Coherence (physics) - Examples of Wave-like States

Examples of Wave-like States

These states are unified by the fact that their behavior is described by a wave equation or some generalization thereof.

• Waves in a rope (up and down) or slinky (compression and expansion)
• Surface waves in a liquid
• Electric signals (fields) in transmission cables
• Sound
• Radio waves and Microwaves
• Light waves (optics)
• Electrons, atoms and any other object (such as a baseball, as described by quantum physics)

In most of these systems, one can measure the wave directly. Consequently, its correlation with another wave can simply be calculated. However, in optics one cannot measure the electric field directly as it oscillates much faster than any detector’s time resolution. Instead, we measure the intensity of the light. Most of the concepts involving coherence which will be introduced below were developed in the field of optics and then used in other fields. Therefore, many of the standard measurements of coherence are indirect measurements, even in fields where the wave can be measured directly.