HOLOGRAPHY

In this lecture, we are going to learn about the holography system, how holography works, the construction of holograms, the principle of holography, and its applications of it. So let’s start with a unique topic which can be the future.

Introduction of Holography

• In conventional photography when an object is photographed by a camera, it records only the intensity distribution and hence produces a two-dimensional image of a three-dimensional object.

• A new technique known as holography was developed by Gabor in 1947. The Greek term ‘holos’ means whole and ‘graphics’ means writing. Therefore, holography means a complete recording.

• Thus, holography is a technique of recording the amplitude and phase of the light waves reflected from an object. Hence, a three-dimensional image of the object can be obtained. The recorded photograph is called a hologram.

Principle of Holography

The principle of holography can be explained in two steps:

1. Recording of hologram or construction of hologram. The recording of the hologram is based on the interference of coherent light waves.
2. Reconstruction of the hologram. This reconstruction of the hologram is based on the diffraction of light waves.

Recording or Construction of Hologram

• The process of making a hologram is referred to as the recording of a hologram or construction of a hologram. This is based on the principle of interference of light.

• The light from a laser source is split into two components S and R, as shown in Figure below:

• One of the beams, Splitter Beam (S), is directed towards the object while the other beam Reference beam (R) is directed towards the photographic plate. The wave illuminating the object is called the object wave or signal wave, and the wave directed towards the photographic plate is called the reference wave.

• Since both waves S and R are derived from a single source, they behave as coherent beams. Thus, the two beams interfere with each other producing an interference patterns on the photographic plate. Hence, the record of this interference pattern constitutes a hologram.

• The developed hologram will look like an ordinary negative. But it contains a complete record of the original object, recorded in the form of an interference fringe pattern.

Reconstruction of Hologram

• Reconstruction of a hologram refers to the method of retrieving the original image from a hologram. This is based on the principle of diffraction of lightwave waves.

• The below figure shows the method of reproducing the real and virtual image of the object.

• The developed hologram is exposed to a laser beam of the same wavelength, which was used while constructing the hologram. This laser beam called the readout wave or reconstruction wave interacts with the interference pattern on the hologram and gets diffracted to produce two images of the original object.

• On looking from the far side of the hologram, an observer can see the virtual image occupying the same position as the original object. This virtual image V₁ is indistinguishable from the object and appears in three-dimensional form. One can observe the different perspectives of the object on moving his eye.

• The other image called the real image, R_I is formed between the observer and the hologram. The real image will appear inverted in-depth. This image is also known as the pseudoscopic image which can be recorded.

Applications of Holography

1. It is used in data storing systems.
2. It is used in producing a 3D image of an object.
3. It is used in studying the distribution of strain in an object subjected to stress.
4. It is used in scanners.
5. It is used in displaying a 3D image.

Frequently Asked Questions on Holography

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