Figure 4.

(a) Band diagram of Au around the L point, showing absorption from d to s bands only for ω > ω_IB, intraband scattering (s–s) and inelastic light scattering (ILS). (b) Origin of anti-Stokes scattering background produced by ILS from the thermally excited electrons above the Fermi level (shaded red). Plasmonically coupled light excites these electrons to a virtual state where they relax down to empty states just below the Fermi energy, emitting blue-shifted (anti-Stokes) light. (c) Measured background intensity at ν = ± 0 cm^–1 from fits to Stokes and anti-Stokes data at each temperature.