There are various methods to produce that kind of imagery.
The japanese also managed to create 3d images in ''mid-air'' though these use lasers to create ''dots'' in the air.
In a certain way it's better because it's more independant (whereas those other devices depend on the air not moving, due to disturbance in the
image.)
I also remember a videoclip of a holographic projection of Kate Moss, but I forgot how that one was achieved.