I had a strange dream last night.
Ken and I flew to Venezuela -- which was, in my dream, a sort of large tropical flea market. I found a display of holograms, and bought one that depicted a shoe. But when you turned the hologram to look at the shoe from different angles, it actually changed subtly, a very old work boot morphing into something modern as you rotated it. I decided, in my dream, that I was going to start collecting holograms. Then the dream got weirder, something about our bedroom being full of flies, but I woke up thinking about holograms.
Back in the early nineties you used to see decorative holograms for sale more often. I had one of a peace symbol that I wore as a necklace, and another one of space-walking astronauts, mounted on a little plastic stand, that sat on my dresser. These days it seems the novelty has kind of worn off, and you only see them on credit cards or as stickers on expensive products, verifying their authenticity.
Remembering my peace symbol and my astronauts, I thought maybe I really would start collecting holograms. I'm sure you can still order them off the internet, at least... Although that does take a bit of the fun out of collecting.
When I was in high school, some people I knew made their own holograms as an independent research project (they got a science credit for it.) I remember being impressed by little glass plates with 3-D coins on them, and by the laser they had set up in sandbox, on a concrete block that, according to the teacher, had its own foundation independent from the rest of the school, to minimize vibrations. These days I work in a laser lab, on, actually, the third floor of our building. The optical tables we use are supposed to be low vibration, if you use the built in hydraulic support system for the legs, but our tables are decades old and the hydraulics don't work anymore. I think my high school had a nicer set-up.
Our advisor has another lab, mostly separate from the one Ken and I work in, which is actually called the "holography" lab. But the holograms they make aren't like the ones I used to buy. They have more in common with DVDs, using a laser to store information and then retrieve it later. But they probably could make a picture of a coin, and I started thinking... Maybe I should ask them to show me how. I mean, will I get a chance again?
So that got me searching for "make your own hologram" kits. Turns out there are a few around these days. I don't have to bug the guys in the holography lab after all.
The only problem is, I think their holograms, like the ones you can make from these kits, would be viewable only in laser light of the same color as the laser used to create them. The kind of holograms I dreamed about collecting are embossed "rainbow transmission" holograms, apparently. All I really know about them is what I just read here. But they are certainly harder to produce, which is why they make good security stickers.
Also unfortunately, as far as I know you couldn't really make a hologram like the one I dreamed about, which morphs as you rotate it. Holograms are generally produced by shining a laser beam on a small object that is physically present. In the case of my astronaut hologram, it was almost certainly some plastic models of astronauts -- that's what they looked like. You can't combine images of different objects onto one hologram -- although you can record multiple holograms on the same piece of film, to be viewed with different colors of light.
So my dream can't exactly come true, even with a home hologram kit, or a whole holography lab.
There are other things holograms can't do. You can't make "true color" holograms that look like photographs except in 3-D, at least not in normal light. You may have seen something like this on a movie poster, but it's not a hologram. It's a "lenticular" poster. This is a completely different process that just makes different parts of a normal image visible from different angles. In general, the secret to making things look 3-D is to make each of your eyes see a slightly different image. But lenticular posters can hold a dozen different images, each visible from a different angle, so that not only can they look 3-D from different positions, they can even move or morph as you walk by. Any image you can print on paper can be used for this technique, physical models not required. So it's actually a more impressive and somewhat more useful technique than real holograms. But not as futuristic. Real holograms look three dimensional because they reproduce the light reflected off of actual three dimensional objects. Whereas lenticular images can show you only a dozen different angles on a scene, a hologram, like a real object, produces an infinite range of views.
What about holograms projected into empty space, like Princess Leia in Star Wars? Also not possible, unfortunately.
About the closest you can come is this arcade game, also from the early nineties. I played it. You really could reach in and put your hand "through" the characters.
But, as that Wikipedia link says, it was only an optical illusion, done with mirrors. Like the "mirage bowl", I guess. (My brother had one of those). The video game's images appeared only inside a sort of box, and couldn't be projected out into the room, the way R2-D2 projects Princess Leia.
More Star Wars-ish technology might be on the horizon, though. A Japanese company has a device that makes air glow in 3-D patterns. Again, not a hologram, but possibly much cooler. It seems to be sort of similar to the kind of "laser etching" used to create 3-D images in these crystals, only using the air itself as a medium. But the air will only keep glowing as long as they lasers are on, and apparently makes quite a lot of noise as it "explodes" from the heat, whereas once you burn a hole in the crystal, the hole stays.
I love this stuff. I can totally see myself accumulating a huge collection of cheesy 3-D toys and jewelry and posters. I'd also want to collect "Magic Eye" stereograms, including animated ones like the ones I linked to a while ago, and 3-D comics that you view with glasses, and probably Viewmaster slides -- I had one of those when I was a kid too.