Evanescent Wave

Definition

An evanescent wave is a type of wave that occurs when light or other electromagnetic radiation travels through a medium and encounters a boundary, leading to a decay of the wave's amplitude in the direction perpendicular to the boundary. This phenomenon occurs under conditions such as total internal reflection, where light is completely reflected at an interface rather than passing through it. The evanescent wave exists only in the region close to the boundary and diminishes exponentially with distance from the interface.

5 Must Know Facts For Your Next Test

1. Evanescent waves are created during total internal reflection and only extend a short distance into the second medium, typically on the order of a few wavelengths.
2. The amplitude of an evanescent wave decreases exponentially with distance from the boundary, meaning that it becomes weaker as you move away from the interface.
3. Evanescent waves play a crucial role in optical phenomena such as fiber optics and sensing technologies, allowing for efficient light transmission and detection.
4. These waves are not observable at great distances from the boundary, making them fundamentally different from traveling waves that propagate over long distances.
5. In quantum mechanics, evanescent waves can also be associated with tunneling phenomena, where particles appear to pass through potential barriers despite not having enough energy.

Review Questions

• How does total internal reflection lead to the formation of evanescent waves, and what implications does this have for light transmission?
  • Total internal reflection occurs when light hits a boundary at an angle greater than the critical angle, resulting in complete reflection rather than refraction into the second medium. This process generates evanescent waves that exist near the boundary and decrease in strength as they move away. The presence of these waves is essential for applications like fiber optics, as they enable light to travel along the fiber by continuously reflecting and creating an evanescent field that can interact with nearby materials.
• Explain the concept of critical angle in relation to evanescent waves and how it affects light behavior at boundaries.
  • The critical angle is defined as the angle of incidence beyond which total internal reflection occurs. For angles greater than this critical angle, instead of transmitting into the second medium, light reflects entirely at the boundary, resulting in the formation of evanescent waves. These waves exhibit unique properties, such as their exponential decay away from the boundary, which influences how light behaves at interfaces and is crucial for technologies that rely on total internal reflection.
• Analyze how evanescent waves contribute to advanced technologies such as optical sensors and fiber optics, discussing their underlying principles.
  • Evanescent waves are fundamental in technologies like optical sensors and fiber optics because they allow for efficient light manipulation and interaction with materials. In fiber optics, evanescent waves help maintain signal strength over long distances by facilitating continuous total internal reflection within the fiber core. In optical sensors, these waves can interact with changes in refractive index near the sensor's surface, enabling highly sensitive measurements. The ability of evanescent waves to couple with external environments enhances performance and sensitivity in various applications.

Related terms

Total Internal Reflection: The complete reflection of a wave, such as light, when it hits a boundary at an angle greater than the critical angle, preventing any transmission into the second medium.

Critical Angle: The minimum angle of incidence at which total internal reflection occurs, specific to the pair of media involved.

Refraction: The bending of waves when they pass from one medium to another due to a change in speed, which can lead to phenomena like total internal reflection.