Process to enable more compact & affordable 3D nanoprinters

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Electron microscopic reconstruction of a 3D nanostructure printed with the two-step absorption process (left) and light microscopy (right). (Image: University of Heidelberg/KIT)

Scientists have developed a process that could enable 3D laser nanoprinters to be dramatically reduced in size.

Reported in Nature Photonics, the process can be performed using small, inexpensive blue laser diodes, saving the need for bulky, expensive femtosecond lasers.

When 3D laser printing structures on the micro- and nanoscale, a focused laser beam is directed towards a light-sensitive liquid. At the focal point, the laser light triggers a chemical reaction within the molecules of the liquid. The reaction leads to the local hardening of the material, and by moving the focal point, any 3D micro- and nanostructures can be produced.

The chemical reaction is based on two-photon absorption, a process where two photons excite a molecule at the same time to cause the desired chemical modification. However, due to this simultaneous excitation happening very rarely, complex, bulky ultrashort pulsed laser systems must currently be used to facilitate it, resulting in laser printers with larger dimensions and higher price tags.

Now, however, researchers of Karlsruhe Institute of Technology (KIT) and the Heidelberg University have developed another process for this purpose. Known as two-step absorption, the process can be done with small, inexpensive blue laser diodes.

As opposed to two-photon absorption, where two photons must excite a molecule at the same time, two-step absorption instead comprises an initial photon transferring the molecule to an intermediate state, with a second photon then transferring the molecule to the final, desired excited state, starting the chemical reaction.

As the process doesn’t require two photons to hit a molecule simultaneously, an ultrashort pulse laser is no longer required to facilitate it. 

'For the process, compact and low-power continuous-wave laser diodes can instead be used,' confirmed Vincent Hahn, the first author of the Nature Photonics study from KIT’s Institute of Applied Physics (APH). 

While the required laser powers are far below those of conventional laser pointers, the process does require specific photoresists developed by the researchers in order to work. 'Development of these photoresists has taken several years and has been possible only in collaboration with chemists,' said Professor Martin Wegener, also of KIT’s APH.

According to the researcher’s their process works even better than two-photon absorption.

‘It is a big difference between using a femtosecond laser as large as a big suitcase for several ten thousand euros, or a semiconductor laser that is as large as a pinhead and costs less than ten euros,’ said Wegener. ‘Now, the other components of the 3D laser nanoprinter also have to be miniaturised. 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.’ 

In doing this, the researchers believe 3D laser nanoprinters could become more affordable.

The work was done within the framework of the joint Cluster of Excellence ‘3D Matter Made to Order’ (3DMM2O) of KIT and Heidelberg University. Within the cluster, scientists of KIT and Heidelberg University conduct interdisciplinary research into innovative technologies and materials for digital scalable additive manufacturing to enhance the precision, speed, and performance of 3D printing.

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