  Ultrafast dynamics across the photoinduced three-dimensional Peierls-like
insulator-metal (IM) transition in CuIr$_{2}$S$_{4}$ was investigated by means
of the all-optical ultrafast multi-pulse time-resolved spectroscopy. The
structural coherence of the low-$T$ broken symmetry state is strongly
suppressed on a sub-picosecond timescale above a threshold excitation fluence
of $F_{\mathrm{c}}\approx3$ mJ/cm$^{2}$ (at 1.55-eV photon energy) resulting in
a structurally inhomogeneous transient state which persists for several-tens of
picoseconds before reverting to the original low-$T$ state. The electronic
order shows a transient gap filling at a significantly lower fluence threshold
of $\sim0.6$~mJ/cm$^{2}$. The data suggest that the photoinduced-transition
structural dynamics to the high-$T$ metallic phase is governed by
first-order-transition nucleation kinetics that prevents the complete
structural transition into the high-$T$ phase even at excitation fluences
significantly larger than $F_{\mathrm{c}}$. In contrast, the
dynamically-decoupled electronic order is suppressed rather independently due
to a photoinduced Mott transition.
