  Photoinduced dynamics in an excitonic insulator is studied theoretically by
using a two-orbital Hubbard model on the square lattice where the excitonic
phase in the ground state is characterized by the BCS-BEC crossover as a
function of the interorbital Coulomb interaction. We consider the case where
the order has a wave vector $Q=(0,0)$ and photoexcitation is introduced by a
dipole transition. Within the mean-field approximation, we show that the
excitonic order can be enhanced by the photoexcitation when the system is
initially in the BEC regime of the excitonic phase, whereas it is reduced if
the system is initially in the BCS regime. The origin of this difference is
discussed from behaviors of momentum distribution functions and
momentum-dependent excitonic pair condensation. In particular, we show that the
phases of the excitonic pair condensation have an important role in determining
whether the excitonic order is enhanced or not.
