The holography technology could record and display full information of three dimension objects by using interference and diffraction of light. It was invented in 1940s and develops to several types. For example, rainbow hologram is a wildly used technology on credit cards and currencies. Traditional hologram needs laser to reconstruct, but rainbow hologram only needs the white light, like sunshine. After this, people try to make hologram easier to reconstruct whereas the recording methods have not been simplified much. In the future, the digitalization may help holography go further.
Holography is a photographic technology which records all of the information ...view middle of the document...
One directly goes to photographic plate or other kinds of recording medium as the reference beam. The other very important light called illumination beam imprints the object to photographic plate as the reference beam does. After this, when these two light both reach the recording medium and interfere with each other, the phase and amplitude information of light wave on object has all converted into changes of intensity on space. Thus, all information is recorded by using the directions and spacing between fringe patterns .
Figure 1 Recording a Hologram 
Process of Display
The process of imaging procedures uses the principle of diffraction to recover the light wave information on object. The hologram acts as a diffraction grating in this situation. When this diffraction grating is illuminated by the exactly same reference beam, which includes the same orientation, shape, and wavelength, this 2D diffraction grating will diffract the beam and generates several diffraction waves. There are two images formed here; one is the original image, and another is the conjugate image. The reconstructed hologram is stereopsis because the hologram records all the light information on the object. Therefore, theoretically, the full image could reappear like the real one. In addition, one photographic plate could be exposure several times to record some different image and display them respectively without interfering .
Types of holography
There are several methods to make holograms. Transmission hologram belongs to one of the most basic hologram display. The principle of this uses coherent light on object, where The reflected and scattered light on surface of object form to new object wave when they reach the photographic plate, to record. Meanwhile, another reference light goes to the photographic plate at the same time. The hologram could be obtained by exposure of photographic plate. As for reconstruction, the same reference light is used to illuminate the photographic plate while eyes watch through the hologram in transmission light. The virtual image could be seen and is reconstructed as the real one. On the hand, if the conjugated reference light is used instead, a real image could be found on the other side of hologram . Transmission holograms display image clearly, and have large depth of field, but they are limit by length of coherent light wave. They also have to need laser to reconstruct. This causes speckle effect which means there is small and random distribution of graininess on surface of reproduced image.
The reflection holograms are invented to overcome the drawbacks of transmission hologram, which only can display by coherent light. Reflection holograms could use white light instead to reconstruct, for example the sun light. The object is on the top left of photographic plate which shows in the figure below. The point coherent light source illuminates from the other side of...