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Mechanisms responsible for the limitation of the aspect ratio obtained by deep drilling of hard metals are investigated in the present work. Cemented carbide targets have been irradiated with laser pulses of 100 fs duration and 100 μJ maximum energy delivered by a Ti:sapphire laser system. The experiments are carried out in different gas environments (vacuum, air, helium up to atmospheric pressure) with incident laser fluences ranging from 1 to 20 Jcm-2. During deep drilling, the laser-induced ablation plume is characterized by means of in-situ plasma diagnostics. Fast imaging is used to observe the expansion behavior of the plasma plume whereas time- and space-resolved emission spectroscopy is employed to analyze the plasma composition. After irradiation, the laser-produced craters were examined by optical microscopy. A correlation between the ablation plume characteristics and the morphological changes of the mciro-holes is established. The results indicate that nanoclusters, that present a significant part of the ablated material, are responsbile for the alteration of the crater shape in the high laser fluence regime.

Polycrystalline SiGe is attracting more and more attention in micro and optoelectronics devices both at industrial and university level. Research on both devices and material growth techniques continues at a very rapid pace in the scientific world. Low cost production techniques, capable to produce such alloys with uniform and controlled grain size, becomes of particular attention. Excimer laser crystallization has proved to be a valuable how thermal budget technique for amorphous silicon crystallization. Its main advantages are the high process quality and reproducibility joint to the possibility of tailoring the grain sizes both in small selected regions and in large areas. This technique is here applied for producing poly-SiGe alloys from amorphous SiGe films deposited on glass.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Investigations on the occurrence of structure and hardness changes (for two sorts of steel and for a hard metal substrate) in the immediate vicinity of laser induced craters are presented in this work. Experiments with femtosecond pulses were performed in air with a Ti:sapphire laser (800 nm, 100 fs) at mean fluences of 2, 5 and 10 J/cm2. Series of microcraters were induced with 100 to 5,000 laser pulses per hole. Experiments with similar fluences, but 10 to 40 pules per hole, were performed on the same materials using a Nd:YAG delivering 100 ns pulese. After laser irradiation, cuts were made through the processed samples and the changes occurred in the crystalline structure of the target materials were evidenced by metallographical analysis of the resulting cross-sections. Hardness measurements were performed in points situated in the immediate vicinity of the laser-induced pores. Affected zones in the material surrounding laser induced pores were always found in the ns-regime, however with different properties for various laser parameters. In the fs-regime, zones of modified materials were also found and in such zones a significant hardness increasing was evidenced; the limit of the low fluences regime, where no structure changes occurred, was found to be slightly above 2 J/cm2.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The controlled laser patterning of solid surfaces improves their wear properties: laser generated microcraters of defined dimensions and morphology can act as lubricant reservoirs and as traps for wear particles. For generating such microstructures different techniques are possible; however laser ablation has the advantage of a great versatility, since it can be adapted to produce a wide range of structures crater arrangements. We have generated microstructures with ps- and ns- pulses on TiN coated steel, uncoated steel and on uncoated steel with was subsequently coated with TiCN. Laser patterning of metals with pulses in the 100ns range is very effective however the process is governed by local melting and vaporization. The melt ejection yields the formation of resolidified droplets and rims on the target surface. This undesired artifacts can be removed by gentle polishing. Furthermore, a recast layer of increased hardness and brittleness of about 1µm thickness which homogeneously covers the crater walls is observed. Tribological tests were performed using the ball-on-disk method. The lifetime of the structured samples, defined as the sliding distance after which the friction coefficient showed an abrupt increase, was found to be significantly enhanced for all structured surfaces. The enhancement ranged from a 30% lifetime increase when TiN coatings were directly structured to an increase of over 10 times for structured hard metal which was subsequently coated with TiCN. To evaluate the possibility of circumventing some of the drawbacks of laser ablation in the ns regime, mainly the melt rims on the surface and the recast layer film on the crater walls of the single microholes the quality of microstructures produced in various metals with pulses of femtosecond duration was studied. To that end the evolution of the ablated depth over a large number of incident femtosecond laser pulses and the occurrence of structure and hardness changes in the immediate vicinity of the laser induced craters was analyzed for two sorts of steel and for hard metal. The analysis evidenced changes in the crystalline structure of the target materials in the fluence regime above 2J/cm2 but only minor alterations up to this fluence. Hardness measurements were performed on the cross-section surfaces in points situated in the immediate vicinity of the laser induced pores. Affected zones in the material surrounding few pores induced in the fs- regime were found and in such zones a significant hardness increasing was evidenced.

The controlled laser microstructuring of solid surfaces improves their wear properties: microholes induced on a friction surface can act like lubricant reservoirs and as traps for debris particles. In generating such microstructures, the laser has the advantage of its great versatility, since it can be used in various environments and it can be adapted to a wide range of desired structures. In this work metallic surfaces where precisely and reproducibly patterned on a micrometer scale by an industrial, Q-switch-operated Nd:YAG laser. The duration of the pulses was 100 ns FWHM. For laser ablation in this pulse length range local melting and vaporing govern the mechanisms of materials expulsion and the melt ejection occurs through the vapor pressure gradient, yielding the formation of resolidified droplets and rims on the target surface.