Holography is a new type of photographic technology that records all the information in the reflected or transmitted light waves of the object being photographed. Ordinary photography utilizes the principle of lens imaging to record the surface image on the light-sensitive film reflecting the change in light intensity on the surface of the object being photographed.
Holography records the intensity of the reflected light waves of the subject, but also records the phase of the reflected light waves. This is achieved by superimposing a reference beam and a reflected beam from the subject on a photographic film to produce an interference pattern.
Holography is a kind of photographic record that expresses three-dimensionality through the cooperation of a set of auxiliary reference beams.
Light wave is a kind of electromagnetic wave, it carries the amplitude and phase information in the propagation. Ordinary photography uses a light-sensitive material (such as a photographic negative) as the recording medium, and a lens imaging system (such as a camera) to make an image of an object on the light-sensitive material. It is recorded only from the object of the intensity distribution of light wave image, that is, the amplitude of the information, but does not include the phase of the information. Therefore, ordinary photography can only take two-dimensional (flat) images. In order to simultaneously record the amplitude and phase information of light waves, with the help of a coherent reference light, the use of object light and the reference light of the optical range difference, in order to determine the phase difference between the two beams of light waves. Thus, with the aid of a reference light, information on the amplitude and phase of light waves from an object can be recorded.
Reference Baidu Encyclopedia Holography