Light can not only be used to measure, heat and remove material, it can also be used to create structures. The two most common processes are laser sintering or laser stereolithography, in which a 3D structure is created layer by layer. During sintering, powder is heated locally using a laser beam until it melts in a targeted manner.
Macro Laser Stereolithography (SLS for short)
Laser stereolithography is based on a photochemical process in light-curing plastics. This requires far less laser power than a sintering process, but the laser should have a very short wavelength. In the past, HeCd lasers with a wavelength of 325 nm were primarily used for this purpose. However, resin suppliers are increasingly relying on the newer 355 nm solid-state lasers as they become more durable, more compact and cheaper. This means that many machines have to be converted from the old HeCd gas lasers to 355 nm. In collaboration with Mr. Resch from NRU GmbH, we tested and evaluated a new generation of UV lasers for SLS. With the converted SLS machine, objects with a size of up to 40 x 35 cm can be built using the rapid prototyping process with a layer thickness resolution of up to 0.01 mm.
Micro laser stereolithography (µSLS for short)
The µSLS is based on two-photon absorption and is also called two-photon polymerization. Short pulse lasers with 1064 or 532 nm are required for this process. The nonlinear process effectively uses only a small portion of the focus diameter, creating structures with smaller resolutions than would normally be possible due to the diffraction limitation of the laser. With the chess piece (see top right), Mr. Engelhardt from the Fraunhofer Institute ILT showed that structures in the sub-µm range can be created with our laser.
Applications in biomedicine are particularly interesting here. For example, the smallest pumps and motors in the µm range can be implemented. Furthermore, growth aids for cells can be created. A support structure (see bottom left) is made from a polymer using the µSLS process, on which a protein then grows. Cells can now attach, grow and be examined on this artificially created protein structure.
