  We investigate the excitation of phonons in photoexcited antimony and
demonstrate that the entire electron-lattice interactions, in particular
coherent and incoherent electron-phonon coupling, can be probed simultaneously.
Using femtosecond electron diffraction (FED) with high temporal resolution, we
observe the coherent excitation of the fully symmetric \Ag\ optical phonon mode
via the shift of the minimum of the atomic potential energy surface. Ab initio
molecular dynamics simulations on laser excited potential energy surfaces are
performed to quantify the change in lattice potential and the associated
real-space amplitude of the coherent atomic oscillations. Good agreement is
obtained between the parameter-free calculations and the experiment. In
addition, our experimental configuration allows observing the energy transfer
from electrons to phonons via incoherent electron-lattice scattering events.
The electron-phonon coupling is determined as a function of electronic
temperature from our DFT calculations and the data by applying different models
for the energy-transfer.
