Alright, it seems as though the scientific explanations are getting more thumbs down, than thumbs up. The multicolor, grainy, raster image of the holograms in Star Wars suggest some kind of projection trick like a couple of the arcade games of the early eighties that used concave mirrors and curved Fresnel lenses to produce hologram-ish 3-D effects. The true hologram is more like a kind of negative exposed on a super fine-grained black and white photographic plate. To produce, it requires a coherent laser light, and a beam splitter. If I remember correctly, half the beam has to go through the photographic plate from front to back, close to where the observers eye would be, and the other half has to go around behind the plate, and bounce off the object to reflect onto the backside of the plate. Since the plate is clear glass (or plastic) the light coming from both sides meets in the surface of the the emulsion, and that's where the wave fronts show up on the film. Where the wave fronts add up, that makes a dark spot on the negative, where they cancel out, they don't expose the plate and a clear area is left. Of course all of this happens on a microscopic scale, but it looks like a repeating Jackson Pollock under a powerful microscope. TRY THIS at home: Shine a red laser pointer through a silkscreen, or any very fine synthetic even-weave fabric. you should see a square-grid cluster of laser dots on the wall. That's not because the laser light is shining through the holes the way a pen-light would shine through a wicker chair, rather the spacing of the pattern is independent of how far away the laser is from the screen. If you use an old VGA screen from a smashed monitor, you'll get a hexagonal grid. I think we'll see something more like the holodeck in Star Trek (light only, no touch for a while) by tiling flatscreens with holographic capabilities on the walls of a room. Now, about those holographic capabilities, the real trick to 3-D is to make a slightly different image for every tiny arcsecond of angle of observation. Your two eyes see two slightly different versions of the image and your brain puts it back together again. You need to produce some kind of interference wave front, maybe a laser diode behind every pixel, with something like a little ultra-high resolution LCD screen in fron of every laser pixel. (Try 25nm black pixels) Or maybe you could just produce a phased array of visible light slot antennas, with light squirting out of the slits. Making a holographic figure stand out in the the open without some kind of screen behind it is a different matter. Maybe within a room, you could project an interference pattern on the walls and furniture.
TRY THIS: using a green laser pointer, in a darkened room, strap down the "ON button" with a zip-tie (temporarily) and aim it up at the ceiling, and put it in a coffee cup so that it holds still. Now observe the speckled light that shines back down into the room. It's better observed on a sheet of typing paper or white posterboard. I think what you're seeing is the raw interference of the different wave fronts caused by all the different levels of the particles of paint in the ceiling. If you move the posterboard toward and away from the spot projected on the ceiling, you'll notice that the pattern doesn't change, it only gets larger the farther you move away. This interference pattern is similar to the speckles on the holographic plate. Even an LCD or LED-backed flatscreen produces some rainbow repeating patterns around the reflection of a lightbulb. In order to get the free-floating hologram like princess Lea, the best route might be a swarm of luminescent nanobots like a cloud of lightning bugs.
PICTURE #1:(aluminum foil rough, dull side)