Question

Describe diffraction with the help of an example.

Answer 1

Diffraction is a term that describes a variety of phenomena that arise when a wave comes into contact with an obstacle or an opening. It's known as the bending of waves around the corners of an obstacle or through an aperture into the area of the obstacle's geometrical shadow.

Complete answer:
We shall understand diffraction with the help of the example, which is a laser beam's propagation.Diffraction is the process of determining how the beam structure of a laser beam varies as it propagates. It approximates a Gaussian beam structure and has the lowest divergence for a given diameter because the whole emitted beam has a planar, spatially coherent wavefront. The smaller the output beam, the faster it diverges.

By first extending a laser beam with one convex lens and after collimating it with another convex lens whose focal point is coincident with the first lens, the divergence of the laser beam can be reduced. As a result, the resultant beam has a greater diameter and, as a result, has a smaller divergence.

If the propagation medium's refractive index increases with the light intensity, the divergence of a laser beam can be decreased below that of a Gaussian beam or even reversed to convergence. This may trigger a self-focusing effect.The laser beam divergence will be smaller in the vertical direction than in the horizontal if the vertical transverse coherence length is greater than the horizontal.

Note: Diffraction varies depending on the wavelength of light. Shorter wavelengths are diffracted at a larger angle than longer wavelengths (in effect, violet and blue light are diffracted at a greater angle as compared to red light).