Fraunhofer vs. Fresnel Diffraction: Key Differences Explained

Let’s explore the fascinating phenomenon of diffraction, which occurs when a wave encounters an obstacle. Imagine waves bending around corners – that’s diffraction in action! In this scenario, the obstacle essentially becomes a secondary source, propagating the wave in new directions. When we’re talking about light waves, this bending of light around the edges of an obstacle is specifically called “diffraction.” To put it simply, it’s the encroachment of light into what should be the geometrical shadow of an object.

Figure: Diffraction of light waves

There are two primary types of diffraction: Fraunhofer and Fresnel. Let’s break down each one.

What is Fraunhofer Diffraction?

In Fraunhofer diffraction, both the light source and the screen are considered to be at an infinite distance from the obstacle causing the diffraction. This means we’re dealing with plane wavefronts approaching the object, effectively as if the object were at infinity. The resulting diffraction pattern is observed in a specific direction and appears as a fringed image of the light source itself.

What is Fresnel Diffraction?

Fresnel diffraction, on the other hand, occurs when the light source and the screen are at a finite distance from the obstacle. This happens when light originates from a point source and encounters an object in its path. The waves involved are spherical (or cylindrical), and the diffraction pattern you see is a fringed image of the object itself, not the source.

Fraunhofer vs. Fresnel: Key Differences Summarized

Here’s a table outlining the key differences between Fraunhofer and Fresnel diffraction: