Figure 8

Dependence of the number \(N_{\min }\) of local minima of the objective function \(R(\cdot )\) found within an interval of \((d_1,d_2) \in [10,1]\, \upmu \hbox {m} \times [10,1]\, \upmu \hbox {m}\) on the absorption coefficient \(\kappa _1 \equiv {\text {Im}}(n_1)\) of the inner layer (\(s=1\)) of a two-layered cylinder. For each ratio \(\frac{d_1}{d_2}\) of layer diameters (left: \(\frac{d_1}{d_2} = 0.2\), centre: \(\frac{d_1}{d_2} = 0.6\), right: \(\frac{d_1}{d_2} = 0.9\)), a number of different values of \(\kappa _1\) was considered. It turns out that the layer diameter ratio generally determines the behaviour of \(N_{\min }\), as can be seen from the fact that \(N_{\min }\) attains similar values for different outer layer diameters \(d_2\). Lines are guides to the eyes only.