Detecting electromagnetic radiation scattered from
a tip−sample junction has enabled overcoming the diffraction limit
and started the flourishing field of polariton nanoimaging.
However, most techniques only resolve amplitude and relative
phase of the scattered radiation. Here, we utilize field-resolved
detection of ultrashort scattered pulses to map the dynamics of
surface polaritons in both space and time. Plasmon polaritons in
graphene serve as an ideal model system for the study,
demonstrating how propagating modes can be visualized and
modeled in the time domain by a straightforward mathematical
equation and normalization method. This novel approach enables
a direct assessment of the polaritons’ group and phase velocities, as
well as the damping. Additionally, it is particularly powerful in
combination with a pump−probe scheme to trace subcycle changes in the polariton propagation upon photoexcitation. Our method
readily applies to other quantum materials, providing a versatile tool to study ultrafast nonequilibrium spatiotemporal dynamics of
polaritons.