holography in laser
Holography is a technique to record and reconstruct a three-dimensional scene on a two-dimensional plane (hologram) based on optical diffraction and interference.
There are three types of holograms:
Reflection hologram.
Transmission hologram.
Hybrid hologram.
The photographic recording of the image is called a hologram, which appears to be an unrecognizable pattern of stripes and whorls but which—when illuminated by coherent light, as by a laser beam—organizes the light into a three-dimensional representation of the original object.
Today, different laser wavelengths are used to create holograms. The holography can be in different wavelengths lasers . Originally, HeNe lasers with a wavelength of 633 nm or various wavelengths from Argon/Krypton ion lasers were used as light source.
The holography can be in regular lights. However if a Laser source is used instead, then the three emerging beams will be in different directions. This is called ‘Off-Line Holography’. Holography in laser allows us to observe one kind of beam at a time. This is the reason that a laser is needed in holography.
To record display holograms one of the beam serves as a reference beam where the other beam illuminates a three-dimensional object. Both beams are then combined forming a pattern in a photosensitive medium. To record the hologram the holographic pattern has to be illuminated, usually also with a laser source.
A moving object can be made to appear to be at rest when a hologram is produced with the extremely rapid and high-intensity flash of a pulsed ruby laser. The duration of such a pulse can be less than 1/10,000,000 of a second; and, as long as the object does not move more than 1/10 of a wavelength of light during this short time interval, a usable hologram can be obtained. A continuous-wave laser produces a much less intense beam, requiring long exposures; thus it is not suitable when even the slightest motion is present.