What is a Hologram?

This chapter first discusses Denis Gabor's invention of holography, and addresses a number of categories of 3D imaging which are regularly referred to as holograms. It also discusses some of the important milestones in the development of hologram. The hologram differs greatly from the simple photographic recording of an image based solely on the amplitude of light arriving from the field of view of the optical system, because when people look at a black and white film exposed in an everyday camera, after applying developer, they see a perfectly recognisable “negative” image of the subject beyond the lens. In comparison, in its simplest form, the hologram recording itself, in the appropriate high‐resolution silver halide film or plate, tends to be something that, at first sight, is a meaningless jumble of lines or zones in varying tones. The conditions for recording a hologram involve the use of a coherent light source.