Why Don't We Have Princess Leia Holograms Yet?

It's one of the most iconic scenes in all of science fiction: In the original Star Wars, the droid R2-D2 projects a 3-D image onto a tabletop. Princess Leia, projected as a tiny hologram, desperately asks the semi-retired Jedi master Ben Kenobi for assistance: "Help me, Obi-Wan Kenobi. Still brings the chills, doesn't it? The free-standing 3-D hologram has been a staple of science fiction for decades. But like the phaser and the flying car, it's one of those sci-fi dreams that has yet to become reality. We're getting awfully close, though. Earlier this summer, researchers at the University of Rochester unveiled the latest projection system to approximate Princess Leia's immortal plea. Dubbed the Illumyn 3-D Display, the system uses laser projection to generate actual 3-D holograms in midair -- no projection surface, no virtual reality goggles, no 3-D glasses, no augmented reality tricks. There is a catch, however: Holograms projected by the Illumyn system are contained within a glass sphere filled with heated Cesium vapor, an elemental metal that's particularly good at emitting light. The Illumyn system works by crossing two laser beams -- invisible to the human eye -- at a specific point within the sphere. When the crossed beams hit the cesium vapor, various atomic-scale shenanigans produce a sky-blue light that is emitted outward in all directions. The crossed beams only produce a single point of light, but by moving the laser coordinates around at incredible speed, the Illumyn sphere can essentially draw 3-D objects in thin air -- well, thin cesium vapors. The image never actually exists at any one time, but the system fires up each dot so fast that the human eye sees the programmed image. The process is actually a kind of high-tech update on the old cathode-ray tube television, says Curtis Broadbent, research associate in the Department of Physics and Astronomy at the University of Rochester and co-developer of the Illumyn system. "CRT televisions used a raster-scan technology," Broadbent says. "The electron gun sends a stream of electrons to the fluorescent screen and the beam of electrons are deflected to sequentially hit every pixel on the fluorescent screen.