where ω is the frequency, ω p is the plasma frequency in vacuum, γ is the damping coefficient, ε ∞ is the high-frequency permittivity, and ε 0 is vacuum permittivity. The background fluid has a real and constant permittivity ε f and permeability µ f over the frequency range of interest. Because the background ε f generally differs from ε 0 , it is convenient to use an effective plasma frequency, ω * p = ω p ε 0 /ε f , which simplifies many expressions. In all calculations other than Figure , γ/ω * p = 0.05 and ε ∞ /ε f = 1. Configurations are illuminated with linearly polarized incident light