To make a holographic image, you need to capture the way an object scatters light, then try to recreate that effect in three dimensions. From LiveScience:
A laser beam is split into two identical beams and redirected by the use of mirrors. One of the split beams, the illumination beam or object beam, is directed at the object. Some of the light is reflected off the object onto the recording medium.The second beam, known as the reference beam, is directed onto the recording medium. This way, it doesn't conflict with any imagery that comes from the object beam, and coordinates with it to create a more precise image in the hologram location.The two beams intersect and interfere with each other. The interference pattern is what is imprinted on the recording medium to recreate a virtual image for our eyes to see.
Chances are pretty good that we'll get Star Wars-esque 3D effects from augmented reality glasses before we get stand-alone projections that can produce the illusion of lifelike depth. But as Nye explains, the latter is certainly possible.
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