Emodes

Emodes is a term that appears in several technical contexts, generally signifying a defined set of states, patterns, or modes associated with electromagnetic or polarization phenomena. Because there is no single, universal definition, the precise meaning of emodes depends on the discipline and the source.

In cosmology, the term often appears as E-modes, describing a class of polarization patterns in the cosmic microwave background. E-mode polarization patterns are curl-free and are produced primarily by density (scalar) perturbations in the early universe. They can be distinguished from B-mode patterns, which contain curl-like structures that may arise from gravitational waves or gravitational lensing. The designation E-mode derives from a mathematical decomposition of polarization fields into electric-like (E) and magnetic-like (B) components.

In engineering and applied physics, emodes may be used informally to refer to electromagnetic modes of a system such as a resonator, waveguide, or optical fiber. These modes are solutions to Maxwell’s equations that describe how the electromagnetic field propagates within a given geometry. Common categories include transverse electric (TE), transverse magnetic (TM), and, in some contexts, transverse electromagnetic (TEM) modes. In these uses, emodes is not a formal standard term, and writers typically specify the geometry and mode type explicitly.

See also E-mode polarization, B-mode, polarization, waveguide mode, optical mode.