  We study ultrafast x-ray diffraction on the charge density wave (CDW) of
SmTe$_3$ using an x-ray free electron laser. The CDW peaks show that
photoexcitation with near-infrared pump centered at 800 nm generates domain
walls of the order parameter propagating perpendicular to the sample surface.
These domain walls break the CDW long range order and suppress the diffraction
intensity of the CDW for times much longer than the $\sim 1$~ps recovery of the
local electronic gap. We reconstruct the spatial and temporal dependence of the
order parameter using a simple Ginzburg-Landau model and find good agreement
between the experimental and model fluence dependences. Based on the model we
find that at long times, depending on the pump fluence, multiple domain walls
remain at distances of few nm from the surface.
