How does diffraction make it possible for a hologram to reconstruct an image?

In holography, diffraction is the fundamental mechanism that allows a hologram to reconstruct a three-dimensional image of an object. During the recording process, light reflected from an object interferes with a reference beam to create a complex pattern of interference fringes on a photographic plate. These fringes act as a diffraction grating.12

When the developed hologram is later illuminated by a coherent laser beam, the fine-detailed fringes diffract the light, bending it to reverse the original conditions of the coherent waves that created the hologram. Essentially, each point on the original object contributes to the formation of a zone lens pattern on the hologram; when light passes through these patterns, it is diffracted to recreate the original optical field. This process produces both a virtual image and a real image, effectively reconstructing the phase and amplitude information of the original object, which provides the depth and three-dimensional characteristics of the scene.12