Mechanical polishing of glass is a time consuming process especially for lenses deviating from spherical surface such as aspheres. With laser polishing, the processing time can be significantly reduced and the wear of hard tooling can be avoided. Using laser radiation for polishing, a thin surface layer of the glass is heated up just below evaporation temperature due to the interaction of glass material and laser radiation. With increasing temperature, the reduced viscosity in the surface layer leads to the reduction of the roughness due to the surface tension. Hence, a contactless polishing method can be realized nearly without any loss of material or need of polishing agent. In this paper, results for laser polishing of fused silica, BK7, and S-TIH6 are presented with area rates up to 5 cm2/s. However, the results show that the achieved roughness with laser polishing is strongly influenced by the thermal properties of the type of glass. During laser polishing, the glass material is relocated at the surface, thus no shape errors can be corrected. To reduce the residual waviness and shape errors after laser polishing, the authors investigated a further laser-based process step (laser beam figuring, LBF) which ablates material for a shape correction. Ablation depths <5 nm allow a high precision laser ablation for selective processing. For both processes, a CO2 laser is used

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Laser polishing is a technique for smoothing the surface of metallic substrates. The roughness after polishing does not only contain remains of the initial surface roughness, it also contains new roughness due to surface structures, which are introduced by the polishing process. Since these structures greatly contribute to the roughness, it is necessary to understand the mechanisms that lead to their formation so as to prevent the structures from forming and allow higher smoothing of the surface. Hence, in this publication it is investigated experimentally and numerically why these structures occur, what the influencing parameters are and how their influence on the roughness can be reduced, for both laser macro and laser micro polishing. It could be seen that the structures are influenced by the process parameters and the material of the workpiece. For a low surface roughness, the process parameters have to be adapted antithetically in some cases which means that it is not possible to prevent all structures at the same time and that surface structures will always occur during laser polishing. The process parameters must be adapted in such a way that all structures together lead to a surface roughness as low as possible.

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A new approach to polish metallic freeform surfaces is polishing by means of laser radiation. In this technology a thin surface layer is molten and the surface tension leads to a material flow from the peaks to the valleys. No material is removed but reallocated while molten. As the typical processing time is 1 min/cm² laser polishing is up to 30 times faster than manual polishing. Reducing the roughness by laser polishing is achieved for several different materials such as hot work steels for the die and molding industries or titanium alloys for medical engineering. Enhancing the appearance of design surfaces is achieved by creating a dual-gloss effect by selective laser polishing (SLP). In comparison to conventional polishing processes laser polishing opens up the possibility of selective processing of small areas (< 0.1 mm²). A dual-gloss effect is based on a space-resolved change in surface roughness. In comparison to the initial surface the roughness of the laser polished surface is reduced significantly up to spatial wavelengths of 80 microns and therefore the gloss is raised considerably. The surface roughness is investigated by a spectral analysis which is achieved by a discrete convolution of the surface profile with a Gaussian loaded function. The surfaces roughness is split into discrete wavelength intervals and can be evaluated and optimized. Laser polishing is carried out by using a special tailored five-axis mechanical handling system, combined with a three axis laser scanning system and a fibre laser.

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This study presents the development of post-processing steps for microfluidics fabricated with selective laser etching (SLE) in fused silica. In a first step, the SLE surface-even inner walls of microfluidic channels—can be smoothed by laser polishing. In addition, two-photon polymerization (2PP) can be used to manufacture polymer microstructures and microcomponents inside the microfluidic channels. The reduction in the surface roughness by laser polishing is a remelting process. While heating the glass surface above softening temperature, laser radiation relocates material thanks to the surface tension. With laser polishing, the RMS roughness of SLE surfaces can be reduced from 12 µm down to 3 nm for spatial wavelength λ < 400 µm. Thanks to the laser polishing, fluidic processes as well as particles in microchannels can be observed with microscopy. A manufactured microfluidic demonstrates that SLE and laser polishing can be combined successfully. By developing two-photon polymerization (2PP) processing in microchannels we aim to enable new applications with sophisticated 3D structures inside the microchannel. With 2PP, lenses with a diameter of 50 µm are processed with a form accuracy rms of 70 nm. In addition, this study demonstrates that 3D structures can be fabricated inside the microchannels manufactured with SLE. Thanks to the combination of SLE, laser polishing and 2PP, research is pioneering new applications for microfluidics made of fused silica

Conventional surface structuring processes often share two crucial disadvantages. First, after the structuring process itself, some kind of surface finishing is often needed, based on another technology, which means a substantial additional expense. Second, all conventional surface structuring processes are based on the removal of material, which is wasted without any further use during processing. A new approach of structuring metallic surface structuring by laser remelting (WaveShape). In this process, no material is removed but reallocated while molten. This structuring process is based on the new active principle of remelting. The surface structure and the microroughness result from a laser-controlled self-organization of the melt pool due to surface tension. Up to now, basic research has been focused on hot work steel 1.2343 (AISI: H11), and promising results have been achieved for this material. Current research and development are now seeking to expand the spectrum of processable materials. Since remelting is a thermally driven process, significant differences between metallic materials are expected due to their thermo physical properties such as thermal conductivity, absorption coefficient, viscosity, and heat capacity. The titanium alloy Ti6Al4V has a wide range of industrial applications, especially for aviation, aerospace, and medical engineering. The WaveShape process for this material will be investigated within this paper. The procedural principle of surface structuring by remelting is based upon a sinusoidal modulation of laser power while the laser beam is moved over the surface. The lower process limit of laser power is the power required to melt material and, therefore, create a melt pool. In this context, the upper process limit of laser power is the point just before substantial amounts of the molten material are evaporated. We used metallographic cross sections to measure the dimensions of melt pool depth and width as they depend on procedural parameters, such as laser beam diameter (125-500 lm), scanning velocity (25-200 mm/s), and laser power (20-400 W). We also investigated basic interdependencies between structural characteristics (e.g., height) and procedural parameters used, such as laser beam diameter, laser power, and wavelength of modulation. The results show that the WaveShape process is well suited to process titanium alloy Ti6Al4V since structures and process velocities achieved are significantly higher than for the previously investigated hot work steel. V C 2015 Laser Institute of America. [http://dx