ABSTRACT
To the physicist, a hologram is a record of the interaction of two mutually coherent light beams, in the form of a microscopic pattern of interference fringes. To the well-informed lay person, it is a photographic film or plate that has been exposed to laser light and processed so that when illuminated appropriately it produces a three-dimensional image. To the less well informed it is just some kind of three-dimensional photograph. Certainly, both photography and holography make use of photographic film or plates, but that’s about all they have in common. The image is produced in a totally different way: you can’t even describe the way the two types of image are formed in the same terms. You can show how a camera lens produces an optical image using a simple ray diagram and basic geometry; but to explain a holographic image you have to invoke the concepts of diffraction and interference, and these are wave phenomena.
