The word hologram comes from Greek, with holos meaning whole and graphe meaning writing. A hologram is an advanced form of photography that allows an image to be recorded in three dimensions, in fact a recording of an interference pattern made by the interaction of two beams of light.
A company in Dresden, Germany, called SeeReal, developed a prototype holographic screen that generates a three-dimensional holographic video that only you can see. The prototype is 50 centimeters across, the largest holographic video display ever built and it's based on an eye-tracking technology.
The working principle of the hologram is not that complicated. Light coming from a laser is split into two beams, called the object beam and the reference beam. Spread by lenses and bounced off a mirror, the object beam hits the object. Light waves reflect from the object towards a photographic film. The reference beam heads straight to the film without hitting the object. The two sets of waves meet and create a new wave pattern that hits the film and exposes it.
On the film all you can see is a mass of dark and light swirls, it doesn't look like an object at all! But shine the laser reference beam through the film once more and the pattern of swirls bends the light to re-create the original reflection waves from the object, exactly.
The new applications greatly simplify the usually complicated calculations required to make a screen diffract light to produce a moving hologram viewable from any angle, so that an ordinary computer can do the calculations by using twin webcams to track the viewer's eye movements.
So the result is totally based on what you look at on the screen, and can make monsters in an online game, for instance, jump out of the screen and float in the air before you, creating a three-dimensional holographic video that only you can see.
