In holography, the light scattered from an object is recorded and presented in a way that appears to be three-dimensional. This is a photographic method that enables a wavefront to be recorded and later reconstructed. A hologram is a three-dimensional image formed by the interference of light beams from a laser or other coherent light sources. A hologram is constructed by superimposing a second wavefront on the wavefront of interest, resulting in an interference pattern that is recorded on a physical medium. There are different types of holograms created over the years. Transmission holograms and rainbow holograms are two important holograms used for crucial purposes. The transmission holograms enable light to shine through them and the image to be viewed from the side. The rainbow holograms are used for security purposes (on credit cards, driving licences, etc.). Holograms can also be generated using computers by modelling two wavefronts and combining them together digitally. The resulting digital image is then printed onto a suitable mask or film and illuminated by a suitable source to reconstruct the wavefront of interest.
Working of Hologram:
The main factors required to create a hologram are a laser, a recording medium, a person or object to record, and favourable conditions to carry out the entire process. First of all, the laser is turned on and the laser beam is split into two identical beams. These two beams are then redirected using a mirror. The two beams formed are called the illumination beam and the reference beam respectively. The illumination beam is directed at the object and the reference beam is directed onto the recording medium. The two beams intersect and interfere with each other. The interference pattern is then stamped on the recording medium to recreate a virtual image for our eyes to see. This is the basic working process of a hologram. The most important part used for this process, the recording medium, where the lights converge is composed of various materials. Photographic film with an added amount of light-reactive grains is one of the most common things used for hologram creation. These types of photographic films helps the resolution of the two beams to be higher and as a result, the resulting image looks more realistic.
History of Holography:
The history of holography started way back in the late 1940s when Dennis Gabor, a Hungarian-British physicist started to develop the technology of holography. Dennis Gabor utilised the findings of other scientists including Mieczyslaw Wolfke, a Polish physicist in 1920 and William Lawrence Bragg, a British physicist in 1939 to enhance more developments in the field of x-ray microscopy. Yes, actually the discovery of holography was an unexpected one as Dennis Gabor was doing research to improve electron microscopes and he ultimately reached to holography. At that time, the discovery was known as electron holography. The optical holography was not that developed during those days and it finally started to develop with the discovery of laser in 1960. The holography that we see today started it’s revolution in 1962 when Yuri Denisyuk (a Russian physicist) Emmett Leith and Juris Upatnieks (American physicists) developed laser technology that recorded 3D objects in the University of Michigan, US. During that time, silver halide emulsions were used in the recording medium. But, the clarity of the resulting image was not perfect. The problems slowly started to fade as a result of technological advancements. Many new methods evolved including the conversion of transmission with the refrective index and all these methods helped the field of holography to be better and better as days passed.
Applications of Holography:
Some of the important applications of holography are listed below.
- The 3D images produced by holograms are used in various fields including technical, educational and advertising fields.
- Hologram can be used for the process of data storage. It is proved that even a small broken piece of hologram contains full data and information about the object with a reduced clarity.
- Holography is used to detect stress in materials. A stressed material will deform, sometimes so minutely that it is not visible. This change can be amplified by a hologram as the light reflected off the material will now be at a different angle than it was initially.
- Holography finds a crucial application in fighter aircrafts. The fighter pilots use holographic displays of their instruments so that they can keep looking straight up.
- In museums, holograms are used to keep archival records.
- Holography is used for biomedical applications especially in Europe and the US. Holograms are constructed inside live organs via optical fibers giving more details than any previous alternate techniques.
- Hologram can be used to directly observe the instantaneous growth rate of a live plant. The rigid body movements can be isolated from the net growth information using optical fibers.
- Holographic scanners are employed in store check-out counters for reading the bar codes. A rotating computer generated hologram performs the scanning process and detects the scattered light.
- Holography is used in a new type of computer called “optical computer.” An optical computer is a device that uses visible light or infrared beams, rather than electric current to perform digital computations.
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Check your knowledge
Answer. A hologram is a three-dimensional image formed by the interference of light beams from a laser or other coherent light sources.
Answer. Illumination beam and reference beam.
Answer. A. The 3D images produced by holograms are used in various fields including technical, educational and advertising fields.
Hologram can be used for the process of data storage. It is proved that even a small broken piece of hologram contains full data and information about the object with a reduced clarity.