mikejuk writes with this story about a Japanese team working on creating touchable holograms. I Programmer reports: "One method of creating a volumetric, i.e. true 3D, display, is to use a high power laser and focus it on a small spot in space. The air in that spot will be heated to the point where it ionizes and glows with a bright blue light. Scan the laser really fast and you can make a full 3D arrangement of glowing points of light — not exactly a hologram but as good as. Of course, the big problem is that you have a lot of energy being focused on small areas and human interaction could be a problem. You might well get burned by the laser if you attempted to touch or interact with the display. The solution is to use a really fast laser, a femtosecond laser, that heats a small spot to a high temperature but only for a very short time. This is much safer because the total energy involved is smaller. This is the reason you can touch sparks without getting burned."