If D is greater than zero, the medium has negative dispersion.
From the en.wikipedia.org
If D is less than zero, the medium is said to have positive dispersion.
From the en.wikipedia.org
If D is less than zero, the medium is said to have positive dispersion or normal dispersion.
From the en.wikipedia.org
Rosanov, N. N.Radiation reflection from inhomogeneities moving in a medium with a plasma dispersion law.
From the nature.com
A pair of prisms can be arranged to produce net negative dispersion, which can be used to balance the usually positive dispersion of the laser medium.
From the en.wikipedia.org
A reflection grating replicated onto a prism allows light to diffract inside the prism medium, which increases the dispersion by the ratio of refractive index of that medium to that of air.
From the en.wikipedia.org
In this case, the medium is said to have normal dispersion.
From the en.wikipedia.org
The Met Office issues air quality forecasts made using NAME, the Met Office's medium-to-long-range atmospheric dispersion model.