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Painting with light in three dimensions


A new technique uses photoswitch molecules to create three-dimensional images from pure light. Joel F. Hooper reports.


A three-dimensional pyramid made of glowing rhodamine molecules.
A three-dimensional pyramid made of glowing rhodamine molecules.
Alexander Lippert

Those of us who grew up watching science fiction movies and TV shows imagined our futures to be filled with marvellous gadgets, but we’ve sometimes been disappointed when science fails to deliver. We can’t take a weekend trip to Mars yet, and we’re still waiting for hoverboards that actually hover.

But in the case of 3-D image projection, the technology used by R2D2 in Star Wars is making its way into reality. Using advances in fluorescent molecules that can be switched on by UV light, scientists at Southern Methodist University in Dallas have created a method for producing images and animations by structuring light in 3-dimentions.

The technology uses a solution of fluorescent molecules called rhodamines, which have the potential to emit visible light when they are excited by a light beam of the right wavelength. But these molecules are usually in an inactive state, and must be “switched on” by UV light before they can become emitters. When a UV light or visible light beam alone shines through the solution, the rhodamines to not emit light. But where these two beams intersect, the emitting molecules are both switched on and excited, and can produce a small glowing 3D pixel, known as a voxel.

When a number of voxels are produced at once, using two projectors positioned at 90° to a flask containing a solution of the fluorescent molecules, a 3D image is produced.

“Our idea was to use chemistry and special photoswitch molecules to make a 3D display that delivers a 360-degree view,” says Alexander Lippert, lead author of the study. “It’s not a hologram, it’s really three-dimensionally structured light.”



The team wanted to use the display for video or other animation, but creating a fast on/off cycle for the fluorescent molecules at firstproved difficult. The molecules could be switched on quickly with UV light, but returning to the off position is a process driven by heat it happened too slowly at room temperature.

The researchers found that adding a small amount of a chemical base called triethylamine, sped up the process significantly. This allowed for voxels to be produced with 33-millisecond resolution, making smooth 3D animation possible.

So far, this method is only able to produce images in a single colour, but the researchers hope to achieve full colour by mixing molecules that produce red, green and blue light.

It’s hoped that this technology will find its way into medical displays, military applications and entertainment. For sci-fi fans, its further proof that Star Wars was way ahead of its time.

Joel Hooper is a senior research fellow at Monash University, in Melbourne, Australia.
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