1947: Holography - The book of science

Holography
Full spectrum
Half a hologram
Commentary

Holography

Dennis Gabor created the hologram
to correct the spherical abberation
of the electron microscope.
A photograph records the frequencies
and intensities of normal light
scattered in one direction from a scene.
A hologram records the interference pattern
of coherent light reflected from a scene
in multiple directions so that diffraction
of the original light source can recreate
a field of light reflected in the same direction
as light from the original scene.

Full spectrum

The first holograms were monochromatic.
Dennis Gabor used a mercury lamp through a pinhole
to record holograms one centimeter in diameter.
Today, holograms can be made in full color
using red, yellow, and cyan lasers,
or by increasing the depth of the recording media
and relying on Bragg defraction to select colors.
Rainbow holograms are visible under normal light
but sacrifice vertical or horizontal parallax.
Pulsed lasers and phase congugation
permit recording and reconstruction of moving holograms.
Holograms can also be generated by computer
so as not to require any light in their making.
Holographs can be used for general data storage
and for measuring surface irregularities, vibrations,
swiftly moving objects, and fluid flows.

Half a hologram

Half a hologram
records all the image
but with more noise.
Dennis Gabor said
the human memory
could be holographic.
Lose half of it
due to age or illness
and the memories are still there
with less clarity,
less confidence,
less speed of recall.

A holograph relies on the wave nature of light. It captures the interference pattern, where half of a split laser beam reflects off a scene and the other half, called the reference beam, bypasses the scene to interfere with the reflected light. To reconstruct the light from the scene, illuminate the hologram with a beam that is identical to the reference beam.