Focusing surface plasmon polariton wave packets in space and time

The spatiotemporal focusing of surface plasmon polariton (SPP) wave packets (WPs) by planar plasmonic-lens coupling structures is described using combined femtosecond interferometric time-resolved photoemission electron microscopy (ITR-PEEM) imaging and model simulations. The focusing properties of lens structures inscribed lithographically into Ag films depend on the angle of incidence of the excitation field. Severe aberrations are introduced by the phase delay in the interaction of obliquely incident plane waves with the commonly employed circular arc-shaped lens structures. It is shown that the aberration can be corrected by accounting for propagation delays caused by the incidence angle-dependent retardation of the optical field-lens structure interaction. The focusing of SPP-WPs in both space and time is demonstrated with aberration corrected lens structures.