Page 27 - Studio International - February 1970

Technology
Margaret Benyon in collaboration with
Peter Spicer of B.A.C.
Interference Pattern Box 1969
Hologram, reconstructed by laser
fessor Gabor in 1947, but full implementation
was not possible till the development of the
laser, which is a source of light all of whose
and art waves are 'coherent', or in step. Benyon uses a
red helium-neon gas laser. (Holographic tech-
niques now exist which do not require lasers,
but so far their capture of contrast and detail
HOLOGRAPHY AND INTERFERENCE tends to be inferior.)
Holograms by Margaret Benyon of Notting- To make a hologram, a laser beam is usually
ham University are to be shown at the Lisson split into two beams by a semi-transparent
Gallery, London, during February. They can mirror. One beam, the 'signal beam', is
be considered both as finished artifacts, de- aimed at an object, and light waves are
veloping naturally from Miss Benyon's stereo- reflected from it, so that a pattern of wave-
scopic paintings (which are also on view), and fronts flows from the object to a photographic
also as an embryonic stage in the growth of plate. Another beam, the 'reference beam', is
holographic art, a medium which may well aimed straight at the plate, where it interacts
prove eventually as significant as photography with the signal beam. Thus the photographic
has been. plate records interference patterns, the wave-
Laser holography was first achieved by Leith fronts of the two beams either augmenting
and Upatnieks in 1963, but still has no major each other to leave a bright spot on the plate,
industrial applications. A recent survey by an or cancelling out to leave a dark spot. This
American investment research firm predicts kind of interference does not happen with
that the las& market as a whole will grow ordinary light, because the light waves are
slower than is generally expected until 1974, unrelated to each other in phase and interfere
when it will grow faster than is now antici- chaotically, with no patterning effect. Ordi-
pated. Holography (together with hole-drill- nary photography can record only light
ing) will be one of the two major applications intensity, but a holographic plate— apparently
of lasers, and they forecast that by 1975 it will a haphazard jumble, when viewed in ordinary
receive acceptance by industry for stress light—records information about the wave-
analysis and non-destructive testing. Longer- fronts themselves : their phase and amplitude,
term potential applications include the photo- in fact everything that the eye would intercept
graphy of high-speed events; information if it were located at the position of the plate.
processing and storage; chemical, seismo- The 'code' can be broken when the hologram
graphic and weather analysis; and 3-D is illuminated with another laser beam. The
movies, television and x-rays. effect of holography is to 'freeze' an inter-
The details of holography, both theoretical ference pattern until one chooses to recon-
and practical, are difficult and I am not struct it; and another name for the technique
qualified to discuss them; but the broad is `wavefront reconstruction'.
principles are straightforward enough. The Some special properties of the hologram are
original concepts were introduced by Pro- as follows :
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