A novel technology uses a special class of photoactivatable molecules and digital light processing (DLP) to construct light shapes into animated structures that have volume and are viewable from 360 degrees. The technology is not a hologram, and differs from 3D movies or 3D computer design. The set-up for the 3D Light PAD includes this UV projector as well as a visible projector. They project patterns of light into a chamber of photoactivatable dye. Wherever the UV light intersects with the green light it generates a 3D image inside the chamber. Courtesy of SMU. “When you see a 3D movie, for example, it’s tricking your brain to see 3D by presenting two different images to each eye. Our display is not tricking your brain — we've used chemistry to structure light in three actual dimensions, so no tricks, just a real three-dimensional light structure. We call it a 3D digital light photoactivatable dye display, or 3D Light PAD for short, and it’s much more like what we see in real life,” said chemist Alexander Lippert. 3D Light PAD uses photoactivatable dyes that become reversibly fluorescent when illuminated with UV light. The photoactivatable molecules have a non-fluorescent “off” state, a fluorescent or visible absorbing “on” state that can be accessed by illuminating at a wavelength outside of the visible absorbance spectrum, a fast rate of photoactivation, and a fast deactivation to the “off” state. The 3D Light PAD can simultaneously activate and excite fluorophores in a spatial pattern defined by DLP, to generate a viewable and spatially accurate volumetric 3D image. The technology was developed at Southern Methodist University (SMU). Researchers tuned the photoswitch molecule’s rate of thermal fading by adding the chemical amine base triethylamine to it. “The chemical innovation was our discovery that by adding one drop of triethylamine, we could tune the rate of thermal fading so that it instantly goes from a pink solution to a clear solution,” Lippert said. “Without a base, the activation with UV light takes minutes to hours to fade back and turn off, which is a problem if you’re trying to make an image. We wanted the rate of reaction with UV light to be very fast, making it switch on. We also wanted the off-rate to be very fast so the image doesn’t bleed.” The researchers worked with a dye from the rhodamine class. For structuring light, a table-top display was used consisting of a commercial picoprojector, a UV projector and a custom quartz imaging chamber, 50 millimeters (mm) in size, to house the photoswitch and capture light. A liquid solvent was deployed inside the imaging chamber, as the matrix in which to dissolve the photoswitch dye (N-phenyl spirolactam rhodamine). Researchers projected patterns into the chamber to structure light in two dimensions using the off-the-shelf DLP projector for beaming visible light. For UV light, the researchers shined a series of UV light bars from the specially made 385-nm LED projector from the opposite side. Where the light intersected and mixed in the chamber, a pattern of 2D squares stacked across the chamber was displayed. Optimized filter sets eliminated blue background light and allowed only red light to pass. To get a static 3D image, the team patterned the light in both directions, with a triangle from the UV and a green triangle from the visible, yielding a pyramid at the intersection. One of the first animated 3D images the researchers created was the SMU mascot, Peruna, a racing mustang. The 3D Light PAD, patented in 2016, was fabricated for under $5,000. “For a really modest investment we’ve done something that can compete with more expensive $100,000 systems,” Lippert said. “We think we can optimize this and get it down to a couple thousand dollars or even lower.” SMU chemist Alex Lippert and his lab developed the 3D Light PAD. Courtesy of SMU. The researchers believe their discovery could be used in a variety of fields. Unlike 3D printing, volumetric 3D structured light is easily animated and altered to accommodate a change in design. Also, multiple people can simultaneously view various sides of a volumetric display, conceivably making amusement parks, advertising, 3D movies and 3D games more lifelike, visually compelling and entertaining. Volumetric 3D could also benefit the medical field. “With real 3D results of an MRI, radiologists could more readily recognize abnormalities such as cancer,” Lippert said. “I think it would have a significant impact on human health because an actual 3D image can deliver more information.” The current 3D Light PAD can generate more than 183,000 voxels. The researchers believe that scaling the volume size could increase the number of voxels into the millions. The researchers achieved of 200 microns for the display, which compares favorably to 100 microns for a standard TV display or 200 microns for a projector. The goal now is to move away from a liquid vat of solvent for the display to a solid cube table display. Optical polymer, for example, would weigh about the same as a TV set. The team is also considering use of an aerosol display. The researchers hope to expand from a monochrome red image to true color, based on mixing red, green and blue light. They are working to optimize the optics, graphics engine, lenses, projector technology and photoswitch molecules. “. . . Everything we see — all the color we see — arises from the interaction of light with matter,” Lippert said. “The molecules in an object are absorbing a wavelength of light and we see all the rest that’s reflected. So when we see blue, it’s because the object is absorbing all the red light. What’s more, it is actually photoswitch molecules in our eyes that start the process of translating different wavelengths of light into the conscious experience of color. That’s the fundamental chemistry and it builds our entire visual world.” The research was published in Nature Communications (doi:10.1038/ncomms15239). From watching Star Wars as a child, SMU chemist Alex Lippert brought to life his dream of crafting animated 3D shapes from light. Using photoswitch chemistry his lab constructed light shapes into structures that have volume and are viewable from 360 degrees, making them useful for biomedical imaging, teaching, engineering, TV, movies, video games and more. Courtesy of SMU.