  We study the generation of collective orbital modes, their evolution, and the
characteristic non-linear optical response induced by them in a photoinduced
orbital-ordered correlated oxide using real-time simulations based on an
interacting multiband tight-binding (TB) model. The d-d optical transitions
under femtoseconds light-pulse in a orbital-ordered state excite collective
orbital modes, also known as "orbitons". The consistent inclusion of electronic
interactions and the coupling between charge, spin, and lattice degrees of
freedom in the TB-model provide a better understanding of the underlying
mechanisms of the collective orbital modes. The dynamics of Jahn-Teller
vibrational modes in the photoinduced state modify the intersite orbital
interaction, which further amplifies these orbital modes. In the presence of
weak ferroelectricity, the excitation of collective orbital modes induces a
strong THz oscillatory photocurrent which is long-lived. This suggests an
alternative way to experimentally detect quasiparticles describing such
collective modes through THz-emission studies in the photoinduced state. Our
study also elucidates that quasiparticle dynamics in improper ferroelectric
oxides can be exploited to achieve highly interesting and non-trivial
optoelectronic properties.
