The phenomenon whereby the → refractive index
of light in a medium changes rapidly with wavelength in the vicinity of
an → absorption band.
Hence the → dispersion curve
of the substance shows marked deviations from
→ Cauchy’s equation, in contrast with the behavior of
→ normal dispersion.
On the shorter λ side of the absorption band the refractive
index falls off more rapidly than required by Cauchy’s equation representing
values of n for visible light. On the long λ side of the absorption band
the index is very high, decreasing at first rapidly and then more slowly as one goes beyond
the absorption band.
See also: → anomalous; → dispersion.
