- Introduction to the Instrument
Holography enables high-density storage, encryption, and three-dimensional display of objects. Unlike conventional photography, holography does not record a two-dimensional image of a three-dimensional object on film, but rather the light field itself. Conventional photography records only the variations in light intensity on the surface of the subject—that is, it records only the amplitude of the light—while holography records the complete information of the light wave, including both amplitude and phase. In other words, all information regarding the light wave field of a three-dimensional object is stored in the recording medium.
Holography involves two processes: recording and reproduction. A coherent light beam is split into two beams: one illuminates the object to be recorded, and the light waves scattered from the object are called the object beam; the other beam, at a specific angle to the object beam, directly illuminates the holographic dry plate and is called the reference beam. The object beam and the reference beam undergo coherent superposition, producing fine interference fringes similar to those of a diffraction grating. These fringes are recorded on the holographic plate, forming a holographic negative, known as the holographic recording. When the hologram is illuminated with the original reference light, the diffracted light waves reproduce the wavefront of the object beam at the time of recording, thereby recreating a three-dimensional image identical to the original object.