Basic Principle of Holography:
Holography is based on the principle of interference. A hologram captures the interference pattern between two or more beams of coherent light (i.e. laser light).
One beam is shone directly on the recording medium and acts as a reference to the light scattered from the illuminated scene
The hologram captures light as it interests the whole area of the film, hence being described as a ‘window with memory’. By contrast a photograph captures a single small area ‘aperture’ of perspective, the photographic image being created by focusing this light onto film or a digital sensor.