The Princess Leia Project: Researchers Use Lasers to Create 3D Image Projections

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If you’re a Star Wars fan, you’ll remember the iconic scene from the very first movie where R2D2 projects an image of Princess Leia to Luke Skywalker and Ben Kenobi, in which she utters the famous phrase, “Help me, Obi Wan Kenobi, you’re my only hope.” But while many people believe the image of the crouching Leia is a hologram, it is actually a volumetric image: a 3D image that floats in midair, which you can walk around and see from every angle. Other famous examples include the massive image-projecting table in Avatar and the 3D displays Tony Stark interacts with in the Iron Man movies.

It is this last example that ultimately inspired science fiction fan, holography expert, and Brigham Young University (BYU) electrical and computer engineering professor Daniel Smalley’s latest research project.

Dr. Smalley with his student researchers. [Image: BYU]

“There was an epiphanic experience that happened, at the beginning of all of this. I was in the Iron Man movie, and there’s a scene where the protagonist, Tony Stark, sticks his arm inside an ostensibly holographic gauntlet. And when I saw that, before seeing that scene, I had believed that holography could do anything. But when I saw that, I realised it couldn’t, because as he sticks his hand over the lit-up table, now he’s blocking the light. So how then is that appearing above his hand?” Smalley explained.

“When I saw that film, I thought the only way you could make that display was with something like floating nanobots shooting lasers. And it’s interesting, now, that we’ve happened upon a way that’s not dissimilar to that idea.”

A freezeframe of the OTD tracing out a spiral image in real time, above a researcher’s finger. [Image: Nature]

Smalley has long wanted to create the same type of 3D image projection, and worked with his researchers to make the 3D displays of science fiction real. The first creation of a free-space volumetric display, which can reproduce full-color graphics in mid-air that are visible from every angle, is detailed in a paper, titled “A photophoretic-trap volumetric display,” recently published in Nature.

Smalley said, “We refer to this colloquially as the Princess Leia project.”

The team has named the technology optical trap display, or OTD, and it projects graphics into the air, so they can be seen from all angles.

“You capture a particle in an invisible, or almost invisible ‘tractor beam’, then you drag that around to every point of an image,” explained Smalley, who is also the lead author of the paper. “When it’s in the right place, you shoot it with red, green and blue lasers to make it illuminate, and build up an image point by point, dragging this cellulose particle around as you go.”

A simple wireframe image created using the OTD technology. [Image: Nature]

A holograph only scatters light at a 2D surface, so you won’t see a 3D image if you’re not looking directly at that surface. But a volumetric display contains multiple scattering surfaces throughout the same 3D space that’s occupied by the image. If you’re looking at the image, you’re also seeing the scatters, which is why volumetric images can be seen from all angles. The researchers developed the platform together, which is based on photophoretic optical trapping and can produce aerial, full-color volumetric images, with 10-micron points, by persistence of vision.

According to Smalley, the simplest way of understanding their project is to think of the images as objects 3D printed at extremely high speeds, with the tiny glowing particle making a visual image as it moves.

“This display is like a 3D printer for light. You’re actually printing an object in space with these little particles,” Smalley said.

The OTD technology may call to mind Ekaggrat Singh Kalsi’s work with 3D light printing, but the two are very different.

A long-exposure image created with the OTD technology. [Image: Nature]

Smalley said, “We’re providing a method to make a volumetric image that can create the images we imagine we’ll have in the future.”

Other researchers have worked to create volumetric imagery, but Smalley’s team is the first to develop the novel method of using optical trapping to capture particles and illuminate them with different colors of lasers. The only issue now is that the images they’re creating either take a long time to create, or are very small – a simple spiral is only a couple of millimeters high and only barely visible to the naked eye. The above image of one of the researchers posing in a similar way to Princess Leia is far more detailed, but could only be photographed with a long exposure, and 40 seconds passed before the image was fully traced out.

But Smalley says there are options to get past this problem, such as introducing a higher number of particles to each display or constantly reintroducing new particles when old ones get lost.

“After all, these are as cheap as, literally, dirt,” Smalley said.

He believes it’s worth it to continue developing the technology, as his team’s technique can impart properties to the display that other 3D displays cannot achieve.

Smalley said, “The breakthrough here, I think, is to create a 3D display platform that is capable of creating the images of science fiction.”

In addition, the innovative 3D technology could one day even have applications in the aviation and medical fields.

Discuss this and other 3D printing topics at or share your thoughts below. 

[Sources: The Guardian, Brigham Young University]


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