3-pulse burst reducing the Sa of a micrometric PCD grade lapped surface by 50% with a volume removal rate double that of the conventional mechanical polishing technique. From these previous base investigations, an ultra-short pulse laser delivering an average power of 1kW at 500fs via state-of-the-art thin disk multi-pass amplification is implemented here to achieve a higher ablation rate for high throughput processing. This is the first time that such an average power is applied on polycrystalline diamond in the ultra-short pulse regime. A burst mode is also implemented which is demonstrated to reduce the Sa by 10% and 55% on fine and coarse grade surfaces respectively compared to single pulse processing. From 80W to 1kW, the ablation rate is increased by a factor of 70 on micrometric PCD grades while the Sa of the initial lapped surface is reduced by 14% without any graphitization of the diamond structure. However, no improvement of the Sa is performed on the initial surface of coarser grades due to the formation of cavities (~5μm wide) potentially caused by the spallation of diamond grains.
The recent development of Ultra Short Pulse lasers has widely broadened the range of possibilities of laser material processing. Associated with a proper beam splitting it enables adding to the surface new properties by texturing it.
We present here a fully reflective three by three beam splitter compatible with high power up to 300W with 500fs pulses lasers. The process results are presented including the repeatability of the pattern, and the achievable ablation rate. The pattern is 15µm waist gaussian beams with 300µm pitch.
Compatibility with scanning system and F-theta lenses, enabling micro-processing throughput improvement, is described.
The advantages of the femtosecond laser for micromachining of materials have been widely demonstrated allowing the laser micromachining to reach a level of accuracy in the micrometer range level. However, most of the current femtosecond laser micromachining applications are for flat surfaces, 2D or 2.5D, requiring different kinds of machining: drilling, cutting, and texturing, for more and more exotic materials. Biomedical implants are a part of those new objects requiring very high level of accuracy and surface finish, and for complex geometries: cylindrical or hemispherical shapes. LASEA has developed a system combining femtosecond laser with 7 simultaneously moving axes: 5 mechanical axes and 2 galvanometric axes. This combines the 3D micromachining offered by the 5 axes with the fast scanning. The laser parameters and strategies are controlled owing to laser specific developed functionalities. Another challenge to overcome is the research of laser parameters which is time and material consuming. In order to make this research more efficient, LASEA has developed a tool named LS-Plume which simulates the profiles for different sets of parameters.
In this work, we focus mainly onto biomedical implants, such as stent cutting and hip implants texturing. The characterisation of the stents was carried out based on computed X-ray tomography, after processing and balloon inflation. Fast texturing of 3D part is also demonstrated and evaluated. Different biocompatible materials have been characterised and used by the tool LS-Plume. Showing a good match between a simulated and measured profiles.
Ablation by ultrafast lasers results from a series of complex nonlinear phenomena of absorption and transfer of energy that take place in the surfaces of materials upon irradiation. Provided that a good window of processing parameters is chosen, the resulting thermal effects are in general negligible, making ultrafast lasers excellent micromachining tools applicable to most types of materials. It is thus beneficial to understand how ablation is affected by the laser processing parameters and the material properties, in order to optimize the micromachining processes.
We propose an engineering model to estimate the dimensions of ablation, taking into account on the one hand the material properties such as the ablation threshold, penetration depth and the refractive index and, on the other hand, the processing parameters namely the pulse energy and beam diameter, scanning speed, repetition rate and angle of incidence. The model considers as well the effects of incubation, changes of topography during multi-pulse irradiation, surface reflectivity and Gaussian beam diameter variation with the distance to the focal plane.
The model is able to simulate the profiles of ablation surfaces produced by normal or tilted laser beam, either for spot, line and area processing. The results obtained are validated by comparison to the ones obtained experimentally. Both the model and the experiments focus on stainless steel. The predictions of the model also allow for the optimization of the micromachining process, both energy and time wise.
The today available ultra-short pulsed laser systems offer average power in the range of 100 W or even more resulting in high pulse energies. In contrast to treat metals only moderate peak fluences are required to work at the well-known optimum point, where the ablation process is most energy efficient. In a standard setup the laser beam is deflected by a galvo scanner. The achievable scan speed is limited and therefore also the usable repetition frequency and average power. The use of pulse bursts instead of single pulses is a possibility to further increase the ablation rate, i.e. using higher average power. This further increase is crucial for the usage of the ultra-short pulses in industrial applications. It was shown in previous publications that the number of pulses in the burst have a significant influence on the specific removal rate in case of ps pulses. It was observed, that the second pulse of a 2-pulse burst is shielded by the particle plume of the first pulse of the burst. It is believed that the shielding effect depends on the particle density of the plume, thus the effect should be stronger if more material is ablated. As already known, a decrease of the pulse duration to a few hundreds of fs leads to an increase of the specific removal rate for single pulses. In this work we investigate the influence of pulse bursts on the specific removal rate as well as the pulse duration on the ablation process using pulse bursts.
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