  We theoretically investigate pump-probe optical responses in the
two-dimensional extended Hubbard model describing cuprates by using a
time-dependent Lanczos method. At half filling, pumping generates photoinduced
absorptions inside the Mott gap. A part of low-energy absorptions is attributed
to the independent propagation of photoinduced holons and doublons. The
spectral weight just below the Mott gap increases with decreasing the on-site
Coulomb interaction $U$. We find that the next-nearest-neighbor Coulomb
interaction $V_1$ enhances this $U$ dependence, indicating the presence of
biexcitonic contributions formed by two holon-doublon pairs. Photo-pumping in
hole-doped systems also induces spectral weights below remnant Mott-gap
excitations, being consistent with recent experiments. The induced weights are
less sensitive to $V_1$ and may be related to the formation of a biexcitonic
state in the presence of hole carriers.
