01 Dec 2021
3D Matter Made to Order cluster shows how 3D nanostructures can be more economically printed by desktop devices.
Now researchers at Karlsruhe Institute of Technology (KIT) and Heidelberg University, both in Germany, are using a different process for this purpose: two-step absorption works with inexpensive and small, blue laser diodes. As a result, much smaller printers can be used, say the developers.
The work is reported in Nature Photonics.
Presently, laser printing is the method of choice for additive manufacture by 3D printing, says the KIT team, because it offers the best spatial resolution of all methods and reaches an extremely high printing speed. In laser printing, a focused laser beam is directed towards a light-sensitive liquid.
At the focal point, the laser light turns a switch in special molecules and triggers a chemical reaction. The reaction leads to the local hardening of the material. By moving the focal point, any 3D micro- and nanostructures can be produced.
The chemical reaction is based on so-called two-photon absorption, meaning that two photons excite the molecule at the same time, which causes the desired chemical modification. However, this simultaneous excitation happens very rarely, which is why complex pulsed laser systems have to be applied, resulting in bigger dimensions of the laser printer.
When using the so-called two-step process, more compact, smaller printers can be realized. The first photon transfers the molecule to an intermediate state. In the second step, a second photon transfers the molecule from the intermediate state to the desired excited state and starts chemical reaction.
The advantage: contrary to two-photon absorption, the absorption of the two photons does not necessarily have to happen simultaneiusly. “For the process, compact and low-power continuous-wave laser diodes can be used,” commented Vincent Hahn, the first author of the study from KIT’s Institute of Applied Physics (APH).
The required laser powers are far below those of conventional laser pointers. Printing, however, requires specific photoresists. “Development of these photoresists has taken several years and has been possible only in collaboration with chemists,” said Professor Martin Wegener, APH.
“The publication reveals that the idea works, even better than the previously demonstrated two-photon absorption,” said Hahn. To Wegener, the advantage is obvious: “It is a big difference between using a femtosecond laser as large as a big suitcase for several tens of thousands of euros or a semiconductor laser that is as large as a pinhead and costs less than ten euros.
“Now, the other components of the 3D laser nanoprinter also have to be miniaturized. To me, a device that will be as large as a shoebox appears realistic in the next years. That would be even smaller than the laser printer on my desktop at KIT,” he added.
By this means, 3D laser nanoprinters could become affordable for many groups, leading to what the KIT team describes as “a democratization of 3D laser printing technology.” Besides the KIT researchers, scientists from Heidelberg University were involved in the publication. The publication originated within the framework of the joint Cluster of Excellence known as 3D Matter Made to Order from KIT and Heidelberg University.
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