Everytime, we see Holograms on various products for identification purpose. Holograms are fascinating as they change with light.

Lets study how these are made.

Holograms are simply layered variations of an image. Each variation reflects according to light falling onto it. Holograms are nothing but 3 dimensional photograph and are produced by interface of two laser beams. Here, laser beam is simply referred to as light. In the lab, where it is produced, color of light varies according to its wavelength. Apparatus used to produce holograms have shutter which either allows light to pass through or blocks it. In such apparatus, light beam is splitted in two parts, each separating other at 90 degrees angle. There is one big screen in the apparatus, on which, interference of both lights are clearly visible. This screen has defined fringes onto it.

Most important factor in producing Holograms is stability of light. A slight tap on the table may produce a quality hologram and at the same time, can even spoil it completely as these lights are very sensitive to vibrations. Image that needs to be used to produce a hologram, can be anything. For example, a sculpture made of modelling clay and this sculpture's image needs to be produced as a hologram. This sculpture is positioned with the supporting rod that has magnetic base and kept on the metallic table. Then glass is kept in front of the object. Here, object is nothing but the sculpture, made of clay. For this experiment, table needs to be perfectly stable with no imbalances. Beam separator separates the beam, one at the behind of the object and the other in the front of the object.

With the help of A4 size paper, one part of beam is headed towards the sculpture. Beam first passes through the object lens which diffuses the light then it is reflected back by the parabolic mirror, which prevents it from loosing its intensity. As this can be said as part of photography, film is required.  so, in this, holographic film is attached to the glass plate. After attaching it, another piece of glass is placed so that film doesn't moves. Vibration of one tenth of wavelength is tolerable. Clips are then used to keep both the glass intact so that holographic film doesn't move. After placing clips, the laser is turned ON. Intensity of it reaches to 250 mWatts. Normal exposure time of object towards beam is about 1 second. But for some holograms, object is exposed to the laser just for 12 nanoseconds, very short period of time. Once, this is done, film needs to be developed as done in photography in dark room. There are several trays which contains different chemical solutions.

First, film is soaked into developer for two minutes. This solution blackens it. Then this blackened film is then soaked into the solution called as Bleach. This solution eliminates the parts which blackened it. Now, the film is rinsed. Rinsing of film is necessary to remove all acids in the emulsion so that it doesn't gets contaminated when it is then immersed. At this stage, film becomes transparent. Again, it is then rinsed in clear water. It is then kept into wetting agent for about one minute which eliminates all water spots. This allows film to become dry and finally, image of scultpure is produced on it. Producing of holograms can be done in one hour and in the maximum time of 5 hours , depending on the complexity of the projects. Some holograms are also produced by animation by using multiple still images. In this way, Holograms are prepared.

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