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The performance of CoFeB/MgO tunnel junctions is strongly dependent on an annealing step at the end of the fabrication process to first, set a reference magnetization through the exchange bias effect and second, to crystallize the MgO/CoFe layers while boron diffuses out, in order to maximize the magnetoresistance ratio. In this regard, a laser-induced annealing process presents several advantages against traditional oven annealing techniques, providing a scalable approach with no limitations regarding the defined reference magnetization that can be aligned in different directions on a wafer. This paper concentrates on the mechanisms and dependences of laser annealing on the magnetic properties in comparison to the standard vacuum oven annealing, providing a first insight for the applicability of laser annealing for CoFeB-/MgO-based magnetic tunnel junctions with all concomitant needs.

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.

The determination of the local field direction enables, for instance, migratory birds to find their annual routes from one continent to another, or magnetotactic bacteria to move towards soil rich in nutrients. In analogy, for microelectromechanical systems (MEMS), the ability of detecting the local direction of a magnetic field as a 2D or 3D vector can allow, in principle, a reliable autonomous navigation through environments with a complex or unknown topology. These applications demand, however, a very low power consumption, miniaturizability and fast response times in the milliseconds range. In the following, we present novel 2D sensors based on exchange-biased IrMn / CoFe / Cu / CoFe – NiFe spin valves fulfilling all these requirements. In addition, we test different sensor arrangements. The spatial sensitivity of the constituent single GMR meanders is defined by means of microscopic laser heating and subsequent in-field cooling. By this, a relative pairwise geometric alignment of 90° or 180°, respectively, is achieved for the individual antiferromagnetic pinning layers, providing a maximum signal response for each sensor layout. On the basis of fabricated prototypes with a size of < 0.5 mm2, we demonstrate that these sensors can readily be employed to detect small magnetic fields as a 2D vector with a high temporal resolution of 100 μs.

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.

The performance of exchanged biased tunnel junctions strongly relies on the annealing process finalizing the fabrication process, which is applied to set a pinned reference magnetization, as well as to enhance the magnetoresistance ratio through the crystallization of the CoFeB layers. With the increasing demand in terms of integration and scalability of tunnel magnetoresistive elements, a laser-induced annealing process presents several advantages against traditional oven annealing technique. It provides the possibility to locally set an individual reference magnetization at the micrometer scale to enable e.g. a Wheatstone bridge or multidimensional sensor fabrication on a wafer level. This study presents the influence of laser-induced localized annealing on the magnetic properties of an exchanged biased CoFeB/IrMn system. The diffusion processes occurring at the interface of CoFeB/IrMn are analyzed in detail utilizing X-ray photoemission spectroscopy depth profiling technique and the results are compared to those obtained by standard vacuum oven annealing and correlated to the magnetic properties investigated by magneto-optical Kerr effect magnetometry.

Laser micro processing using a high power single-mode continuous wave fibre laser in combina-tion 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/minwere applied. With the ultra fast laser beam deflection and laser a smallfocal spot diameter of 21 µm laser dwell times less than 100 nanoseconds were achieved. As a result laser intensities comparable to the q-switched lasers in the range of

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 < 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.

Laser micro sintering (LMS) was developed by the research group at University of Applied Sciences Mittweida and the associated Laserinstitut Mittelsachsen e.V. as the result of research started in 2001 with a project on the possibility of generating parts by selective laser sintering (SLS) with improved resolution. For the successful generation of solid bodies from various metal powders the technology uses essentially sub-micrometer powders, a cylindrical coating blade and a q-switched solid state laser. The resolution and the surface roughness are by more than one order of magnitude better than those achieved by previous selective laser sinter technologies. Presently the technology shows advancements in selective laser sintering of highly resolved specimens of densely sintered Al2O3 and SiC ceramics too. This paper reports the process mechanism of LMS and its principal differences compared to other SLS methods. A variety of laser micro sintered parts from different metals and the newest results in laser ...

Miniaturization is one of the main imperatives in high-tech development and therefore a persistent challenge for mechanical engineering. Recently a freeform technique – Laser Micro Sintering – has been developed by which micro parts with an overall resolution of 30 μm can be produced from powder materials. The technique is a generative freeform fabrication method based on selective laser sintering; it can produce hollows and undercuts and does not afford shape-specific tools. Functional micro bodies can be generated from metals and ceramics.

We have designed and fabricated 2D GMR spin valve sensors on the basis of IrMn/CoFe/Cu/CoFe/NiFe nanolayers in monolithic integration for high sensitivity applications. For a maximum signal-to-noise ratio, we realize a focused double full bridge layout featuring an antiparallel exchange bias pinning for neighbouring meanders and an orthogonal pinning for different bridges. This precise alignment is achieved with microscopic precision by laser heating and subsequent in-field cooling. Striving for maximum signal sensitivity and minimum hysteresis, we study in detail the impact of single meander geometry on the total magnetic structure and electronic transport properties. The investigated geometrical parameters include stripe width, stripe length, cross bar material and total meander length. In addition, the influence of the relative alignment between reference magnetization (pinned layer) and shape anisotropy (free layer) is studied. The experimentally obtained data are moreover compared to the predictions of tailored micromagnetic simulations. Using a set of optimum parameters, we demonstrate that our sensor may readily be employed to measure small magnetic fields, such as the ambient (geomagnetic) field, in terms of a 2D vector with high spatial (~200 μm) and temporal (~1 ms) resolution.

Since the discovery of selective laser sintering/melting, numerous modifications have been made to upgrade or customize this technology for industrial purposes. Laser micro sintering (LMS) is one of those modifications: Powders with particles in the range of a few micrometers are used to obtain products with highly resolved structures. Pulses of a q-switched laser had been considered necessary in order to generate sinter layers from the micrometer scaled metal powders. LMS has been applied with powders from metals as well as from ceramic and cermet feedstock’s to generate micro parts. Recent technological progress and the application of high brilliant continuous laser radiation have now allowed an efficient laser sintering/melting of micrometer scaled metal powders. Thereby it is remarkable that thin sinter layers are generated using high continuous laser power. The principles of the process, the state of the art in LMS concerning its advantages and limitations and furthermore the latest results of the recent development of this technology will be presented. Laser Micro Sintering / Laser Micro Melting (LMM) offer a vision for a new dimension of additive fabrication of miniature and precise parts also with application potential in all engineering fields.

Micro Cladding stellt eine Modifikation des klassischen Laserpulverauftragschweisens dar, um grosflachig und flexibel Mikrostrukturen auf nahezu beliebigen Oberflachen aufbringen zu konnen [1][2]. Die Besonderheit des am Laserinstitut Hochschule Mittweida entwickelten Verfahrens sind dabei der Einsatz eines kurzgepulsten Faserlasers mit einer schnellen Strahlablenkung mittels Galvanometer-Scanner sowie die Ausbildung von Mikrostrukturen zur Speicherung des Pulvers [3][4][5]. Hierdurch kann die Laserstrahlenergie auch im Mikrobereich lokal begrenzt eingebracht und die Volumenbaurate gesteigert werden. Die Auflosung des Verfahrens liegt aktuell bei ca. 40 μm. Fur mehr industrielle Relevanz wurden die Volumenbauraten durch Anwendung von Hochleistungslasern und schnellen Scannern auf bis zu 3.900 mm³/h deutlich erhoht. Die Ergebnisse der Untersuchungen werden aufgezeigt und die Verfahrensgrenzen diskutiert.

Additive manufacturing (AM) offers a quick and efficient method for prototyping and small batch production with a short delivery time or even individual parts. Components of high geometrical complexity can be directly shaped from metals, metal-alloys, metal-matrix composites and from ceramic materials. By a suitable choice of the process parameters AM produced components can meet the demanding requirements of the aerospace, automotive and biomedical industries. Laser micro sintering (LMS) as a further development of selective laser sintering uses fine grained powders below 10 µm to produce high accuracy 3D structures (

We report on selective realignment of the magnetization direction of the exchange biased ferromagnetic layer in two different spintronic layer stacks using laser radiation. The exchange bias effect occurs in an antiferromagnetic/ferromagnetic bilayer system when cooled in an external magnetic field below the Neel temperature and results in a shift of the ferromagnetic hysteresis loop with increased coercivity. The effect is utilized to pin the magnetization direction of the reference ferromagnetic layer in spin valve systems. We investigated the realignment of the pinned magnetization direction in a spin valve system with in plane exchange bias and in a Co/Pt multilayer with perpendicular exchange bias. The layer stacks were heated above the Neel temperature in a defined lateral area by using rapidly deflected laser radiation. Two different laser assisted annealing techniques were investigated applying either continuous or pulsed laser radiation. During laser annealing, the sample was subjected to an external magnetic field in order to selectively realign the magnetization direction of the pinned ferromagnetic layer. Magnetic structuring was performed by heating narrow single tracks as well as irradiating single pulses. By using a magneto optical sensor in combination with a polarization microscope, the magnetic structures have been visualized. After laser annealing of larger-scaled areas, the exchange bias field strength and the coercive field strength were analyzed using a magneto optical Kerr effect set up (MOKE). The impact of the processing parameters laser peak intensity, laser pulse duration, scan speed (continuous wave) and magnetic field strength on the resulting reversed exchange bias field was evaluated.

We report on a fast machining process for cutting silicon wafers using laser radiation without melting or ablating and without additional pretreatment. For the laser induced cutting of silicon materials a defocused Gaussian laser beam has been guided over the wafer surface. In the course of this, the laser radiation caused a thermal induced area of tension without affecting the material in any other way. With the beginning of the tension cracking process in the laser induced area of tension emerged a crack, which could be guided by the laser radiation along any direction over the wafer surface. The achieved cutting speed was greater than 1 m/s. We present results for different material modifications and wafer thicknesses. The qualitative assessment is based on SEM images of the cutting edges. With this method it is possible to cut mono- and polycrystalline silicon wafers in a very fast and clean way, without having any waste products. Because the generated cracking edge is also very planar and has only a small roughness, with laser induced tension cracking high quality processing results are easily accessible.

Selective realignment of the preferred magnetization direction in a laser micro structured GMR spin-valve layer system (Ni 81 Fe 19 /Co 90 Fe 10 /Cu/Co 90 Fe 10 /IrMn/Ni 81 Fe 19 ) with a total film thickness of 23 nm was studied. For this, patterns of isolated microstructures (500 μm × 200 μm) 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.

The process of contactless laser bending using the laser induced thermal stresses that up to this moment is performed with steels and other metal alloys is firstly applied to silicon microstructural elements. One-side-fastened Si beams prepared by anisotropic wet etching were locally heated by a Nd:YAG laser. The beams were bent without additional tools towards the incident laser beam. Bending angles up to 90° are realizable. The degree of bending is strongly dependent on the used laser parameters, the position of heating and the number and distance of the laser scans.

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.

In laser ablation cutting, irradiation of high-intense laser beams causes ejection of molten and evaporated material out of the cutting zone as a result of high pressure gradients, induced by expanding plasma plumes. This paper investigates highspeed laser ablation cutting of industrial grade metal sheets using high-brilliant continuous wave fiber lasers with output powers up to 5 kW. The laser beam was deflected with scan speeds up to 2700 m/min utilizing both a fast galvanometer scan system and a polygon scan system. By sharp laser beam focusing using different objectives with focal lengths ranging between 160 mm and 500 mm, small laser spot diameters between 16.5 μm and 60 μm were obtained, respectively. As a result high peak intensities between 3*108 W/cm² and 2.5*109 W/cm² were irradiated on the sample surface, and cutting kerfs with a maximum depth of 1.4 mm have been produced. In this study the impact of the processing parameters laser power, laser spot diameter, cutting speed, and number of scans on both the achievable cutting depth and the cutting edge quality was investigated. The ablation depths, the heights of the cutting burr, as well as the removed material volumes were evaluated by means of optical microscope images and cross section photographs. Finally highspeed laser ablation cutting was studied using an intensified ultra highspeed camera in order to get useful insights into the cutting process.

Since a few years, high brilliance laser sources find their way into laser material processing. Laser micro processing by applying high brilliance laser radiation up to 3 kW of continuous wave laser power in combination with ultrafast beam deflection systems has been successfully demonstrated in 2008 for the first time. In the fields of laser welding, high brilliant laser radiation was mainly used for micro welding, but up to now the macro range is still insufficiently investigated. Hence, this study reports on detailed investigations of high speed laser welding of different steel grades, performed with a high power single mode fiber laser source. The laser beam was deflected relative to the sample by using both a fast galvanometer scanner system with f-theta focusing objective and a linear axis in combination with a welding optic, respectively. In the study, the mainly process influencing parameters such as laser power, welding speed, thickness of the metal sheets, angle of incidence and laser beam spot size were varied in a wide range. The weld seam quality was evaluated by structural analyses, static tensile tests and EDX measurements. Finally, the laser welding process has been optimized for different weld seam geometries, for example bead-on-plate welds and butt welds.

In this paper processing of transparent materials by laser radiation from various sources with short (nanoseconds) and ultrashort (femtoseconds) pulse lengths at different wavelengths is discussed. The investigations were carried out with a short pulse Nd:YVO 4 laser (1064 nm, 532 nm) and a high repetition rate femtosecond fiber laser (1030 nm). In our experiments the laser beam was guided across the probe either through the motion of a coordinate table or through a laser scanner with an f-theta-objective. In our study we investigated in detail the influence of important process parameters like wavelength, pulse width, and irradiation regime upon micro defect generation inside bulk glass (BK glass, fused silica) and polymers (polymethylmethacrylate, polycarbonate, cyclo-olefin-copolymers). By applying an irradiation regime with optimal process parameters these locally confined material defects can be aligned as to yield cut surfaces for the excision of 3d parts that consist of transparent material with bulk properties. Especially for the production of irregularly shaped 3d parts a CAD-CAM software tool was developed that automatically converts geometry data into a processing program.

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 high-quality machining results with a minimal thermal load and a roughness Ra 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 three-dimensional micro structured machining examples.

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.

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.

The paper presents an overview about high repetition rate femto second laser machining and its applications. Novel phenomena in laser matter interaction with the repetition rate as one of the mainly influencing parameter are discussed. Depending on temporal distances between consecutive femto second laser pulses, either heat accumulation or particle shielding effects were detected. Heat accumulation enhanced the ablation behavior and higher ablation rates were found. On other hand energy losses due to particle shielding caused lowered ablation rates. Furthermore laser induced periodical surface structures, such as ripple formations and conical micro structures, were observed due to the high average laser energy input and accumulative effects. Formation und shape properties of these structures depend on laser processing parameter.Joining high repetition rate laser technology together with high speed beam deflection systems, significantly higher ablation rates and short processing times were achieved. Exemplarily demonstrated in 3D micro structuring, processing times were reduced more than 40 times compared to fs laser processing using repetition rates of some kHz. In consequence, prospectively high machining throughputs were reached, which attract increasing interest of the novel technology in industrial applications.The paper presents an overview about high repetition rate femto second laser machining and its applications. Novel phenomena in laser matter interaction with the repetition rate as one of the mainly influencing parameter are discussed. Depending on temporal distances between consecutive femto second laser pulses, either heat accumulation or particle shielding effects were detected. Heat accumulation enhanced the ablation behavior and higher ablation rates were found. On other hand energy losses due to particle shielding caused lowered ablation rates. Furthermore laser induced periodical surface structures, such as ripple formations and conical micro structures, were observed due to the high average laser energy input and accumulative effects. Formation und shape properties of these structures depend on laser processing parameter.Joining high repetition rate laser technology together with high speed beam deflection systems, significantly higher ablation rates and short processing times were achieved. Exemp...

Laser micro sintering, a modification of selective laser sintering for the freeform fabrication of micro-parts, has been developed continuously since its first application. The main feature of the original regime was the application of non-overlapping q-switched pulses which was required because of the poor density of the powder layers and the concomitant need for a compacting effect during the laser sinter process. Next to some unanticipated positive side effects of this regime, poor compactness of the products had to be taken into account frequently as a detrimental consequence. Recently an upgraded coating routine has been developed that contains a compaction-step of the powder coating prior to the sintering of each layer. After appropriate adaption of the laser regime micro-parts with considerably higher densities can be achieved now. Process observations and the properties of the sintered solids give evidence that a different sinter mechanism takes place with its own negative and positive side effects. The conclusion can be made that, with sufficiently compacted powder layers and sufficient control of the coating, even laser micro sintering with continuous radiation might be feasible. Direct generation of highly miniaturized machines with encased freely movable entities by the upgraded technique has been proved. The new technology is named HD-LMS (“High Density-Laser Micro Sintering”).Laser micro sintering, a modification of selective laser sintering for the freeform fabrication of micro-parts, has been developed continuously since its first application. The main feature of the original regime was the application of non-overlapping q-switched pulses which was required because of the poor density of the powder layers and the concomitant need for a compacting effect during the laser sinter process. Next to some unanticipated positive side effects of this regime, poor compactness of the products had to be taken into account frequently as a detrimental consequence. Recently an upgraded coating routine has been developed that contains a compaction-step of the powder coating prior to the sintering of each layer. After appropriate adaption of the laser regime micro-parts with considerably higher densities can be achieved now. Process observations and the properties of the sintered solids give evidence that a different sinter mechanism takes place with its own negative and positive side effect...

Many materials have already been investigated for laser micro sintering. Nearly all technical metals can be processed with this rapid prototyping technology. A new field of investigation is the sintering of ceramics. For industrial and also for medical, especially dental, application silicon dioxide is a multiply applicable material. One of its interesting features is that the properties of the resulting material can be varied between ceramic on the one and vitreous on the other side, depending on the extent of crystalline or amorphous character of the nano-scale structure. A special problem with laser micro sintering of ceramics is the poor absorption of Nd:YAG laser radiation by most of the materials. Besides that, laser micro sintering of ceramics, in contrary to the process with metals, is not merely a series of aggregational transitions. A solution for the micro part generation of SiO2 is reported. Typical laser sintering results from this material are presented. Material specific behaviors during laser micro sintering are discussed.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper first results on 3d laser cutting of glasses as a technology for rapid tooling, obtained at the laser institute of the University of Applied Sciences Mitt-weida, are presented. The investigations were carried out with a short pulse Nd:YVO4 slab laser from Edge-wave (Aachen) and a high repetition rate femtosecond laser of Clark-MXR Inc. Michigan. In the experiments the laser beam was focussed onto the sample with both a stationary aspheric lens and a laser scanner with an f-theta-objective combined with a high precision xyz-axis stage.The technique utilizes nonlinear absorption effects to induce local heating, followed by stress generation and finally micro defect formation inside the transparent bulk material. Several side effects have to be considered in machining of transparent materials, for example, nonlinear processes like self focussing and the focal shift.In the beginning for various glasses the dependence of the micro defect formation on the process parameters were investigated in detail - possibilities and limits are discussed. The development of strategies of applicable arrangements of micro defects to produce fracture lines, planes and shells enclosing the required component are object of the investigations in order to produce 3d parts. These components created with the presented technology are consisting of bulk material - the key benefit in comparison to laser sintered parts.In this paper first results on 3d laser cutting of glasses as a technology for rapid tooling, obtained at the laser institute of the University of Applied Sciences Mitt-weida, are presented. The investigations were carried out with a short pulse Nd:YVO4 slab laser from Edge-wave (Aachen) and a high repetition rate femtosecond laser of Clark-MXR Inc. Michigan. In the experiments the laser beam was focussed onto the sample with both a stationary aspheric lens and a laser scanner with an f-theta-objective combined with a high precision xyz-axis stage.The technique utilizes nonlinear absorption effects to induce local heating, followed by stress generation and finally micro defect formation inside the transparent bulk material. Several side effects have to be considered in machining of transparent materials, for example, nonlinear processes like self focussing and the focal shift.In the beginning for various glasses the dependence of the micro defect formation on the process parameters were investigated in de...

The selective laser micro sintering (SLS), which was developed by the Laserinstitut Mittelsachsen e.V. (Ebert 1999) is used for generation of micro parts. Tungsten and tungsten alloys (especially tungstenaluminium) were employed as the first usable metal powders for laser micro sintering (Regenfuss 2003), (Exner 2003). Meanwhile many new materials were investigated (Regenfuss 2005).

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.

In this paper we are going to present FEM calculations applied for laser bending of silicon microstructures and compare them with our experimental results. According to the mechanisms in plastic deformation of metals with laser radiation we performed calculations to find out, if there are similar mechanisms in forming of silicon. To model the laser heating up mechanism we have to take into account several physical effects like heat radiation or reflection of silicon for the used laser radiation. To transform the laser bending process into a FE model the boundary conditions include compromises and simplifications of the geometry and the energy input. In our calculations we modelled the laser beam as a moving heat source in order to get information about the temperature distribution, the temperature gradient and the heat flow in dependence on the position on the sample and the time. The calculated essentially higher temperatures at the edges of the structure compared to the middle of the structure, exceeding the melting point there, are in very good agreement to the melting areas observed at the edges in the experi-ments. After a number of consecutive scans we reach a balanced temperature field moving with the laser beam across the surface. The calculations revealed that there is a steep temperature gradient in the depth of the structure indicating a similar temperature gradient mechanism observed in forming of metals with laser radiation. Additionally we carried out temperature field calculations to determine the influence of the process parameters like the laser power, the velocity of the heat source, the material thickness or the position of laser treatment on the temperature field generated in the material. The results of the calculations are in very good agreement with our experiments. Next time stress field calculations are intended. At the moment there are not enough data on the plastic behaviour of silicon available to the authors in order to get reliable results.

PurposeExamples are given for the technical applicability of a novel development of selective laser sintering called “laser micro sintering”.Design/methodology/approachTogether with a specific method to produce powder layers, the controlled application of pulsed radiation for the processing of sub‐μm grained metal powders was exploited to produce micro‐tools with a heretofore unattained structural resolution.FindingsHigh resolution micro bodies are displayed. Instruments could be generated which proved to fulfil their designation as grip bits for micro manipulators. The micro‐bodies can be generated detachably from or firmly fixed to the construction substrate. The material of the generated bodies withstands the traction forces when used as an injection mold for polymer casts.Research limitations/implicationsDensities and structural resolutions can still be improved especially with a newly updated version of the equipment. Laser micro sintering of materials, other than metal (e.g. ceramics), has still to be developed. The introduction of the equipment and the technique into the market is on its way.Practical implicationsMicro‐tools can be generated with an overall structural resolution of 30 μm and with all the advantages of a freedom technique.Originality/valueThe paper informs the technical community on a new novel modification of the freeform technique selective laser sintering, demonstrating the solution of some problems that have hampered the progress of metal laser into resolution ranges below 100 μm. It also supplies evidence for the technical applicability.

As mechanical engineering industry encounters a growing demand of µm-sized or µm-structured components for an increasing range of applications, miniaturization is presently ranking among the most important goals in product and tool development.Compared to still higher resolving techniques, selective laser sintering (SLS) still bears the advantages of relatively low production cost and short processing times even for series productions of micro parts. Furthermore, next to prismatic or tapered microstructures, undercuts and hollows can be realized.Until recently commercial SLS units were unable to generate micro parts smaller than 100 µm. A novel modification of SLS together with a new setup, developed by Laser Institut Mittelsachsen e.V, extends the resolution to less than 30 µm with a minimal roughness of 1.5µm. The technique has been upgraded and successfully applied to produce micro tools or micro-components for tools from powders of refractory as well as lower melting metals in steps of 1µm thick sintered layers.Based on this process and device, 3D-Micromac AG (Chemnitz, Germany) launches into the market a commercial system, which, on an industrial scale, performs selective laser sintering of solid and structured metal and in future also ceramic parts.As mechanical engineering industry encounters a growing demand of µm-sized or µm-structured components for an increasing range of applications, miniaturization is presently ranking among the most important goals in product and tool development.Compared to still higher resolving techniques, selective laser sintering (SLS) still bears the advantages of relatively low production cost and short processing times even for series productions of micro parts. Furthermore, next to prismatic or tapered microstructures, undercuts and hollows can be realized.Until recently commercial SLS units were unable to generate micro parts smaller than 100 µm. A novel modification of SLS together with a new setup, developed by Laser Institut Mittelsachsen e.V, extends the resolution to less than 30 µm with a minimal roughness of 1.5µm. The technique has been upgraded and successfully applied to produce micro tools or micro-components for tools from powders of refractory as well as lower melting metals in steps of 1µm thick sinte...

The results of our investigations on femtosecond-laser micromachining of Pyrex and quartz glass are presented. The investigations were done using a micromachining station from the 3D-Micromac AG Chemnitz into which a Clark MXR fs-laser CPA 2010 (775 nm mean wavelength, 130 fs pulse duration) is implemented. It is shown how the parameters of the microstructures produced in the materials depend on the processing parameters. By drilling the pyrex glass in vacuum, an increase of the average removal rate per laser pulse by the factor of 2.3 was achieved compared to the drilling under normal conditions but otherwise unchanged parameters. The formation of cracks in the vicinity of the holes or on the walls due to the laser machining was not observed, neither with Pyrex nor with quartz glass. There may occur, however, chunkings on the side of the laser beam exit of through holes.The results of our investigations on femtosecond-laser micromachining of Pyrex and quartz glass are presented. The investigations were done using a micromachining station from the 3D-Micromac AG Chemnitz into which a Clark MXR fs-laser CPA 2010 (775 nm mean wavelength, 130 fs pulse duration) is implemented. It is shown how the parameters of the microstructures produced in the materials depend on the processing parameters. By drilling the pyrex glass in vacuum, an increase of the average removal rate per laser pulse by the factor of 2.3 was achieved compared to the drilling under normal conditions but otherwise unchanged parameters. The formation of cracks in the vicinity of the holes or on the walls due to the laser machining was not observed, neither with Pyrex nor with quartz glass. There may occur, however, chunkings on the side of the laser beam exit of through holes.

A novel device suited for the generation of sintered microparts of metal and ceramics, for reaction sintering and for CVD has been developed and successfully tested. With the production of a functional component it has evidenced professional performance. The set-up is vacuum tight; unstable substances can be processed under various shield gases and pressures; it is equipped with a device suited to rake thin layers of fine powders as well as slurries. Sub micrometer powder can be processed in steps of 1 μm thick sintered layers. In combination with a proprietary sintering regime, micro parts with a structural resolution of 10 have been achieved.

Microparts with a structural resolution of 12 have been generated by selective laser sintering. The technique includes sintering under conditions of vacuum or reduced shield gas pressures. In a novel set-up the material is processed by a Q-switched 1064nm Nd-YAG laser after a special raking procedure. The procedure allows the work pieces to be generated from powders of high melting metals like tungsten as well as lower melting metals like aluminium and copper. Contingent on the parameters, the generated bodies are either firmly attached to the substrate or can be dissevered by a non-destructive method.

We are going to present a new technology for laser machining of silicon developed at the Laser Institute of Mittweida by a suggestion and in cooperation with the Technical University of Chemnitz, Department of Electrical Engineering and Information Technology. It allows the laser induced bending of microstructural silicon elements prepared by anisotropic wet etching. Bending of the element toward the incident laser beam occurs as a result of the laser induced thermal stresses in the material. We investigated the influence of various process parameters on the bending angle. There is only a small range of laser power to generate bendings in silicon. We will show a variety of examples including multiple and also continuous bendings. There are several essential advantages compared to conventional bending technologies: Laser bending is a contactless process without using additional tools or external forces. Because of the local laser treatment the heat flux to neighbouring material can be minimized so that the technology is suitable for machining of already finished microsystems. This new technology opens up a new field of applications in microsystem technologies. It is possible to generate a clip-chip-mechanism to clip a chip in a holder. Other examples are the exact positioning of optical mirrors or other components, the production of electrostatic drives and sliding chips for micro optical benches.

We are going to present a new technology for laser bending of silicon microstructures based upon a suggestion of and carried out in cooperation with Prof. Dr. J. Fruhauf from the Technical University Chemnitz (see acknowledgement). We investigated the influence of various laser process parameters on the bending angle and its reproducibility. Bending of the silicon element as a result of the laser induced thermal stresses in the material occurs toward the incident laser beam. The bending angle depends on a lot of laser process and material parameters. In particular we found that the irra-diation regime is well suited to control the bending angle. First substantial FEM based calculations of laser induced temperature fields using a moving laser heat source show the temperature field propagation in the material and reveal some regions of complicated overheating. As a result of our experiments we show a variety of examples including mul-tiple and also continuous bendings. There are several essential advantages compared to conventional bending technologies with this new method: Laser bending is contactless without using additional tools or external forces. Because of the local laser treatment the heat flux to the neighbouring material is minimized. The laser beam can be applied through windows of glass that means to al-most hermetically sealed micro devices. So laser technology is suitable for machining of already finished microsystems. It opens up a wide field of applications in micro system technologies: clip-chip-mechanism or sliding chips for micro optical benches, the adjustment of optical mirrors or other components or the ability of continuous bending for electro-static drives and so on.

Presently, there is a growing demand from the industry for microprocessing of materials. For applications in microsystems technology and biotechnology it is particularly necessary to produce structures with dimensions down to the micrometer scale. This refers especially to materials that can not or not in a sufficiently quality be processed by conventional methods of silicon technologies. In order to fulfil the industrial demands we have investigated the structuring of anodic bondable PYREX glass and of polymers by means of laser microprocessing using the excimer laser mask projection technique (193 nm wavelength, 10 ns pulse duration, 8 mJ pulse energy, 500 Hz repetition rate). In our paper we will show the dependence of the obtained quality especially the roughness of the generated surfaces on the processing parameters. The possibilities of our technology including the creation of holes, channels and three dimensional microstructures will be presented too. Single structures e.g. bridges and grooves are attainable with widths of 10 micrometers and below. Some of the drilled holes (diameter about 50 µm) have been successfully filled inside with aluminium by a laser assisted CVD process.

Presently, there is a growing demand from the industry for microprocessing of materials. In particular, for applications in the field of microsystems technology it is necessary to produce structures with dimensions down to the micrometer scale in various materials. We have been investigating the structuring of silicon, anodic bondable PYREX glass, Al 2 O 3 -ceramic and PMMA by means of laser microprocessing using an excimer laser (248 nm or 193 nm wavelength, 30 ns pulse duration, 400 mJ pulse energy) and a TEA CO 2 laser (10,6 μm wavelength, 80 ns or 200 ns pulse duration, 6 J pulse energy). Both the mask projection technique and the focusing technique have been employed. We will show the dependence of the ablation thresholds and the ablation rates on the laser parameters and on the'physical properties of the materials, i.e. absorption coefficient, melting point and thermal conductivity. During and after the laser processing of different glasses we observed the formation of cracks in the laser irradiated region and partly in the glass wafer surrounding the drilled holes. Those crack formations should be due to the development of thermally induced mechanical stress in the glass. We calculated the TEA CO 2 laser ablation process using a half empirical rotation symmetrical model.

We are presenting a very successful new method of a laser welding technology developed in the Laser Institute of Mittel-sachsen. It allows us to join parts of alumina without any changes of their properties base don an additive free procedure. Furthermore it enables us to carry out the procedure without furnaces and in natural atmosphere within only a few minutes. In order to avoid thermally included stresses two laser beams are used. We will describe this procedure of laser welding of ceramics including the manner of preheating: their limits and advantages. The thermal influence on the welding bath and the grain structure will be discussed. High pure laser welded Al2O3-ceramic parts of various shapes will be presented. This new method of laser welding of ceramics opens up a wide field of new application. Almost now a lot of branches of industry have already shown their interest in this promising technique. Most applications are expected with sensor elements generally, and in the protection of electronic elements against high temperatures, abrasion and/or chemical attacks.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In order to use the important properties of ceramics it is sometimes necessary to construct special geometrical forms that cannot be manufactured by conventional methods of shaping. Techniques to join parts of ceramics are often accompanied with a decrease in the material properties.We will describe an absolutely new method of a laser welding technology developed in the Laser Application Centre of Mittweida. Based on an additive-free procedure it allows us to join parts of alumina without any changes of their thermal and mechanical strengths. Two laser beams are used to avoid thermally induced stresses. Furthermore it is possible to join without furnaces and in natural atmosphere.Highly refined laser welded Al2O3- ceramic parts of various shapes will be presented and the thermal influence on the grain structure will be discussed.This new method of laser welding of ceramics opens up a wide field of new applications. A lot of branches of industry have already shown their interest in this promising technique. Most applications are expected with respect to sensor elements generally, for ceramical parts of lamps, in dental technology, and in the protection of electronic elements against high temperatures, abrasion or chemical attacks.In order to use the important properties of ceramics it is sometimes necessary to construct special geometrical forms that cannot be manufactured by conventional methods of shaping. Techniques to join parts of ceramics are often accompanied with a decrease in the material properties.We will describe an absolutely new method of a laser welding technology developed in the Laser Application Centre of Mittweida. Based on an additive-free procedure it allows us to join parts of alumina without any changes of their thermal and mechanical strengths. Two laser beams are used to avoid thermally induced stresses. Furthermore it is possible to join without furnaces and in natural atmosphere.Highly refined laser welded Al2O3- ceramic parts of various shapes will be presented and the thermal influence on the grain structure will be discussed.This new method of laser welding of ceramics opens up a wide field of new applications. A lot of branches of industry have already shown their interest in this promising technique...

Presently, there is a growing demand from the industry for microprocessing of materials. In particular, for applications in the field of microsystems technology it is necessary to produce structures with dimensions down to the micrometer scale especially in materials that could not be processed or processed well by conventional microelectronic technologies. We have been investigating the drilling of anodically bondable Pyrex glass by means of laser microprocessing using the excimer laser mask projection technique (248 or 193 nm wavelength, 10 ns pulse duration, 8 mJ pulse energy, 500 Hz repetition rate). We will show the dependence of the processing results on the laser parameters. The diameter of the holes ranges from 30 to 100 μm at the front side and from 1 to 50 μm at the rear side of the 500-μm-thick wafer. We observed the formation of cracks in the laser processed region. Accordingly, we found distinct relationships between the process parameters and the quality of the walls of the drilled holes. Especially the change from 248 to 193 nm wavelength led to a distinct decrease of crack formation but the wall at the rear side of the wafer shows still a break off of some material. As a solution the drilling of the wafer from both sides of the wafer allows us to produce crack free holes.Presently, there is a growing demand from the industry for microprocessing of materials. In particular, for applications in the field of microsystems technology it is necessary to produce structures with dimensions down to the micrometer scale especially in materials that could not be processed or processed well by conventional microelectronic technologies. We have been investigating the drilling of anodically bondable Pyrex glass by means of laser microprocessing using the excimer laser mask projection technique (248 or 193 nm wavelength, 10 ns pulse duration, 8 mJ pulse energy, 500 Hz repetition rate). We will show the dependence of the processing results on the laser parameters. The diameter of the holes ranges from 30 to 100 μm at the front side and from 1 to 50 μm at the rear side of the 500-μm-thick wafer. We observed the formation of cracks in the laser processed region. Accordingly, we found distinct relationships between the process parameters and the quality of the walls of the drilled holes. Es...

Under consideration of already published approaches, energy absorption and conversion of a laser beam penetrating into a powder layer is described as a function of grain size, grain density, laser beam intensity, and material properties. The simulations are based on a ray tracing algorithm and show typical results of the early dissipation phase regarding the energy form and the spatial distribution in the irradiated powder. An approach for the estimation of the powder layer thickness is proposed; optimum thicknesses are derived. The findings are applied to interpret observations that have been made during laser micro sintering of molybdenum powder.

We report on selective realignment of the exchange biased magnetization direction in spintronic layer stacks using rapidly deflected focused laser radiation in a direct-write technique. Laser-based magnetic field cooling by applying either pulsed or continuous wave laser radiation was investigated. The magnetic properties of laser-based field cooled layer stacks were investigated by using magneto optical Kerr effect (MOKE) measurements. The dependencies of the processing parameters peak intensity and external magnetic field strength on the resulting exchange bias field strength were evaluated. In addition, temperature field simulations gain deeper insights into the mechanisms of laser-based field cooling. Our results show significant influence of the laser processing regime. Field cooling induced by continuous laser radiation caused higher exchange bias field strengths, compared to pulsed laser radiation. Moreover, the external magnetic field strength affected the resulting exchange bias field strength only by irradiating low-intensity laser beams.

The selective ablation of 100nm thin Nickel-Chromium-alloy films on glass substrate was investigated using femtosecond laser pulses (λ=1030nm, τp=170 fs, Ep,max=7μJ). The influence of the processing parameters such as fluence, pulse number and pulse repetition rate on the ablation process was examined. Single and multiple pulses ablation thresholds of the Nickel-Chromium-alloy film were determined and the incubation coefficient calculated. Optical and electron microscopy were employed to characterize the patterned area. As a result, different irradiation morphologies were observed, dependent from the processing parameters. A processing window for film side ablation of the Nickel-Chromium-alloy film without damaging the underlying glass substrate was found, however, the edge of the ablation craters were covered with laser induced periodic surface structures (LIPSS).