A main field of application for USP lasers is the fabrication of high-precision microstructures by ablation of bulk material. In the last 10 years, the output power of USP laser systems increased from around 10 W to several 100 W. This enables the increase of productivity of USP laser ablation processes by more than one order of magnitude.
So far there is a leak of appropriate strategies and optical system to overcome limits based on heat accumulation. In this contribution, ablation strategies for steel and silicon by using far more than 100 W is deduced and presented.
In this study, an optical setup based on two phase-only spatial light modulators is presented, capable to shape two parallel laser beams. Each of the light modulators creates different and complementary Gaussian multi-spot distributions in the focal plane. By the polarization based combination of two differently shaped beams, a multi-spot beam profile with higher multi-spot density than for a single spatial light modulator setup can be obtained without speckles to appear. Beam shaping results are characterized by means of a beam profile camera and compared to a single spatial light modulator setup. Beam shapes generated by the presented setup are applied to ultrashort pulse laser ablation of metals. The potential of the presented optics is discussed regarding ground roughness and waviness of the ablated structure.
Liquid crystal on silicon phase-only spatial light modulators are widely used for the generation of multi-spot patterns. The phase distribution in the modulator plane, corresponding to the target multi-spot intensity distribution in the focal plane, is calculated by means of the so-called phase retrieval algorithms. Due to deviations of the real optical setup from the ideal model, these algorithms often do not achieve the desired power distribution accuracy within the multi-spot patterns. In this study, we present a novel method for generating high quality multi-spot patterns even in the presence of optical system disturbances. The standard Iterative Fourier Transform Algorithm is extended by means of machine learning methods combined with an open camera feedback loop. The machine learning algorithm is used to predict the mapping function between the desired and the measured multi-spot beam profiles. The problem of generation of multispot patterns is divided into three complexity levels. Due to distinct parameter structures, each of the complexity levels requires differing solution approaches, particularly differing machine learning algorithms. This relation is discussed in detail eventually providing a solution for the simplest case of beam splitter pattern generation. Solutions for more complex problems are also suggested. The approach is validated, whereby one machine learning method is successfully implemented and tested experimentally.
Part quality and building time during selective laser melting strongly correlates with the quality of the melting tracks and the melting rate respectively. Conventional processes can be improved by changing their parameters. Increase of the building rate is achieved by modifying the laser beam properties, e.g. spot size and laser power, and process parameters, such as layer thickness and scanning speed. However, process acceleration often leads to appearance of balling, spatters, evaporation and undercuts with subsequent degradation of component quality. The present investigation introduces an innovative way towards increasing of melting rate without lowering part quality. In our approach, the laser beam energy is efficiently distributed on the powder bed by means of beam splitting. This leads to the generation of high volume melt pools. Finally, an outlook on further increase of the melting rate is given.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.