Critical polarization suppression in the near-field interference of moving Huygens-like dipoles

Motion underpins various exotic phenomena in nature, such as the Doppler effect, and enables numerous practical applications. In this study, we reveal a counterintuitive phenomenon that p-polarized surface plasmons cannot be excited for all directions and Doppler frequencies, when a complex dipolar source moves parallel and close to the planar interface that supports the propagation of surface plasmons under a newfound critical suppression condition. The underlying mechanism is that the motion provides an extra degree of freedom to reshape the near-field interference of dipolar sources themselves and could be exploited to fully suppress p-polarized waves carried by the judiciously designed dipolar source at all Doppler frequencies. To be specific, this critical polarization suppression arises when the dipolar source acts as a moving Huygens dipole, with its electric and magnetic dipole moments being in-phase and mutually perpendicular. Moreover, this Huygens-like dipole must move with a critical velocity, which is determined solely by the ratio of the source’s electric to magnetic dipole moment, but irrelevant to surface plasmons' phase velocity.