Fig. 4.

Example of the convergence of the boundaries as a function of the iterations: (a) the optical index of the core ( $n_1\hspace{0.17em}=\hspace{0.17em}\sqrt{{\varepsilon }_1}$) (b) the radius of the core, (c) the thickness of the shell, (d) the absorption efficiency. The minimum and the maximum for each parameter for the last iteration are the final results. The plot of the convergence of the wavelength is useless since its interval remains almost the same at each iteration.