Hologram and Holography - Materials And Techniques

There are many sorts of holograms, classified by their differences in material (amplitude, thick/thin, absorption),diffraction (phase), orientation of recording (rainbow, transmission and reflection, image plane, Fresnel, Fraunhofer), and optical systems (Fourier and lensless Fourier). The hologram is usually defined as a record of an interference pattern in a chemical medium, but the pattern does not have to be produced by a light source, nor must the hologram be stored on photographic film. Sonic, x ray, and microwaves are used as well, and computers can generate ones just by using mathematical formulas.

Researchers have been experimenting with aspects of the holographic process all along, and new tests are always being devised, in order to explore novel ways to improve the resolution and vibrancy of the images. The most common differences among these methods involve the mechanical setup of the exposure, the chemistry of the recording medium, and the means of displaying the final product. Full color holograms can be made by creating three masters in red, green and blue, after painting the object in grayscale tones, according to a separation technique already used in art printing. Different shades of gray are interpreted by a combination of the masters as different colors. Fiber optic delivery systems can insure proper illumination and eliminate aberrations which arise during long exposures. Multiplex or multiple-exposure holograms can be in planar or cylindrical form, showing a 360-degree view or even apparent movement.