The lasers in today's laser printers for paper printouts are tiny. In contrast, 3D laser printers, which print three-dimensional micro- and nanostructures, have so far required large and expensive laser systems. Researchers at the Karlsruhe Institute of Technology (KIT) and Heidelberg University are now using a different process instead. Two-stage absorption works with tiny blue laser diodes, which are inexpensive. This makes it possible to work with much smaller printers. The researchers report on their work in the journal Nature Photonics.(DOI: 10.1038/s41566-021-00906-8)
Laser printing is currently the process of choice for additive manufacturing with 3D printing, as it offers the best spatial resolution of all processes and at the same time an extremely high printing speed. In laser printing, a focused laser beam is directed at a light-sensitive liquid. At the focal point, the laser light flips a switch in special molecules, as it were, which triggers a chemical reaction. This leads to a local solidification of the material. Any micro- and nanostructures can be produced by shifting the focal point. The chemical reaction is caused by so-called two-photon absorption, i.e. two light particles (photons) excite the molecule simultaneously, which causes the desired chemical change. However, this simultaneous excitation is extremely rare, which is why complex pulsed laser systems have to be used, which in turn results in larger dimensions for the laser printer.
More compact 3D printers thanks to two-stage process
In contrast, smaller, more compact printers are possible with the so-called two-stage process. In this process, the first photon puts the molecule into an intermediate state. In the second stage, a second photon brings the molecule from the intermediate state to the desired final state - and starts the chemical reaction. The advantage: this does not have to happen simultaneously, as is the case with two-photon absorption. "This is why the process works with compact and low-power continuous wave laser diodes," explains Vincent Hahn, first author of the publication, from the Institute of Applied Physics (APH) at KIT. The laser power required for this is even significantly lower than that of commercially available laser pointers. However, specific photoresists must be used for this printing process. "The development of these photoresists took several years and was only possible thanks to collaboration with chemists," explains Professor Martin Wegener from APH.
Not just simpler, but even better
"In the publication, we show that the idea works, and even better than with the two-photon absorption previously used," says Hahn. For Wegener, the advantage in the application is obvious: "It makes a considerable difference whether you need a box-sized femtosecond laser for several tens of thousands of euros or a pinhead-sized semiconductor laser for less than ten euros. The next step is to miniaturize the other components of the 3D laser nanoprinter. A device the size of a shoebox seems quite realistic to me in the next few years. That would be even smaller than the laser printer on my desk at KIT." This means that 3D laser nanoprinters could suddenly become affordable for many groups. Experts are already talking about the democratization of 3D printing technology.
In addition to the KIT researchers, scientists from Heidelberg University were also involved in the publication. The publication was produced as part of the joint Cluster of Excellence "3D Matter Made to Order" of KIT and Heidelberg University.
Cluster of Excellence "3D Matter Made to Order"
In the Cluster of Excellence 3D Matter Made to Order (3DMM2O), scientists from the Karlsruhe Institute of Technology and Heidelberg University are conducting interdisciplinary research into innovative technologies and materials for digital and scalable additive manufacturing processes in order to make 3D printing more precise, faster and more efficient. The aim is to fully digitize 3D manufacturing and material processing from the molecule to the macrostructure. In addition to funding as a Cluster of Excellence within the Excellence Strategy of the German federal and state governments, 3DMM2O is also funded by the Carl Zeiss Foundation.
