Eidispersiiviset

Eidispersiiviset is a Finnish term used in specialized discussions of wave propagation and materials science to describe systems, media, or phenomena that do not exhibit dispersion. The word is formed from ei- meaning “not,” dispersiivinen meaning “dispersive,” and the suffix -iset, which makes a plural adjective. It designates cases where the phase or group velocity of waves does not depend on frequency over the considered range.

In practice, eidispersiiviset describe idealized or approximate situations in which the refractive index remains effectively constant with respect to wavelength, or where pulse shapes are preserved during propagation. The concept appears in introductory explanations of non-dispersive media and as a simplifying assumption in models across optics, acoustics, and signal processing. Real materials typically show some dispersion due to electronic, vibrational, or structural resonances, so eidispersiiviset regimes are usually limited to specific spectral bands or to theoretical constructs.

Usage notes: the term is not widely standardized in international literature and may be most common in Finnish-language sources, where it is contrasted with dispersiiviset phenomena. When translated, the closest English equivalents are “non-dispersive” or “dispersion-free.” In many contexts, its practical relevance lies in justifying the neglect of wavelength-dependent refractive index in simplified models.

See also: dispersion, non-dispersive media, refractive index, phase velocity, group velocity.

References: standard optics and wave-propagation textbooks; Finnish-language technical sources on optics and acoustics in which the term may appear.