  We investigated the nonequilibrium electronic structure of 2H-NbSe$_2$ by
time- and angle-resolved photoemission spectroscopy. We find that the band
structure is distinctively modulated by strong photo-excitation, as indicated
by the unusual increase in the photoelectron intensities around E$_F$. In order
to gain insight into the observed photo-induced electronic state, we performed
DFT calculations with modulated lattice structures, and found that the
variation of the Se height from the Nb layer results in a significant change in
the effective mass and band gap energy. We further study the momentum-dependent
carrier dynamics. The results suggest that the relaxation is faster at the
K-centered Fermi surface than at the $\Gamma$-centered Fermi surface, which can
be attributed to the stronger electron-lattice coupling at the K-centered Fermi
surface. Our demonstration of band structure engineering suggests a new role
for light as a tool for controlling the functionalities of solid-state
materials.
