Holograms are amazing pictures that appear to have depth just like the real object. For example, if you look at a hologram of the front of a cube and then move to one side, you will see the sides of the cube just as if you were walking around it. Holograms are made with lasers.
An ordinary photograph records the variations in light intensity reflected from an object. Holography, however, records not only the intensity of light but also its phase. In an ordinary photograph, we get two dimensional images but in holography we get three dimensional images.
Holography is the means of making three dimensional pictures called holograms. It was invented by Dennis Gabon, a Hungarian born physicist who worked in Britain in the year 1948. He was awarded Nobel Prize for Physics in 1971. But the actual holography became possible only after laser was developed at the beginning of the 1960. The intense-coherent light of laser allowed high quality holograms to be made.
To make a hologram, the object is lit by light from a laser. This light reflects from the object and strikes a photographic plate placed nearby. At the same time, the laser beam is split so that it also reflects from mirrors and strikes the plate directly.
The plate is then developed. A black and white pattern appears on it, producing a holographic plate. When one side of this plate is lit up by a laser beam and it is viewed from the other side, an image of the object appears behind the plate. The image is in three dimensions just like the real object, but in the colour of the laser light. Projection holograms can be projected by lasers to appear in front of the holographic plate. There are also special holograms that can be seen by day light.
Holograms have proved very useful. They are used to record very small changes in the size of the objects. This is because they can record an object from many angles with a great accuracy. Scientists use them to study the growth of crystals or the build-up of dirt on old oil paintings. They can be used in computer memory systems to store information. In the field of industries holography is being used to prevent the pirating of the goods of big companies. In India also, some big companies are using the holograms to distinguish their original goods from the copied ones.
