The way that holograms work is described here. Holograms work by recording the patterns of light and interference patterns on holographic film or plates. You see light is a wave (and a particle but that part isn’t relevant here.) As with any wave, light has crests and troughs. The crest is the top of the wave and the trough, the bottom. When two waves meet, one of a few things happen:
- The crests and troughs coincide. When this happens the amplitude (”height”) of the wave doubles. This is called constructive interference (sounds like an oxymoron, doesn’t it?)
- The two waves are completely out of sync. This causes the crests and troughs to overlap. If the two waves had the same amplitude, they will cancel each other out completely. This is destructive interference.
- The last possibility is when the waves aren’t in perfect sync, or perfectly inverse. When this happens you get a unique pattern of interference.
You might be asking, “OK Michael, so you can combine light waves. How does that make holograms?” When you make a hologram, you are actually recording those patterns of interference. The principle is that if you take two waves and put them together, you get a unique third wave. By subtracting one of the first two waves from the third you can re-create the other original wave. So by shining light on the hologram, you get one of the patterns of light waves back. Because the light you shine on the hologram is constant (not in a pattern) it looks the most like the reference beam (the one that shines directly on the film). This causes the other light waves to be re-constructed, giving you the object beam. And the object beam is a “copy” of the light reflected off the original object.
Because the light picked up by each eye is a little different, and because the interference pattern is different for every light beam that hits the hologram, it comes out differently. Because the eyes pick up slightly different versions of the image, the brain is fooled into seeing a 3D image. So in reality this is basically an optical illusion.
History | How They Work | Links | Main Hologram Page | Multibeam Holograms | Setup | Singlebeam Holograms
