Holography

[johnfp]

What is a Hologram?

A hologram is a 3-Dimensional picture of an object. You need a laser and special holographic film to make a hologram. You also need at least 2 laser beams from the same laser at the same time (to interfere). The easiest hologram to make is a Single Beam Reflection hologram. Although the name “Single Beam” sounds like you are using only one beam, you are not. You are still using two. Let me explain.

A laser is expanded by a lens and shined on a holographic plate (film) lying against an object. Remember I said you needed two laser beams from the same laser to make a hologram? Well, there are two beams that hit the holographic plate. One beam is the beam that comes directly from the laser to the holographic plate. A lot of this light goes through the plate because holographic plates are pretty clear. The laser light the goes through this plate bounces off the object and is reflected back to the holographic plate. This is the second beam. These two beams interfere to create and interference pattern on the holographic plate. After the plate is developed you shine a light on the plate and you see the hologram. The hologram looks exactly like the object you used to make the hologram. You can even turn the plate side to side to see the sides of the object. It is truly 3 dimensional. When you make a hologram the two beams cannot move relative to one another by even as much as ¼ of a micron. A human hair is about 90 microns across. Leaning the plate right on the object helps to make sure nothing moves during the exposure.

There are more elaborate set ups that use beam splitters to split the laser beam and mirrors to steer the laser beams to different parts of the object giving more natural lighting. These set ups have to be on a special table that holds all the beam splitters and mirrors stable so they do not move ¼ of a micron.