Diffraction of light is the bending of light waves as they pass around an obstacle or through an aperture. There are two main types of diffraction: Fraunhofer diffraction and Fresnel diffraction.
Understanding Diffraction
Diffraction occurs when a wave encounters an object or opening that has a size comparable to or smaller than its wavelength. Instead of traveling in a straight line, the wave bends around the obstacle or spreads out through the opening. This phenomenon is responsible for various optical effects, such as the colored fringes observed in soap bubbles or the spreading of light beams.
Types of Diffraction
There are two primary classifications of diffraction:
Fraunhofer Diffraction
- Description: Fraunhofer diffraction, also known as far-field diffraction, occurs when both the light source and the observation point are effectively at an infinite distance from the diffracting object. This is achieved experimentally by using lenses to collimate the incoming light and to focus the diffracted light onto a screen.
- Characteristics: Parallel rays of light are incident on the diffracting object, and parallel rays emerge from it. The wavefronts are essentially planar.
- Example: Diffraction patterns observed when light from a distant star passes through a small aperture.
Fresnel Diffraction
- Description: Fresnel diffraction, also known as near-field diffraction, occurs when either the light source or the observation point (or both) are at a finite distance from the diffracting object.
- Characteristics: The wavefronts are curved rather than planar. This type of diffraction is more complex to analyze than Fraunhofer diffraction.
- Example: The diffraction pattern observed when a light source is placed close to an opaque object.
Summary Table
| Feature | Fraunhofer Diffraction | Fresnel Diffraction |
|---|---|---|
| Distance | Source and screen at "infinite" distance. | Source or screen (or both) at finite distance. |
| Wavefronts | Planar wavefronts | Curved wavefronts |
| Experimental Setup | Lenses are used to collimate and focus the light. | No lenses required, simpler setup in some cases. |
| Complexity | Relatively simpler analysis. | More complex analysis. |
| Other Names | Far-field Diffraction | Near-field Diffraction |
In summary, diffraction is the bending of light waves around obstacles, and it is categorized into Fraunhofer diffraction (far-field) and Fresnel diffraction (near-field), based on the distances between the source, obstacle, and observation point.
