Researchers in Japan have created a floating 3D holographic plasma display... with haptic feedback. The system, which is being presented at SIGGRAPH 2015 next month, can render up to 200,000 voxels per second, but the physical size of the display is just 1 cubic centimetre.

The system works by way of using a femtosecond laser to turn small pockets of air (voxels) into plasma. A femtosecond laser is a laser that fires for an incredibly short period of time—on the order of one quadrillionth of a second (or one millionth of one billionth of a second, if you prefer). The laser hits an atom or molecule, causing an electron to become ionised (move to a higher energy level). Shortly after, the electron loses its extra energy in the form of a photon that is emitted as visible light.

To go from a single plasma dot to a 3D display, the researchers passed the laser through a spatial light modulator (SLM) connected to a PC to create the hologram, and then a galvano scanner and varifocal lens to "draw" each voxel with specific X, Y, and Z coordinates.

One of the more intriguing aspects of the 3D display is that it also incorporates haptic feedback. According to the research paper, when you touch one of the voxels, "shock waves are generated by plasma ... the user feels an impulse on the finger as if the light has physical substance." The researchers don't go into any further detail on the topic, however.







The paper (freely available on arXiv) also notes that using a femtosecond laser (as opposed to a picosecond or nanosecond laser) is one of the more novel aspects of the system. Because the laser bursts are so short, the plasma isn't that energetic, and so it's safe to touch. The researchers also tested a nanosecond laser, but found that it burned a piece of leather within 100 milliseconds. The femtosecond laser setup appears to be safe and doesn't cause any skin damage when a user touches the display, though you still shouldn't look into the laser source.

For now, the holographic plasma display is too small to be of much use—and perhaps more importantly, the equipment used to produce the display is too large and expensive for anything outside of the lab. The principles are all quite sound, though, and there's a lot of interest in free-space display technologies that don't require some kind of screen or other medium to project the image onto.

ACM SIGGRAPH 2015. DOI: arXiv:1506.06668 (About DOIs).