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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) - Achievement of Very Smooth Cavity Sidewalls by UV Picosecond Laser Micromachining
摘要： Achievement of very smooth cavity sidewalls by UV picosecond laser micromachining. As a contactless and maskless method generating a reduced heat affected zone compared to nanosecond laser, ultrafast laser micromachining is widely used for rapid prototyping and materials processing. Today, most research and development works is devoted to study and control LIPPS occurring at the surface of the cavity bottom. But for many applications, there is a strong need to produce highly smooth sidewalls like for microelectronic sample preparation, microfluidics, waveguides, etc.. A laser based technology allowing to obtain very smooth surfaces (Ra of ~3 nm) already exists but it involves melting of a significant volume of material. So far, to the best of our knowledge, no parametric study aiming at minimizing the roughness of picosecond laser micromachined sidewalls in silicon has been performed. In the present work, picosecond laser micromachining (532 nm and 343 nm) of cavity sidewalls in silicon is studied. The evolution of the surface roughness is deeply investigated experimentally and theoretically as a function of laser and scanning parameters. We demonstrate that RaX, which is measured along the scanning laser beam direction, can be minimized by increasing laser beam overlap and the crater size, in accordance with a simple geometrical model. Experimentally, the minimum RaX is obtained for a beam overlap of ~80% and the largest crater sizes. Beyond 80%, we observed a roughness degradation which is probably due to two main phenomena. The first involves the interaction between the laser beam and the debris, which deteriorates the beam quality. The second is related to the highly heterogeneous ablation occurring for large overlaps, which induces a rough surface. Along the beam propagation direction, the sidewall is characterized by a relatively high waviness which induces a more important height variation than the roughness. The waviness depends mainly on the Rayleigh length. Thus, it can be reduced by using a large focal spot radius and a short wavelength. Once the sidewall is finished, the surface topology does not vary much with the laser micromachining time. Overall, smooth and homogeneous surfaces can be produced by choosing a beam overlap close to 80%. The best results were obtained at 343 nm, which allows to extend the Rayleigh zone, to increase the laser absorption on the sidewall asperities and to improve the induced cleaning thanks to a more confined interaction. The present work demonstrates that very low roughness (< 40 nm) can be achieved on sidewalls of cavities by picosecond laser micromachining. In addition this approach allows the roughness tuning. As it is based on a geometrical model, it is extendable to other materials as long as the surface melting, which may erase the induced periodic structuring, is not significant. This tuning possibility can be useful to modify the surface properties, such as reflectivity, friction and wettability, and therefore adapt the sidewall to different applications.
关键词： smooth cavity sidewalls,waviness,silicon,UV picosecond laser,roughness,micromachining,Rayleigh length
更新于2025-09-12 10:27:22
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Laser metal deposition of Ti-6Al-4V alloy with beam oscillation
摘要： One of the most prevalent problems of additive technologies is the improvement of process efficiency at the expense of increase in mass deposition rate and reduction of postprocessing time. Deposition rate can be improved by the modification of the shape and size of the molten pool through the optimization of laser beam power distribution. Time and cost of postprocessing depend on the surface roughness requirements and presence of macroscopic waviness. Beam oscillation can help to solve this problem. Laser metal deposition with linear beam oscillation was studied. Effects of numerous process parameters on pool shape and size was analysed by simulation. The heat conduction problem was solved analytically by Green’s function method. Temperature fields due to moving normally distributed strip heat sources were studied. It was established that on increasing the oscillation amplitude up to laser beam radius the heat flux of normally distributed strip heat source decrease rapidly to 53%. Greater the beam radius, the less effect of amplitude on the peak value of molten pool width and lower allowable oscillation amplitude. Microscopic examination revealed that beam oscillation promotes obtaining smooth wall surface without any macroscopic waviness.
关键词： surface waviness,titanium alloy,beam oscillation,temperature field,laser metal deposition
更新于2025-09-12 10:27:22