Optical control of coherent lattice motions probed by femtosecond electron diffraction.

We report the study of laser-induced coherent lattice motions using femtosecond electron diffraction. The oscillations of Bragg peak positions associated with a damped lattice vibration along the surface normal were directly observed in real time and with sub-milli-angstrom spatial resolution. In addition, by using a pair of optical excitation pulses and varying their time delay and relative pulse intensities, we demonstrated the successful control of coherent lattice motions.