What is meant by diffraction? State its types and differentiate them.

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written 8.3 years ago by

teamques10 ★ 69k

The bending of light around the sharp edges of opaque obstacles or apertures is defined as diffraction.
The phenomenon of diffraction depends on the size a of the obstacle and the wavelength λ of the light wave as illustrated in figure below:

If the size of the obstacle compared to the wavelength of the light wave is:
- Very small (i.e. a<<λ), then the wave will undergo reflection and not diffraction.
- Very large (i.e. a>>λ), then the wave will not be diffracted.
- Almost equal (i.e. a ≈ λ), then the wave will undergo maximum diffraction.

Types of Diffraction:

Fraunhoffer diffraction. In Frensel's diffraction the source and screen are finite distance to obstacle, but in this case the source of light and screen placed infinite distance from obstacle. In this case parallel rays and plane wavefronts are produced because of using lens.
Fresnel diffraction. It means that source of light and screen at finite distance from the obstacle. In this case no lenses are used for making rays parallel. The wavefront is either spherical or cylindrical.

Difference

Fraunhoffer	Fresnel
1. Source and the screen are far away from each other.	1. Source and screen are not far away from each other.
2. Incident wave fronts on the diffracting obstacle are plane.	2. Incident wave fronts are spherical.
3. Diffracting obstacle give rise to wave fronts which are also plane.	3. Wave fronts leaving the obstacles are also spherical.
4. Plane diffracting wave fronts are converged by means of a convex lens to produce diffraction.	4. Convex lens is not needed to converge the spherical wave fronts.

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