  Transient single-particle spectral function of BaFe$_{2}$As$_{2}$, a parent
compound of iron-based superconductors, has been studied by time- and
angle-resolved photoemission spectroscopy with an extreme-ultraviolet laser
generated by higher harmonics from Ar gas, which enables us to investigate the
dynamics in the entire Brillouin zone. We observed electronic modifications
from the spin-density-wave (SDW) ordered state within $\sim$ 1 ps after the
arrival of a 1.5 eV pump pulse. We observed optically excited electrons at the
zone center above $E_{F}$ at 0.12 ps, and their rapid decay. After the fast
decay of the optically excited electrons, a thermalized state appears and
survives for a relatively long time. From the comparison with the
density-functional theory band structure for the paramagnetic and SDW states,
we interpret the experimental observations as the melting of the SDW.
Exponential decay constants for the thermalized state to recover back to the
SDW ground state are $\sim$ 0.60 ps both around the zone center and the zone
corner.
