Spherical micro and nano particles with different refractive indices under plane wave illumination have been studied by using the 3D multiple multipole (MMP) method. The intensity distribution that emerges in the vicinity of the particle’s rear boundary (with respect to its plane wave illumination) has resulted in a tightly focused photonic nanojet [1, 2]. The resulting beam waist significantly undergoes the diffraction limit, where the nanojet emission extends over several optical wavelengths without suffering from significant diffraction providing a pencil-like area of high optical intensity. In our contribution, we report on the optimization of both the dielectric material and the particle shapes (oblate ellipsoids) in order to maximize the power confinement in the nanojet. Different 3D-MMP models are applied and discussed. 0246050100150200 Fig.1: Nanojet emission from an oblate dielectric ellipsoidal particle (n=2) illuminated by a plane wave from the left (λ = 500 nm; E-polarization): a) The time-averaged Poynting field modeled with 3D ring multipoles b) The Radiation pattern (intensity distribution in the “focal plane” against the lateral extent given in µm) showing a beam waist of WFWHM=120 nm for the particle’s major and minor axis of Rx=5 µm and Ry=2.5 µm.