Evolutia, let us separate your question into its component parts: Physics (laser holography) and Illusion (part of existentialism).
Physics: Laser holography has been around since the 1950's. Basically, we take four lasers aimed into the center of a radiative medium (a partial vacuum doped with 2/He\3 works well). The reason to use helium-3 is that it illuminates at such a low energy. Air also radiates, but it takes far more energy and the image must move at high speed to keep from "flashing."
Next, using 4 to 6 beam splitters, controlled by a computer (and software that is no longer on the market), aim one color each of laser light into each of the beam splitters, so that the beams intersect. That gives you an illusion of a "pixy" (not quite a "pixel") which would represent one point on the outside of the intended illusion. Keep the power to a minimum, as past about 4-5 miliwatts, shorter-wavelength laser will cause the air to fluoresce along the length of the beam. You want the intersection to show 8-10 mw, which will cause the air to fluoresce.
Note that the lasers need not operate in the visible spectrum. However, the vectorial sum of the two wavelengths must fall in the visible spectrum for the hologram to be visible. Note that most lasers operate in the IR and UV spectrum in security systems applications: there is no way for an intruder to detect these beams. http://en.wikipedia.org/wiki/holography
http://en.wikipedia.org/wiki/laser
As to the second part of your question: existentialism. Why don't I save you some time and send you a link? http://en.wikipedia.org/wiki/existentialism.
