Lattice dynamics and electronic Gruneisen parameters of femtosecond laser-excited bismuth

In this study, we probed the lattice dynamics of bismuth subjected to femtosecond laser irradiation by ultrafast electron diffraction. The changes in the diffraction intensity and angle were determined. The lattice exhibited compression upon laser excitation, followed by expansion with damped vibrations. Coherent acoustic phonons were observed as oscillations in the lattice spacing. The results were analyzed using a damped harmonic oscillator model where the hot electrons caused the blast compressive force, which resulted in lattice-spacing oscillation for the expanded lattice following the compression. We obtained the rate of electron-phonon coupling, its anisotropy, and the Gruneisen parameters of the electronic subsystem.