New Media Dictionary: Part IV: Holography

The New Media Dictionary project [1] was born out of the desire to name and define the many and varied forms of art that have developed in conjunction with technology. A whole lexicon is being created to describe the many processes, techniques, instruments, and critical and aesthetic concepts--in short, the entire emerging culture--of this immense laboratory workshop.

The terms selected for this issue come from the field of holography. The terms and definitions have been chosen by the Groupe de recherche en arts médiatiques (GRAM).

(Some of the more general terms concerning holography have appeared in a previous installment of this project in Leonardo Vol. 33, No. 2 [2000].)

Interested artists and researchers are invited to submit additions and comments to Section Editor Louise Poissant [2]. These contributions will be added to the electronic version of the dictionary, with credit to the author. In this way, the New Media Dictionary will gradually become a collective project, in which each significant contribution will find its place.

These definitions were prepared by Georges Dyens and Philippe Boissonet. Project director: Louise Poissant. Translator: Lou Nelson.

Dictionary Terms--Part IV: Holography

Aberration--The deformation of a holographic image, usually caused by an alteration in the optical setup. Examples include chromatic aberration, spherical aberration, field curvature and curvilinear distortion.

Achromatic Hologram--A white-light reflection or transmission hologram in which the dominant shades are black and white. Unlike photography, which in its early days produced only black-and-white images, holography produces color images by its very nature. In optics, this term is used to refer to the lenses that correct chromatic aberrations.

The first achromatic hologram was created in 1975 by Stephen Benton, Will Walter and Herbert S. Minges, in the United States. The black-and-white effect of these holograms was achieved by controlling the colors such that the image was recreated by additive color synthesis (red, green, blue).

Acoustical Hologram--A hologram formed by the interference of two high-frequency sound beams.

Alcove Hologram--A transmission or reflection hologram on a transparent, concave, semi-cylindrical surface, with a viewing angle of nearly 180°.

The alcove hologram was developed by Stephen Benton at the Massachusetts Institute of Technology Media Lab. It is one of the more recently conceived types of computer-generated holograms viewable with white light.

Beam Path--The path taken by the laser object beam and reference beams to the point of contact with the holographic recording material. The two beam paths must be of equal length when recording a hologram.

Beam Splitter--A partially reflecting mirror or holographic optical element used to split a laser beam into two beams of varying intensities. One beam is direct, the other reflected. There are also variable beam splitters, which are usually circular and have a graduated reflecting surface so that the operator can set the desired intensity ratio.

Benton Hologram--See white-light transmission hologram.

Bichromated Gelatin--See dichromated gelatin.

Bleaching--A chemical process used during the final stage of development of a hologram to improve the brightness of the image, increase the diffraction effect and make it transparent. Bleaching is important when working with reflection holograms, which otherwise have very little natural brightness, but is optional when working with transmission holograms. The chemical composition of the substance used in bleaching varies according to the developer or fixer used, as well as the type of holograms being bleached.

Brewster Angle--In holography, the angle obtained using incident light such that the refracted and reflected beams are perpendicular to each other. A Brewster angle can only be achieved on a transparent medium; the reflected beam is polarized. The Brewster angle is at 55° to the recording plate, which makes it possible to obtain minimum refraction and maximum reflection.

Coherence--The behavior of a group of waves that have the same frequency and that propagate uniformly in phase.

Coherence Field--The volume of space within which an image can be recorded. The extent of the recordable volume depends...