Laser-based 3D printing: tool for the further development of optical microscopy

Optical microscopy is a widely used method for examining objects, organisms and surfaces on a small scale. However, its lateral resolution is limited by light diffraction, which is becoming increasingly problematic with conventional lenses as the demand for higher resolutions grows.

In a new publication in “Light: Advanced Manufacturing”, researchers from the Institute of Electron Structure and Lasers, the University of Helsinki and Ruhr-Universität Bochum have developed a new strategy for producing high-quality microspheres using laser-based 3D printing technology. This approach uses multiphoton lithography (MPL), which enables maskless production of real 3D structures in the micro and nano range. Due to the non-linear nature of MPL, precision can be significantly increased by locally adjusting the laser intensity during the printing process.

By combining this approach with an advanced layering and slitting strategy, the team succeeded in producing a microsphere with a diameter of 20 µm and near-perfect geometrical quality (λ/8) as well as exceptional surface smoothness. This microsphere was printed on a cover glass with a central hole that was processed by femtosecond laser ablation. The combination of this modified cover glass with the microsphere results in a 3D microdevice.

The performance of the microsphere in this 3D microdevice was tested using a Mirau Coherence Scanning Interferometer (MCSI) and a calibration grid with a resolution of λ = 0.28. The optical quality of the sphere exceeded the typical resolution limits of conventional lenses in visible light, while the high axial resolution of the MCSI was maintained.

The sphere, including the modification of the cover glass, was manufactured in just eight minutes. The unique capabilities of the MPL also enable the exploration of innovative micro-optical structures and systems to further improve lateral resolution for 2D and 3D optical microscopy. In the future, the researchers see great potential in using the MPL to develop cost-effective customized devices that can improve the resolution of any optical microscope.