## dispersion (for spectroscopic instruments)

https://doi.org/10.1351/goldbook.D01793
$$\text{Dispersion of a material}=\frac{\text{d}n}{\text{d}\lambda }$$ where $$n$$ = @[email protected] and $$\lambda$$ @[email protected]; $$\text{angular dispersion}=\frac{\text{d}\mathit{\varPhi }}{\text{d}\lambda }$$ where $$\mathit{\Phi}$$ = @[email protected]; and $$\text{linear dispersion}=\frac{\text{d}x}{\text{d}\lambda }$$ where $$x$$ = separation of spectral lines. The reciprocal of the last-named quantity is more frequently used ($$\frac{\text{d}\lambda }{\text{d}x}$$), and is commonly expressed in $$\unicode{x212B}\ \text{mm}^{-1}$$.
Source:
Orange Book, 2nd ed., p. 101 [Terms] [Book]