Femtosecond laser excited two-photon photoemission electron microscopy facilitates the studies on optical properties and dynamics of surface plasmon polariton (SPP) wave packets beyond the diffraction limit. In this article we review our recent work on imaging of SPP wave packets excited by an obliquely incident 10 fs laser pulse at a single slit fabricated in a thin silver film. We image the forward propagating polarization beat that is formed by the interference of the excitation laser light and the SPP wave packet fields. By systematically varying the slit width from sub- to multiple-wavelength scale, we observe modulated increase of the beat intensity, which is phenomenologically accounted for by the enhanced light-SPP coupling efficiency. By using a time-resolved pump-probe technique, we also show the temporal evolution of SPP wave packet that is imaged as the delay-time dependent displacements in space of the beat pattern.