  We introduce ultrafast low-energy electron diffraction (ULEED) in
backscattering for the study of structural dynamics at surfaces. Using a
tip-based source of ultrashort electron pulses, we investigate the
optically-driven transition between charge-density wave phases at the surface
of 1T-TaS2. The large transfer width of the instrument allows us to employ
spot-profile analysis, resolving the phase-ordering kinetics in the nascent
incommensurate charge-density wave phase. We observe a coarsening that follows
a power-law scaling of the correlation length, driven by the annihilation of
dislocation-type topological defects of the charge-ordered lattice. Our work
opens up the study of a wide class of structural transitions and ordering
phenomena at surfaces and in low-dimensional systems.
