You have probably seen holograms on stickers, in stores, and maybe even galleries, such as at the MIT Museum. A hologram is a three dimensional image recorded on a piece of film.
When I was your age, I had my own holography studio. With my lab partner Todd, I built a sandbox holography table underneath the staircase in the science building at Loomis Chaffee where we would expose the holograms. We used a set of lenses, lasers, and film from Metrologic. You can still buy the kit! Then we used an abandoned dark room next door to develop the holograms. Making a hologram is similar to the traditional method for making photographs. You expose the film to light reflected from an object, and then you develop the film.
There are some subtle differences. With a photograph, you are recording a projected image on the film. The film is highly sensitive, but low resolution. Holographic film is superhigh resolution and not as sensitive, because the silver-halide grains on the film are much smaller. But what is recorded on the film is NOT an image of the object. To produce a hologram, you need two beams of light to create an interference pattern. One beam comes from light reflected from the object, and the other is a reference beam. This interference pattern is recorded on the piece of film. As the details of the interference pattern are extremely small the film needs to be high resolution. And the light needed for the exposure has to be single wavelength, as that produced by a laser. Exposing the film is difficult as the “camera” and the object need to be stationary the entire exposure time, which could last several seconds. You are used to seeing blurry images in photography. With a hologram, your interference pattern cannot move one fringe or nodal line.
After the film has been exposed to the pattern, it is developed, and you have made a very complex and special diffraction grating. When you shine light through this special diffraction grating, the light bends, or spreads in such a way that it reproduces an image of the original object in three dimensions! In the discussion of diffraction I mention that a diffraction pattern was related to the image of an object using the Fourier Transform. So a hologram is a recording of this Fourier Transform of the image of an object with three dimensions of information.
You can learn more the same way I did at the beginning by reading through the Metrologic guide. After high school I produced some advanced holograms in college and attended several training seminars and symposium. When I taught in Philadelphia I used to make holograms with all of my students.
