The concept of an "evanescent field" is related to wave phenomena, specifically to the behavior of waves at the interface between two different media, such as the boundary between two materials. However, it is important to note that the term "evanescent field" is not typically associated with a single photon, as a photon is a quantum of electromagnetic radiation.
When a wave encounters an interface between two media, such as a boundary between two transparent materials, a portion of the wave can be transmitted into the second medium, while another portion is reflected back into the first medium. In addition to transmission and reflection, there is another phenomenon that occurs at the interface: the wave can also penetrate slightly into the second medium, but its intensity decays exponentially with distance away from the interface. This decaying field is known as the evanescent field.
The evanescent field carries energy and information, but its intensity diminishes rapidly as it moves away from the interface. It does not propagate like a regular wave, but instead, it exists only in the vicinity of the interface. The evanescent field can interact with objects close to the interface, allowing for various applications such as evanescent wave sensing, near-field microscopy, or waveguides that guide light in integrated optical circuits.
In the context of a single photon, which is a quantum particle, the notion of an evanescent field is not commonly used. Quantum mechanics describes the behavior of photons through wave-particle duality, where a photon can exhibit both particle-like and wave-like properties. However, the concept of an evanescent field, as a classical wave phenomenon, is not directly applicable to the behavior of a single photon.