Figure 2

Measured power spectrum |z(ω)|² as a function of angular frequency ω.

The measurement is made with a plasmonic resonant cavity with a periodic array of gold disks of diameter d = 300 nm. The cavity separation is r = 1 μm and the intensity modulation frequency is ω′ = 56.51 kHz (f ′ = 9 kHz). The solid line is a fit to Eq. (2) with m = 3.46 × 10⁻⁸ g, ω₀ = 43.79 kHz and ξ = 4.64 × 10⁻⁸ Ns/m.