Using ultra-short laser pulses for the generation of microstructures results in a high flexible tool for free form geometries in the micro range. Increasing laser power and repetition rates increase as well the demand of high flexible and efficient process strategies. To increase the ablation efficiency the optimal fluency can be determined, which is a material specific value. By varying the beam shape, the ablation efficiency can be enhanced. In this study a deformable mirror was used to vary the beam shape. This mirror is built by combining a piezo-electric ceramic and a mirror substrate. The ceramic is divided into several segments, which can be controlled independently. This results in a high flexible deformable mirror which influences the beam shape and can be used to vary the spot size or generate line geometries. The ablation efficiency and roughness of small generated cavities were analyzed in this study as well as the dimensions of the cavity. This can be used to optimize process strategies to combine high volume ablation and fine detail generation.
Using ultra-short laser pulses for micro structuring or drilling applications reduces the thermal influence to the surrounding material. The best achievable beam profile equals a Gaussian beam. Drilling with this beam profile results in cylindrical holes. To vary the shape of the holes, the beam can either be scanned or – for single pulse and percussion drilling – manipulated by masks or lenses. A high flexible method for beam shaping can be realized by using a deformable mirror. This mirror contains a piezo-electric ceramic, which can be deformed by an electric potential. By separating the ceramic into independent controllable segments, the shape of the surface can be varied individually. Due to the closed surface of the mirror, there is no loss of intensity due to diffraction. The mirror deformation is controlled by Zernike polynomials and results e.g. in a lens behavior. In this study a deformable mirror was used to generate e.g. slits in thin steel foils by percussion drilling using ultra-short laser pulses. The influence of the cylindrical deformation to the laser beam and the resulting geometry of the generated holes was studied. It was demonstrated that due to the high update rate up to 150 Hz the mirror surface can be varied in each scan cycle, which results in a high flexible drilling process.
The use of picosecond lasers for microstructuring, especially in the combination with scanner optics, leads to undesired
effects with increasing ablation depths. The cavity edges slope to a degree ranging between 50° and 85°, depending on
the material. With highly reflective substrates, ditches of up to 20% of their total depth can be formed on its ground
structure. In certain materials also diverse substructures such as holes, canals, or grooves can be developed. These could
impact the precision of the ablation geometry partially. A systematic study of the specific ablation characteristics is
needed to achieve a defined depth of the structure. Considering a huge number of influential parameters, an automation
of such measurements would be meaningful. For a study of eight different materials (high-alloy steels, copper, titanium,
aluminum, PMMA, Al2O3 ceramics, silicon and fused quartz), an industrial ps-laser coupled with a chromatic sensor for
distance measurement was used. Hence a direct acquisition of the generated structures as well as an automatic evaluation
of the parameters is possible. Furthermore an online quality control and a local post processing can be implemented. In
this way the generation of complex structures with a higher precision is possible.