Diffraction

Diffraction is a phenomenon that occurs when a wave encounters an obstacle or a slit. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Similar effects occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, X-rays, and radio waves.

Introduction

While diffraction always occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves whose wavelength is roughly similar to the size of the diffracting object or slit. If the obstructing object provides multiple, closely spaced openings, a complex pattern of varying intensity can result. This is due to the addition, or interference, of different parts of a wave that traveled to the observer by different paths, where different path lengths result in different phases.

Types of Diffraction

There are two types of diffraction: Fraunhofer diffraction and Fresnel diffraction. Fraunhofer diffraction or far-field diffraction is a form of wave diffraction that occurs when field waves are passed through an aperture or slit and observed at a distance from the obstacle. On the other hand, Fresnel diffraction or near-field diffraction is a process that occurs when a wave passes through an aperture or goes around an object and the size of the aperture/object is comparable to the wavelength of the wave.

Applications

Diffraction has practical applications in many areas of science and engineering. For example, it is fundamental to the understanding of light and color, and it is also essential in the field of acoustics and sound technology. In addition, it is used in the field of x-ray crystallography to study the structure of crystals.

See Also

• Wave
• Light
• Sound
• X-ray crystallography

References

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