Figure 3.6 — Polarisability Figure 3.6 — Polarisability. Real (black solid line) and imaginary (dashed line) part of the polarisability with radiative correction [Eq. (3.25)] plotted as a function of (a) the particle radius a and (b) the size parameter k0a for a particle of relative dielectric permittivity εp = 2.25 (typical for glass in the optical spectrum) illuminated by an electromagnetic field with vacuum wavelength λ0 = 633 nm. The grey solid line represents the Clausius–Mossotti polarisability [Eq. (3.15)].