Archives of Holography Glossary

ARCHIVES OF HOLOGRAPHY GLOSSARY Glossary definitionswere provided l7y GrahamSaxl7y, 3 HonorAvenue, Goldthorn Park Wolverhampton, West Midlands WV45HF, UnitedKingdom. Thegreaterpart of thisglossary was originally published in GrahamSaxl7y, Practical Holography (UnitedKingdom: Prentice Hall) 1988. achromatic-(l) describes an optical system free from dispersion; (2) when used to describe a holographic image, colorless. additive color synthesis-a method of producing a multicolor image by mixing lights of different hues (see CIE chromaticity diagram ). alcove hologram-a concave cylindrical 180° holographic stereogram that projects a real image ofa computer-generated object to its center. The image may continue back from the center through the plane of the hologram to infinity. argon-ion (Ar+) laser-a gas laser using ionized argon gas as the lasing medium. Its most important lines in the visible spectrum are at 514.5 nm and 488 nm, beamsplitter-an optical device that divides a beam of light into two beams. Benton hologram-see rainbow hologram. birefringence-the property possessed by certain substances offorming two orthogonally polarized wavefronts from a single incident wavefront. Also known as 'double refraction'. black hole-a colloquial term for the threedimensional silhouette left when some part of the subject matter has moved during the exposure of a hologram. bleach-in holographic processing, a chemical solution that renders the photographic image transparent, changing an amplitude hologram into a phase hologram. Bleaches are described as 'rehalogenating' when they convert the photographic image from silver to silver halide; as 'reversal' when they remove the photographic image , leaving the undeveloped silver halide; and as 'total' when they remove both the developed silver and the undeveloped silver halide. Born approximation-s-a simplification of the mathematical description of the scattering of charged particles, which ignores the (very small) effect of the particles themselves on the scattering function. Bragg condition-the condition for efficient reflection of a light beam undergoing Bragg diffraction. In order to satisfy the condition, the optical path difference between wavefronts reflected from successive layers of material must be an integral multiple of the wavelength (see grating condition). Bragg diffraction-the principle by which a stack of parallel reflecting surfaces (or zones ofalternate high and low refractive index) will reflect a beam of light if and only if the reflected wavefronts are of appropriate wavelength and orientation to produce constructive interference. Bragg hologram-any hologram in which the Bragg condition is more important than the grating condition in forming the image. Brewster angle-the angle of incidence of a light beam on a surface such that the reflected and refracted beams are orthogonal , typically 56°_58°for glass. At the Brewster angle, the transmitted beam is partly polarized in the plane containing the incident ray and the normal to the surface (ppolarized ); the reflected beam is totally polarized at right angles to it (s-polarized). camera-in holographic terminology, a device for making holograms in which the sensitive material is totally enclosed in a lightproof container. Holographic cameras may be modified versions of photographic cameras or (more commonly) lightproof enclosures containing the entire optical system , including the subject matter. CIE chromaticity diagram-a diagram that gives a description of the color quality of a visual stimulus in terms ofhue and saturation . The color quality is defined in terms of coordinates specifying the equivalent content of red, green and blue stimuli that would give an exact visual match. CIE colorimetric system-a quasi-objective system for quantifying attributes of color such as hue, lightness and saturation, largely drawn from the CIE chromaticity diagram. coherence-the degree to which the photons in a light beam are in phase. It is usually defined in terms of temporal coherence , which is related inversely to the bandwidth, and of spatial coherence, which is related to the degree of correlation between the various parts of the beam. collimated beam (collimation)-(the production of) a beam of light that neither converges nor diverges. collimating lens/mirror-a lens/optical mirror that produces a collimated beam when light from a near-paraxial point source is incident on it. computer-generated hologram-originally a hologram drawn by a computer to produce a specific image or for spatial or correlation fil tering. The meaning is now generally extended to...