Surface roughness has a significant influence on the performance and appearance of components. By combining a boost laser with ultrafast beam deflection using a polygon scanner, very high processing speeds can be achieved. A 65 % improvement in surface roughness has been achieved on stainless steel, with Sa < 0.1 μm, while the gloss has increased from 130 to 366 GU. As a result, the previously matt surface became reflective, improving the appearance of the material. A real area rate of 156 cm2/s was achieved, comparable with industrial process times.

Es wurden Untersuchungen zur gezielten Erzeugung und Nutzung von Mikrostrukturen beim Micro Cladding durchgeführt. Die notwendigen Prozessbedingungen dafür wurden gefunden. Die Baurate konnte um den Faktor 5 erhöht werden. Eine weitere Skalierung der Baurate auf das Doppelte durch Erhöhung der Scangeschwindigkeit konnte ebenfalls gezeigt werden. Die gezielte Mikrostrukturierung ist geeignet, um 2,5 D Mikrostrukturen mit hohem Aspektverhältnis in hoher Geschwindigkeit zu erzeugen.

Ultrashort laser pulses offer enormous potential for precise micro structuring, especially of transparent materials [1-2]. When focusing ultrashort laser pulses into the material, the intensity in the focus volume is sufficient to induce non-linear absorption processes, which lead to structural changes in the material volume [3]. In the following study, the localized structural changes were arranged in order to produce cut surfaces for the extraction of 2.5D bodies with potential applications for example in the production of micro implants. The investigations were carried out in polylactide, a bioresorbable polymer. For this purpose, a femtosecond laser source was used which emits pulses of 200 fs pulse length at a wavelength of 1030 nm. Microscope objectives with focal lengths in the range of 12.5 mm down to 2 mm were used, which resulted in focal radius of 1.2 μm in minimum and hence extremely high intensities of about 1015W/cm2 to excite nonlinear absorption effects. Process-influencing parameters such as pulse energy, pulse distance and frequency were varied to investigate their effect on the quality of the cut-out bodies. The feasibility of the technology could be demonstrated on the basis of simple bodies.

In recent years, several applications for laser ablation of thin metal layers from the fused silica substrate side have been studied. The rear-side ablation is a highly effective ablation method for thin layer structuring and reveals a high structuring quality. Therefore, the present work dealt with the selective rear-side ablation of thin aluminum layers (10–50 nm) on fused silica with ultrashort-pulsed laser radiation (λ = 1028 nm, $$ \tau_{\text{H}} $$  = 0.2–10 ps and w0,86 = 15.2 µm). The influences of pulse duration and layer thickness on the ablation thresholds as well as the incubation coefficients were determined. For layer thicknesses of 30 and 50 nm, a decrease of the ablation threshold with increasing pulse duration was determined. Whereas, the ablation threshold remained constant for layer thicknesses of 10 and 20 nm. Different morphologies were observed depending on the process parameters. The rear-side ablation of aluminum proceeded over the melting phase and no lift-off process had taken place. In addition to experimental investigations, calculations were carried out to determine the theoretical threshold fluences. The theoretical values were compared to experimental data. With the help of these investigations, the quality of the structuring of aluminum layers can be improved.

The arrangement of nanometer-sized voids, induced by focusing intense laser radiation within transparent material can allow the generation of transparent components with dimensions in the micrometer to nanometre range due to internal contour cut and thus satisfy the progressive miniaturization of products in micro-optics and medical technologies. For further improvements in the precision of those components, a deep understanding of the involved processes during the interaction of laser radiation within the material is necessary. In this work, voids inside bulk polylactide (PLA), a bioabsorbable polymer, were generated using a femtosecond laser (λ = 1030 nm, τH = 180 fs) with single and multiple pulse irradiation. The dependence of the spot size was examined by the use of four microscope objectives with focus radii of 4.9, 3.3, 2 and 1.2 µm. For the experiments, the pulse energy and focusing depth into the material were varied. The dimensions of the voids were experimentally determined as function of the intensity. Differences in the lateral and axial extents of the voids were obtained for different focus radii and focusing depths at same intensities. Furthermore, the intensity distribution of the laser radiation inside the material for the different focus radii and focusing depths, and their dependence on the lateral and axial sizes of the voids was simulated and compared with the experimental results.

In recent years, the selective laser structuring from the transparent substrate side plays an increased role in thin film processing. The rear side ablation is a highly effective ablation method for thin film structuring and revels a high structuring quality. Therefore, the rear side ablation of nickel–chromium-alloy thin films on glass substrate was investigated using femtosecond laser irradiation. Single and multiple pulses ablation thresholds as well as the incubation coefficient were determined. By irradiation from the transparent substrate side at low fluences a cracking or a partly delamination of the film could be observed. By increasing the fluence the most part of the film was ablated, however, a very thin film remained at the interface of the glass substrate. This thin remaining layer could be completely ablated by two pulses. A further increase of the pulse number had no influence on the ablation morphology. The ablated film was still intact and an entire disc or fragments could be collected near the ablation area. The fragments showed no morphology change and were still in solid state.

This paper presents results obtained in high-pulse repetition frequency ultrashort pulse laser microprocessing of copper. In the study, a variety of ultrashort pulse laser systems supplying high average laser power were applied in order to investigate the influence of the laser parameters on copper ablation. For this, laser pulses of different wavelengths (515 nm, 1030 nm) and pulse durations, ranging between 200 fs and 10 ps, were irradiated to the sample surface by raster scanning of the laser beam. The dependencies of average laser power, pulse energy, and the pulse repetition rate on the ablation rate, the ablation efficiency, and the productivity were studied. A maximum average laser power of 31.7 W was applied in this work. The pulse repetition rate was varied in the rage between 0.2 and 19.3 MHz. Finally, the machining qualities obtained were evaluated by means of surface roughness measurements and scanning electron microscope micrograph analysis.

Selective realignment of the preferred magnetization direction in a laser micro structured GMR spin-valve layer system (Ni81Fe19/Co90Fe10/Cu/Co90Fe10/IrMn/Ni81Fe19) with a total film thickness of 23 nm was studied. For this, patterns of isolated microstructures (500 pin x 200 pin) were fabricated by laser ablation. These micropatterns were annealed using laser irradiation at a temperature above the IrMn Neel temperature. During laser annealing, the sample was subjected to an external magnetic field in order to selectively realign the magnetic direction of the reference layer. Two different laser assisted annealing techniques were investigated applying either continuous or pulsed laser systems. After laser annealing, the magnetic properties of the micropatterns were investigated using a magnetic microsensor and magneto optical Kerr effect set up. (C) 2014 Elsevier B.V. All rights reserved.

This paper presents results obtained in high-PRF (pulse repetition frequency) ultrashort pulse laser micro processing of copper. In the study, a variety of ultrashort pulse laser systems supplying high average laser power were applied in order to investigate the influence of the laser parameters on copper ablation. For this, laser pulses of different wavelengths (VIS, NIR) and pulse durations, ranging between 200 fs and 10 ps, were irradiated to the sample surface by raster scanning of the laser beam. The dependencies of average laser power, pulse energy, and the pulse repetition rate on the ablation rate, the ablation efficiency, and the productivity were studied. A maximum average laser power of 31.7 W was applied in this work. The pulse repetition rate was varied in the rage between 0.2 MHz and 19.3 MHz. Finally, the machining qualities obtained were evaluated by means of surface roughness measurements and SEM micrograph analysis.

The paper presents results obtained in a comparative study of laser irradiation of tungsten powder surfaces using a continuous wave fiber laser and a high repetition rate femtosecond laser. Depending on the energy input per unit length different melt structures have been produced. In general, if the same average laser power level was applied the structures show the same appearance independent from the laser source. But there was both a little higher degree of initial fusing and cross-linking along the processed path when the powder surface was irradiated with ultrashort pulses. Further, with increasing laser intensity a change in structure formation as well as a broadening of the laser processed path has been occurred, although the energy input per unit length remains constant. However, accumulation of slab-like structures, which was previously observed in high-intense ultrashort pulse laser irradiation, has been become more pronounced in cw laser irradiation above a certain number of consecutive scans. Moreover, characteristic effects, such as formation of ripples and nanomelt structures appearing in ultrashort pulse laser processing have been not detected in cw laser irradiation.

Laser irradiation of dispensed tungsten powder layers with grain sizes smaller than 1 mu m was investigated using high-repetition femtosecond laser systems. Laser processing was performed line by line with repetition rates up to 1 MHz and varying parameters such as laser power, processing speed, number of scans and pressure. In addition to the expected material ablation and melting, novel phenomena such as crystallisation, emergence of ripple structures, extensive agglomeration and the formation of nano-wires will be discussed qualitatively with the help of SEM photographs. Dependence on light pressure, pulse overlap and irradiated energy per unit length will be demonstrated. High-resolution microstructures will be discussed as a first application of innovative laser microsintering technology using high-repetition femtosecond laser pulses. DOI: 10.2961/jlmn.2012.01.0007

Laser micro processing using a high power single-mode continuous wave fibre laser in combination with a fast galvanometer scanner as well as an ultra fast polygon scan systems was investigated. As a key technology in high rate laser ablation a maximum laser power up to 3 kW and scan speeds up to 18,000 m/min were applied. With the ultra fast laser beam deflection and a small laser focal spot diameter of 21 mu m laser dwell times less than 100 nanoseconds were achieved. As a result laser intensities comparable to the q-switched lasers in the range of 10(8) W/cm(2) were irradiated on stainless steel, copper, and tungsten. The paper discusses the influence of the significant laser processing parameters, such as laser power, scan speed and scan number, on the ablation rate and the machining qualities. Furthermore initial ablation structures and micro-slits will be presented. DOI: 10.2961/jlmn.2012.01.0023

Laser microsintering of tungsten powder is investigated as a function of laser output power, pulse interval and vacuum level. The intensities are calculated for the evaporation thresholds of tungsten powder particles of various sizes. In addition, the powder layer generation and the resulting layer thicknesses are calculated. The powder abrasion occurring during the process was taken into consideration. Polished sections and REM images were prepared in order to analyse the experimental outcomes. The dependence of sinter density on the parameters is discussed.

Innovative rapid micro processing technologies were inv stigated by implementation of a high repetitio n rate femto second fibre laser and novel scanning sy stems. Previous experiments in femto second laser machining with high repetition rates indicated new mechanisms in laser matter interaction with the repetition rate as one of the mainly influencing pa rameter. Depending on temporal distances between th e laser pulses considerable changes of the ablation b ehaviour were detected, mainly caused by heat accumulation or particle shielding. Utilising high repetition rate laser technologies in 3d micro stru cturing, high ablation rates and short processing times were reported. A further reduction of processing times or laser irradiation with the maximal available laser power is limited by insufficient scan speed of commercial available galvanometer scanning systems. In this work high repetition rate laser micro processing of stainless steel was studied utilising both, a self-built resonant scanner and a fast galvanometer scanner system. Different laser proces sing regimes were investigated to demonstrate the possibilities and limits of the new technologies. T he important laser processing parameters were varie d nd parameter dependencies discussed by means of the wi dth and the depth of ablated gaps as soon as ablati on depths and processing qualities of laser generated thr e dimensional micro structures.

Previously, in high repetition rate femto second laser processing novel laser matter interacting effects were reported, such as heat accumulation and particle shielding. In this study, high repetition rate laser processing was investigated to discuss and understand the impact of laser repetition rate and accompanied accumulative laser material interacting effects. Therefore, a high repetition rate femto second fibre laser setup joint together with galvo scanner technology was applied in laser micro machining of metals (copper, stainless steel, aluminium). High repetition rate laser processing of aluminium and stainless steel lead to considerably lowered ablation thresholds accompanied with higher ablation rates. Laser ablation behaviour of copper was almost independent of the repetition rate with neither considerable lower ablation thresholds nor higher ablation rates. For explanation, heat accumulation caused by higher repetition rates were assumed as mainly ablation behaviour influencing effect, but thermal material properties have to be considered.Furthermore laser machining examples demonstrate the possibilities and limits of high repetition rate laser processing in 3d micro structuring. Thus, by using innovative scanning systems and machining strategies very short processing times were achieved, which lead to high machining throughputs and attract interest of the innovative laser technology in Rapid Micro Tooling. For discussion, high repetition rate processing results are evaluated by means of comparative machining examples obtained with 1 kHz femto second laser system.

Intended for novel machining strategies in high power laser machining, a continuous wave single mode fibre laser (YLR-3000-SM, IPG) with a laser power up to 3 kW and a brilliant beam quality M-2 < 1.2 has been applied in the presented work. Laser beam focusing was realised by industrial standard machining setups: large area scanning systems (RLSK; HighYAG), high speed scanning systems (Superscan; Raylase) and a stationary welding optic (YW50; Precitec). Laser welding of stainless steel has been investigated to compare significant interacting mechanism for different machining technologies. Butt joint welding and bead-on-plate welding have been applied under a range of various processing parameters, such as objective focal length, processing velocity, and laser output power. Ablation cutting on stainless steel and high-purity Al2O3 ceramics has been investigated subjected to various machining conditions. For discussion, the dependence of important laser processing parameters onto ablation depth has been indicated, and texture analyses show the material behaviour before and after the machining process. DOI:10.2961/jlmn.2010.02.0006