When most people think of 3D printing, they likely picture a relatively chunky object being built from the bottom up, one layer at a time. A new technique, however, allows much more intricate items to be produced – and it does so by changing the color of laser light.
Currently being developed by a team at Stanford University, the process is a variation on what is known as volumetric 3D printing.
Putting it simply, that type of printing involves shining beams or patterns of light through the transparent top and sides of a container, inside of which is a photosensitive gelatinous resin. Wherever that resin is exposed to the light, it polymerizes (solidifies) – the rest of the resin in the container remains a gel.
By moving the light source around, so it reaches different parts of the resin, it's possible to gradually build up a three-dimensional object. That item stays suspended in the gel, until it's finally fished out.
Stanford's "triple fusion upconversion" technique builds upon an existing sub-type of volumetric 3D printing – called two-photon absorption – which is utilized to create particularly detailed objects.
The new process involves using high-energy blue laser light to polymerize the resin in highly precise locations. However, if one continuous beam of that light were to be shone into the container, the resin would solidify along that beam's entire length. To get around that problem, the beam starts out as low-energy red laser light, and only becomes blue at the point at which it's focused.
In order for that to happen, tiny silica-coated droplets of special nanomaterials are dispersed throughout the resin. Wherever the red light is focused onto these droplets, a chain of energy transfers occurs, ultimately converting that light's low-energy red photons into high-energy blue ones. As a result, the resin polymerizes at that exact point.
"Traditional two-photon printing will look very similar to what we're doing here […] however the physical process requires a huge amount of laser power to run, and thus is typically confined to small (nano to micro) scales," lead scientist Asst. Prof. Dan Congreve told us. "Our process needs much, much less power (we only used 4 milliwatts, which is less than a typical laser pointer), so we can do it at a larger (~cm) scale."
Congreve and colleagues are now looking into speeding up the printing process – possibly by using multiple lasers simultaneously – plus they're exploring the use of triple fusion upconversion in more efficient solar panels, which could convert low-energy light into usable higher-energy wavelengths.
The research is described in a paper that was recently published in the journal Nature.
Source: Stanford University
