1. Diffraction and light propagation

The principle of holography is based on the phenomena of interference, diffraction and light propagation. It involves a recording phase and a reconstruction phase. A coherent light wave illuminates an object or group of objects. The wave reflected or transmitted by these objects is superimposed on a reference wave, and the interference pattern produced by this superposition, the hologram, is recorded. The term "in-line holography" is used when the illumination beam and the reference beam are one and the same.