LASER MICRO PROCESSING USING A HIGH REPETITION RATE FEMTO SECOND LASER (original) (raw)
Related papers
2011
The paper presents a study of laser micro processing of metals by using a high repetition rate femto second laser. On stainless steel (AISI 304), copper and aluminium the impact of the significant laser processing parameters onto the machining process was investigated, such as laser fluence, repetition rate, lateral pulse distance and polarisation. The machining results were evaluated by the ablation rate, surface roughness, process efficiency, material removal rate and the wall-angle. For complementary discussions the experimental data were compared with results achieved in theoretical analysis. Outgoing from the results appropriate laser processing parameters were derived in order to optimise the machining process. With the application of ultra short laser pulses highquality machining results with a minimal thermal load and a roughness R a of the laser processed surface of only some hundreds nano meter were obtained. On other hand high machining throughputs were achieved due to application of high repetition rates. Finally, the possibilities and the limits of the high repetition rate femto second laser technology in laser micro processing are demonstrated by means of threedimensional micro structured machining examples.
Micro structuring with highly repetitive ultra short laser pulses
For the first time an industrial high repetition ultra short laser source with pulse lengths less than 250fs, high beam quality M² better than 1.2, high pulse energies up to 8µJ, and repetition rates up to 25MHz (IMPULSE, Clark-MXR, Inc.) is applied for micro material processing. First results of stainless steel machining are presented to demonstrate the possibilities and limits of the machining process with high repetition laser pulses. Because of relatively high pulse energies at high pulse repetition rates completely new effects of laser material interaction are obtained. Principle mechanisms of heat accumulation and plasma or particle shielding processes are derived from experimental results, and models are discussed. Finally, formation of self organized laser induced micro structures is shown and the influence of machining parameters is presented.
Processing of metals and semiconductors by a femtosecond laser-based microfabrication system
Commercial and Biomedical Applications of Ultrafast Lasers III, 2003
A microfabrication system with the use of a femtosecond laser was designed for 3D processing of industrially important materials. The system includes a 120 fs, 1 kHz laser; beam delivery and focusing system, systems for automated 3D target motion and real-time imaging of the sample placed in a vacuum chamber. The first tests of the system on the processing of stainless steel and silicon are presented. We established thresholds and regimes of ablation for both materials. It was found that at relatively low laser fluences I < 3-5 J/cm 2 the regime of "gentle" ablation takes place, which is characterized by exceptional quality of the ablated surface, but slow ablation rate (< 25 nm/pulse). This regime is especially efficient for the patterning of markers on steel or silicon surfaces. The "fast" ablation regime at I > 10 J/cm 2 provides much higher ablation rate of 30-100 nm/pulse, giving an opportunity of fast high-quality processing of materials. This regime is well suited for drilling of through holes and fast cutting of materials. However, it was found that fast ablation regime imposes additional requirements on the quality of delivery and focusing of the laser beam because of the presence of parasitic ablation around the main spot on the tail of the radiation intensity distribution. As industrial machining examples, we demonstrate heat-affected-zone free drilling of through holes in a 50 µm thick stainless steel foil and and cutting of a 50 µm thick Si wafer with a net cutting speed of 8 µm/sec.
Femtosecond Laser Micro/nano Machining on Metallic and Semiconductor Materials
Formation of ripples or laser induced periodic surface structures (LIPSS) on semiconductor material like Silicon (Si) and on metals like Aluminum (Al) and Copper (Cu) and fabrication Silver (Ag) nanostructures in polymer matrix by femtosecond (fs) laser direct writing are reported in this paper. Laser irradiation was performed at normal incidence in air using linearly polarized Ti:Sapphire fs laser pulses of ~ 110 fs pulse duration and ~ 800 nm wavelength. Field emission scanning electron microscopy (FESEM) is utilized for imaging surface morphologies of laser written structures, revealing that surface morphology depends on various material processing parameters like laser fluence, polarization, material properties and number of applied pulses. Formation of polymer capped Ag nanoparticles inside the laser written microstructures is confirmed by the appearance of surface plasmon absorption band at 448 nm in the UV-Vis extinction spectrum. Nanoparticles formed were spherical in shape with an average particle size less than 20 nm. This technique is efficient, universal, cost-effective, and environmental friendly, which has potential applications in the fabrication of micro/nanostructures on variety of materials for microelectromechanical systems, nanoelectronics and nanophotonics.
Applied Physics A
Ablation with ultrashort laser pulses as a surface micromachining tool was studied using a hybrid die-excimer laser system that has high energy per laser pulse (tens of mJ’s), about 600 fs pulse duration and low repetition rate (2 Hz). The effect of ablation on the material microstructure with this high energy pulsed laser system was studied. Micropillars were fabricated by laser ablation using a spot size of hundreds of micrometers. Two methods were tested for micromachining. Multiple laser pulse ablation on a standing sample resulted in a columnar microscturcure around the micropillars. This unwanted structure was avoided by beam scanning, resulting in a rather homogeneous ditch. By HR-EBSD measurement it was found that the heat affected zone is less than 1 \mu \textrm{m}$$ μ m , which was confirmed by numerical temperature simulations, too. The dislocation density measured below the specimen surface was unaltered, meaning that no significant crystal degradation occurred. In sum...
Fabrication of Micro/Nano Structures on Metals by Femtosecond Laser Micromachining
2014
Femtosecond laser micromachining has emerged in recent years as a new technique for micro/nano structure fabrication because of its applicability to virtually all kinds of materials in an easy one-step process that is scalable. In the past, much research on femtosecond laser micromachining was carried out to understand the complex ablation mechanism, whereas recent works are mostly concerned with the fabrication of surface structures because of their numerous possible applications. The state-of-the-art knowledge on the fabrication of these structures on metals with direct femtosecond laser micromachining is reviewed in this article. The effect of various parameters, such as fluence, number of pulses, laser beam polarization, wavelength, incident angle, scan velocity, number of scans, and environment, on the formation of different structures is discussed in detail wherever possible. Furthermore, a guideline for surface structures optimization is provided. The authors’ experimental work on laser-inscribed regular pattern fabrication is presented to give a complete picture of micromachining processes. Finally, possible applications of laser-machined surface structures in different fields are briefly reviewed.
Features of metal surface structuring by high-power femtosecond laser pulses
Technical Physics Letters, 2015
As is known, the interaction of a high power ultrashort laser radiation with the surface of a solid can lead to electron emission [1], the occurrence of sur face electromagnetic waves (SEMWs) , and abla tion and structuring of the surface of materials . The fundamental importance of these processes and the application potential of the results obtained have stimulated a great number of studies in this area . Laser micro and nanostructuring of the surface of dif ferent materials [2] can be implemented owing to the effects caused by generation of SEMWs at the interface between materials, which can interfere with the pri mary radiation and lead to the formation of periodic and disordered surface structures . In this case, sub melting, ablation, and surface structure variation, i.e., the formation of microrelief, can be observed in the irradiated area . These effects may underlie a variety of applications in microsensors, nanophotonic devices, and nanotechnology; in addition, they are of great fundamental importance.
Femtosecond laser micro-structuring of aluminium under helium
Applied Surface Science, 2004
The interaction of 180 fs, 775 nm laser pulses with aluminium under a flowing stream of helium at ambient pressure have been used to study the material re-deposition, ablation rate and residual surface roughness. Threshold fluence F th $ 0:4 J cm À2 and the volume ablation rate was measured to be 30 < V < 450 mm 3 per pulse in the fluence range 1:4 < F < 21 J cm À2 . The presence of helium avoids gas breakdown above the substrate and leads to improved surface micro-structure by minimising surface oxidation and debris re-deposition. At 1 kHz rep. rate, with fluence F > 7 J cm À2 and >85 W cm À2 average power density, residual thermal effects result in melt and debris formation producing poor surface micro-structure. On the contrary, surface micro-machining at low fluence F $ 1:4 J cm À2 with low power density, 3WcmAˋ2producesmuchsuperiorsurfacemicro−structuringwithminimummeltandmeasuredsurfaceroughnessRa3 W cm À2 produces much superior surface micro-structuring with minimum melt and measured surface roughness R a 3WcmAˋ2producesmuchsuperiorsurfacemicro−structuringwithminimummeltandmeasuredsurfaceroughnessRa 1:1 AE 0:1 mm at a depth D $ 50 mm. By varying the combination of fluence/scan speed during ultra-fast ablation of aluminium at 1 kHz rep. rate, results suggest that maintaining average scanned power density to <5 W cm À2 combined with single pulse fluence <4 J cm À2 produces near optimum microstructuring. The debris under these conditions contains pure aluminium nanoparticles carried with the helium stream. #