What is Holography?
brief answer…
Holography is three-dimensional laser photography. The hologram is a true, three-dimensional record of the original object. It contains depth and parallax, which is the ability to see around the object to objects placed behind.
followed by a more in-depth answer…
The word, hologram is composed of the Greek terms, “holos” for “whole view”; and gram, meaning “written”. A hologram is a three-dimensional record of the positive interference of laser light waves. A technical term for holography is wavefront reconstruction.
In holography, we record the positive interference of matching wavefronts of laser light. This three-dimensional record is formed as a diffraction pattern; a series of very fine lines, or concentric circles. This diffraction grating bends the viewing light back onto the path of the original recording wavefronts of laser light. The three-dimensional version of the object – the hologram – is reconstructed as light.
Types of Holograms
There are two basic types of holograms: transmission holograms and reflection holograms. Transmission holograms are clear film windows which transmit the viewing light. Reflection holograms are high contrast with dark backgrounds which reflect the viewing light.
Transmission holograms are usually recorded on film, which we laminate to Plexiglas. The resulting hologram is a clear window onto a holographic world which contains maximum depth, projection and parallax. However, the holographic imagery is only on a horizontal plane. Viewed vertically, or up and down, the holograms travel through a colorful rainbow smear, or spectral shift in color. Hence, transmission holograms are often called “Rainbow Holograms.” Rainbow holograms can contain shifting, overlapping colors and imagery of flowing motion of great beauty and interest.
Reflection holograms contain full parallax, with up to a foot of depth and projection on both horizontal and vertical planes. Reflection holograms’ sharp, high-contrasting imagery usually play back in a single color. Through photochemical techniques and double exposures, incredible colors can be obtained.
How are Holograms Made?
Our holograms are made on a large stable table with a laser, lenses, mirrors and other optics. The table is composed of a large mass resting on a vibration isolation system to dampen any movement. Since the hologram records light waves, movement as small as one-quarter of a wavelength of light will ruin the hologram.
To make a hologram, the laser beam is split into two beams. One part of the laser beam is directed by mirrors and spread by lenses to illuminate the object. The laser lights the object, then bounces off and hits the holographic film or plate positioned in front of the object. The other
portion of the laser beam, called the reference beam, is directed by mirrors and lenses to evenly illuminate the film. Where the two portions of the laser beam meet at the film, they interfere constructively and record the hologram.
This “constructive interference” of laser light’s waves is similar to the ocean’s waves traveling onto the beach. When two waves meet just right, their collision enlarges or amplifies their size. In holography, this wave amplification exposes the holographic film.
After exposure, the holographic film is developed, similar to black and white photography. After processing and drying, the hologram is ready for viewing. This series of steps results in a laser-viewable “Master” hologram.
White-light viewable holograms are created in a two step process. First, the laser-viewable Master is holographed. Then, a second hologram is made from the projected pseudoscopic image of the Master. This hologram can be reconstructed – viewed – in white light. The section on “Lighting Instructions” explains viewing a white-light hologram.
