Reflection and Refraction Maxwell's equations lead to definition for ...

DispersionThe angular dispersion D Aof the grating can be obtained bydifferentiating the grating formula with respect to wavelengthFor constant incidence anglemλ = d( sin α + sin β) Grating FormulaD A = dβdλ ===md cosβd(sin α + sinβ)dλ cosβsin α + sinβλ cosβsin α fixedFor nearly normal incidence, α is small so β is small, and so cosβdoes not change much with λ- D Adoes not change much with wavelength- much better dispersion element than prismCEM 835 page 3-15