s a spinoff of the Laser Research Centre of Vilnius University (Lithuania), the experts at Femtika research and develop 3D laser precision micromachining, specialising primarily in hybrid
micromachining technologies. It produces, for example, universal tools with femtosecond lasers suitable for multiphoton polymerisation, laser ablation and selective laser etching technologies. The company has specified linear stages and galvo scanners from
Aerotech since it was founded in 2013, and so the heart of a laser nanofactory workstation always consists of a femtosecond laser in combination with a nanopositioning system from Aerotech. These are used to enable fast and highly precise 3D manufacturing across the entire workspace. The company used to assume that nanometre precision could only be
achieved with piezo stages, but it then tried Aerotech’s high-precision linear stages, which immediately improved the quality for larger microstructures and also allowed them to be manufactured faster – by at least a factor of 10. It soon became clear that the speed could be increased by a further factor of 10 if an Aerotech AGV galvo scanner was added.
One of Femtika’s most commonly used processes is multiphoton polymerisation, a high resolution 3D printing technology. This is based on photopolymerisation reactions that are triggered only in a focal volume of the sharply focused femtosecond laser focal point. The microstructures are printed by scanning the laser beam over the volume of the photopolymer. This has the ability to print very high resolution of structure sizes
down to 150nm, with an exceptionally high surface quality and the ability to create 3D micro objects of any shape without the need for supports. Examples of its applications are micro-optical and photonic elements, which are not only printed on planar surfaces but also directly on fibre tips, photodiodes, semiconductor ICs, etc. The process is also used for biomedical applications such as the production of 3D scaffolds, which are support structures for cell growth that can be used for drug testing. Femtika’s laser nanofactory machines also offer many other
microfabrication techniques made possible by femtosecond lasers. This means that the same machine can perform a variety of processes that would not be possible in the traditional 3D printing world. Its workstations are often used for selective laser etching of glass. Unlike 3D printing, this is a subtractive process where the laser is used to modify the intermolecular glass structure. The laser-modified glass areas are then chemically etched away, leaving only unmodified areas. This is not only applied in medical technology (in microfluidic devices or micromechanical particles, for example) but also in microrobotics and the watch industry. “In general, lasers are unique tools because of their ability to modify
the volume of transparent materials without touching their surface,” explained Dr. Vytautas Purlys, CTO at Femtika. By modifying the volume of materials, different waveguides, diffractive optical elements or Bragg gratings can be realised. Surfaces can also be modified with femtosecond lasers. For example, microablation is used when tiny grooves or holes are needed on the surfaces, while surface structuring enables the production of hydrophilic or hydrophobic surfaces. Each laser process places its own unique demands on the positioning
system. Some processes require precision and resolution, others speed, others a working range, and all this together results in quite a demanding list of requirements. The specifications of the positioning system directly contribute to the quality of the manufactured structures. Stitching together small areas to create a larger part is one of the most
essential aspects in the world of submicrometer printing. Stitching errors can be caused by inaccuracies of the positioning system, but also by the material’s behaviour. In the micro world, problems are caused by the way the materials react to the laser pulses. Often the galvo scanners are used to raster the laser spot over small square areas, which are then joined by repositioning them in steps, leading to errors in the joining process. This approach can significantly affect the quality of the manufactured structures. For example, microlenses manufactured in this way show considerable scattering, micro parts can contain fractures, and parts for the watch industry lose their aesthetic appeal. “To minimise the number of stitching errors, we actively use infinite-field-
of-view technology, where the movement is automatically divided into a fast and a slow movement and executed simultaneously with Aerotech’s
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galvo scanners and linear tables respectively,” explained Purlys. “In this way, the stitching is eliminated and the structures produced become more uniform.”
The system’s overall precision is limited by the least precise component, so the performance of the stages and galvos must be precisely matched. The control system is, however, also important. With direct laser writing techniques, the structures are written while the
table/galvo scanner is moving. When the positioning system is accelerating or decelerating, the number of laser pulses hitting the material increases. This can lead to various errors or even material damage in these areas. These problems can be solved by firing the laser pulses at constant distances from each other. If both galvo scanners and mechanical tables are used, this poses a challenge for the control system as the positions of both devices have to be taken into account. “As longtime users of Aerotech’s A3200 controller, we were excited to be
able to test the new Automation1 control platform as well,” explained Purlys. He added: “Apart from the significant improvements to the user interface, we also discovered many new useful features. For example, the way the movement is defined is now much more user-friendly, the control parameters are easier to find and their meaning is now also easier to understand. From the integrator’s point of view, we like the new control API, which makes the implementation of various control functions much easier.”
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