The complex Fresnel equations allow a powerful method of materials analysis known as ellipsometry. In general, linearly polarized light reflected at an oblique angle will become elliptically polarized, with linear and circular polarization components that depend on the real and imaginary parts of χ. Measuring the reflectivity of both components of polarization therefore gives the real and imaginary parts of χ.

Plot the reflectivity spectrum for s-polarized light for an ensemble of N identical, isolated damped oscillators in a medium, as a function of frequency for several angles of incidence. (The s and p polarizations are defined in Section 3.8.1.) Pick ω₀ = 1, Γ = 0.1, and e²N/mV = 1.