Fig. 3: Near-field scattering of dipolar sources and their spectral dependence.

The measured (top) and calculated (bottom) BFP intensities of s- and p-polarised near-field angular distributions for a λ = 520 nm, b λ = 640 nm, and c λ = 700 nm that correspond to various relative contributions of electric and magnetic dipoles and their relative phases. The sets of s- and p-polarised intensity distributions are normalised to their common maximum value. For λ = 640 nm, the Janus condition (\(\left| {p_x/m_y} \right| = 0.75/c\) and ΔΦ = arg(m_y/p_x)=π/2) is theoretically satisfied. The s-polarised component of the light that is scattered by the Janus dipole presents a full ring of zero intensity at the locations \(k_x^2 + k_y^2 = k_t^2 = k_0^2\left( {R^2 + 1} \right),\) which correspond to the noncoupling condition for the specified amplitude of the wavevector k_t in any direction. In (a) and (c), the dipole moments and the phase difference that are used in the theoretical plots are the same as the experimental values, while in (b) the simulation shows the ideal Janus dipole, with \(\left| {p_x/m_y} \right| = 0.75/c\) and ΔΦ = π/2