How can a hologram reconstruct a view of an object?

A hologram can show a view that changes as a viewer moves, even when the original object is absent. The important difference from an ordinary photograph is how light is recorded and later redirected. A hologram is not simply two flat pictures shown to two eyes.

During recording, light scattered by an object meets a reference beam at a sensitive surface. The two light fields interfere: their overlapping wave patterns create fine variations in intensity. With coherent illumination, whose wave relationship stays stable enough during recording, those variations can be preserved as a fringe pattern.

The reference beam gives the pattern information about how the object light’s wave timing varies across the surface. During reconstruction, suitable light illuminates the recorded pattern. The pattern diffracts that light, redirecting it into several components. One can reproduce the object light’s wavefront, the shape and timing of the arriving wave across space.

Light can then enter the viewer’s eyes along paths consistent with an object at the recorded location. The object itself need not be there. Recording geometry, illumination, wavelength and the available viewing region matter. An arbitrary stripe pattern does not automatically reconstruct an object, and not every hologram works under the same lighting conditions.