On the pulse of material fabrication

Swinburne researchers studying the detailed mechanics of interactions between light and matter are making significant contributions to 3D laser printing.

Touted as the potential technology for the factory of the future, the current generation of 3D laser printers is based on the principle that a raw material, typically a powder, is converted into a solid by focused laser light. They give a tantalising glimpse of a future where high-precision products are created inexpensively on demand from digital files in comparatively tiny ‘factories’ in ordinary shop-fronts. Yet there remain many ways in which current technology could be improved if only the physics of light–matter interaction were better understood.

The work of Professor Saulius Juodkazis and his team at Swinburne’s Centre for Micro-Photonics has focused on this largely unexplored area of material science.

“One of the technological problems of the current generation of 3D laser printer is the need to add photo-initiators to the raw material to absorb laser light, since the host material on its own is transparent at the wavelength of the laser,” said Professor Juodkazis.

“But photo-initiators are toxic, which has limited the application of this technology in biomedical fields where the potential is huge.

“Our work shows that with ultrashort laser pulses, photo-initiators are not required. We can control and tailor light–matter interactions solely via the properties of light.”

By adjusting the intensity, wavelength, repetition and scan speed of the laser pulses, Professor Juodkazis’s team has been able to prove the concept on solid transparent workpieces such as polymer blocks and glass, producing high-precision pieces for microfluidic applications.

“Ultrafast laser processing has the highest precision in delivering light energy to material,” explained Professor Juodkazis. “It allowed us to tailor and structure materials from tens of nanometres in size right up to sub-millimetre size, making it unique in bridging the domains of nanotechnology, microtechnology and conventional precision material processing.”

Professor Juodkazis’s work homed in on what exactly happens when a highly focused laser pulse interacts with material at the nanometre scale. The laser irradiation spot experiences a rapid and extreme rise in temperature and pressure, which can produce exotic high-pressure material phases that sometimes last for only a fraction of a second.

“Swinburne has the only ultra-short pulse laser with industrial-grade power and repetition rate in Australia,” said Professor Juodkazis. “Based on our research and this facility, we have a number of collaborations, including with Workshop-of-Photonics in Lithuania, which started with a patent licence transfer for laser fabricated surfaces for sensors. We also work with Laser Systems in Japan on industrial laser cutting applications, and with Flewsolutions in Brisbane on sensors and laser fabrication.”

3D laser printing with light

• 3D printers start with a raw material, for laser fusing (or sintering) it’s typically a powder of either plastic or metal.

• Toxic photo-initiators, molecules that creates reactive species when exposed to radiation, are usually added to the powder to help it absorb laser light. This step can be skipped with new ultrafast laser manufacturing.

• A layer of powder is laid down

• A focused laser light fuses (or sinters) part of the layer into a solid shape in a process known as photopolymerisation.

• This process is repeated until a 3D shape is created.