The total power spectrum of the n-th mode, i.e., the total power in the n = 0, 1, 2, 3 and 4 modes, normalized by the total power in the dipole (n = 1) mode. The results in (a) apply for the small-core NP, and the results in (b) apply for the large-core NP. The spectrum is shown for the concentric as well as eccentric cases; for the latter, the core displacements along the negative x-axis, x₁₂ = −1, 3, and 5 nm, are considered.