Evanescent wave

Definition

An evanescent wave is a near-field optical phenomenon that occurs when a wave travels along a boundary between two different media, resulting in an exponentially decaying amplitude away from the interface. This type of wave is crucial in various applications, particularly in sensing technologies where it interacts with surface plasmon resonance to enhance signal sensitivity.

5 Must Know Facts For Your Next Test

1. Evanescent waves are generated when light undergoes total internal reflection at a boundary, creating a field that extends into the lower refractive index medium.
2. The decay length of an evanescent wave is typically on the order of a few hundred nanometers, which makes them highly sensitive to changes in their environment, such as molecular binding events.
3. In surface plasmon resonance applications, evanescent waves are utilized to probe the surface of metal films, allowing for real-time monitoring of biomolecular interactions.
4. The intensity of an evanescent wave decreases exponentially with distance from the interface, meaning that only very close objects can effectively interact with these waves.
5. Evanescent waves play a vital role in many sensing technologies, including biosensors and optical devices that exploit their ability to enhance signal detection near surfaces.

Review Questions

• How do evanescent waves contribute to the principles of surface plasmon resonance in sensing applications?
  • Evanescent waves contribute to surface plasmon resonance by generating a strong electromagnetic field at the interface between metal and dielectric layers. This field enhances the sensitivity of sensors as it allows for the detection of minute changes in refractive index caused by biomolecular interactions occurring very close to the surface. The ability of evanescent waves to penetrate just a short distance into the dielectric medium makes them ideal for probing these interactions without interference from bulk solutions.
• Discuss the relationship between total internal reflection and the generation of evanescent waves, emphasizing the importance of angle and refractive indices.
  • Total internal reflection occurs when light traveling from a medium with a higher refractive index to one with a lower refractive index strikes the boundary at an angle greater than the critical angle. This causes the light not to pass through but instead reflect entirely back into the first medium. During this process, an evanescent wave is created at the interface, extending into the second medium with an exponentially decreasing amplitude. This relationship is critical for applications that utilize evanescent waves, as controlling angles and refractive indices allows for precise manipulation and measurement capabilities.
• Evaluate how evanescent waves can be harnessed in nanotechnology and biosensing applications to improve detection methods.
  • Evanescent waves can be harnessed in nanotechnology and biosensing by utilizing their unique properties to detect interactions at surfaces with high sensitivity and specificity. For instance, in biosensing applications, the interaction between target molecules and surface-bound probes can be monitored through changes in the intensity or phase of the evanescent field. This enables real-time detection of biological events at low concentrations, which traditional methods may miss. Additionally, advancements in nanostructured materials can enhance these effects further, allowing for more effective diagnostics and environmental monitoring through tailored sensing platforms.

Related terms

Surface Plasmon Resonance: A resonant oscillation of conduction electrons at the interface between a negative and positive permittivity material that can be excited by light, allowing for sensitive detection of molecular interactions.

Total Internal Reflection: A phenomenon that occurs when a wave hits a boundary at an angle greater than the critical angle, causing it to reflect entirely back into the medium, leading to the formation of evanescent waves at the interface.

Localized Surface Plasmons: Collective oscillations of conduction electrons in metallic nanoparticles that can interact with incident light, enhancing local electromagnetic fields and facilitating various nanotechnology applications.