Conference Agenda

Lasers emitting short pulses, with wavelengths ranging from UV to NIR have been demonstrated to be effective to remove debris or contamination deposited on the architectonic elements, such as graffiti, patinas, black crusts and chewing gum. Here, we present an alternative laser cleaning method to remove chewing gum encrustations on natural stone, based on the use of a continuous wave, low power CO2 laser. The encrustations of chewing gum are mainly composed of their rubber or elastomer components which strongly absorb the CO2 laser radiation. Additionally, we propose a method for rapid assessment of the cleaning level based on hyperspectral reflectance imaging. The results obtained have been confirmed using characterization techniques commonly used in the cleaning level determination: stereomicroscopy, profilometry, Raman spectrometry and Fourier-transform infrared spectroscopy. This non-invasive method of cleaning control will allow real-time control of the cleaning process, avoiding over-cleaning or insufficient cleaning.

Goal of the investigations was to develop a laser-based, additive-free joining process for cellulose-based materials such as paper and cardboard. Previous investigations have shown that paper quickly transforms into liquid and gaseous reaction products when irradiated with CO laser radiation, which can be used for joining in a heat-sealing process.

In the current project, the process is being further developed with a view to increasing the joint strength and using standard industrial papers. Laser parameters and paper materials were varied and the influence on the joining result and the chemical material conversion was analysed. It was possible to realise joints whose strength was hig-her than that of the paper material itself.

The process will be implemented in a demonstrator plant with the aim of producing product packaging. A major advantage of the process is the water-solubility of the paper's own adhesive, which does not impair the recyclability of the paper.

Thermoplastic coatings are highly valued in various industries for their ability to protect surfaces against corrosion and minimize excessive wear. Laser-based directed energy deposition of polymers (DED-LB/P) represents a promising method in this respect, offering the ability to realize partial coatings, selectively adjustable layer thicknesses and structure widths, and beyond that, complex three-dimensional structures. In the present study, a common directed energy deposition machine equipped with a high-power diode laser (Pmax = 4 kW), a rotating plate powder feeder and a discrete coaxial powder nozzle was used to produce carbon black/polyamide 11 coatings on metallic substrates. The high laser power available for polymer processing allows a large laser beam diameter (d = 10 mm) to be set, resulting in a high deposition rate and improved powder catchment efficiency. The coatings produced are evaluated for surface quality, density, and bonding defects to verify their performance and reliability.

In this work, we explore the use of a femtosecond laser operating in the GHz burst regime for metal polishing, both with and without ablation, to enhance micromachining quality. The high number of pulses per burst (800 ppb) combined with high burst repetition rate (800 kHz) allows for ideally distributing the laser energy over metallic samples. As surface melting and smoothing is driven by surface tension forces, this is a critical factor in this process. Recent studies have demonstrated that GHz bursts of femtosecond pulses are particularly effective for metal polishing, as the pulse-to-pulse delay within the burst is shorter than the material's characteristic heat relaxation time. We will present our results on stainless steel and titanium and point out the best process windows.

Laser polishing of metals is a multi-step process requiring detailed and individual parameter optimization for each processing step. The experimental approach to parameter optimization for new materials and initial surface roughnesses is not optimized itself. Therefore, high numbers of experiments are necessary. Furthermore, established approaches neglect that laser polishing is a multi-step process, resulting in redundant experiments and suboptimal roughness. In this work, a new approach for optimizing and benchmarking the parameter optimization process is developed. This approach is based on experiment simulation using a dataset of 2,600 conducted experiments on laser polishing of 1.2343. Thereby, it allows for cost-free optimization and comparison of parameter optimization strategies. In the benchmark a wide range of conditions such as experiment limitation and target roughness were tested. As a result, the domain-based approach could find parameters meeting the criteria in less than 100 experiments even for a suboptimal choice of initial algorithm values.

Laser-based optical manufacturing enables efficient production of high-precision optical components through processes like selective laser etching (SLE), laser ablation, and laser polishing (LP). At the Institute of Microtechnology and Photonics (IMP), we focus on combining SLE with laser polishing for miniaturized optics. Studies show that the one-shot LP strategy outperforms scanning LP by preventing mid-spatial frequencies. However, achieving uniform polishing remains challenging due to the Gaussian beam profile, which causes uneven polishing across the lens surface. While diffractive optics can improve power distribution, they are costly and often differ in practice. We present a novel approach called Quasi-Beamforming, utilizing galvanometric scanners to create a tailored thermal distribution for uniform polishing. This strategy is demonstrated on a convex, rotationally symmetric surface, applying a “sombrero” thermal profile to achieve smooth, high-quality optics.