Interférences

Interférences, or interference, is the phenomenon that occurs when two or more waves overlap in space and time, producing a resultant wave whose amplitude depends on their relative phases. It is a consequence of the superposition principle and is observed across many wave types, including light, sound, radio waves, and quantum matter waves. Interference can be studied with coherent sources that maintain a stable phase relationship.

Constructive interference happens when waves arrive in phase, strengthening the signal; destructive interference occurs when they are out of phase, weakening or canceling it. The resulting pattern depends on wavelength, path difference, and coherence. Coherence length or time determines how far waves can travel before phase relations degrade.

Classic demonstrations include Young’s double-slit experiment for light, and various optical interferometers such as the Michelson, Mach-Zehnder, and Fabry-Pérot devices. Interferometry is used in precision metrology, spectroscopy, fiber optics, and astrophysical measurements. In gravitational-wave astronomy, laser interferometers like LIGO detect tiny changes in arm lengths caused by passing waves.

In engineering and communications, interference also describes unwanted overlap of signals, known as electromagnetic interference (EMI) or radio-frequency interference (RFI). Mitigation strategies include shielding, filtering, and careful spectral planning.

Quantum interference arises from the superposition of matter waves and underpins many quantum phenomena. Experiments with electrons, atoms, and molecules show interference patterns, illustrating wave-particle duality and guiding developments in quantum technologies.