Impulsive excitation of a vibrational mode of Cs on Pt(1 1 1)

We demonstrate the real time observation of coherent vibrational motions of Cs atoms adsorbed on Pt(1 1 1). A femtosecond laser pulse excites impulsively a Cs–Pt stretching mode and the subsequent evolution of the nuclear motion of Cs atoms is probed by measuring the oscillatory modulation of the second harmonic intensity of a probe pulse as a function of the pump–probe delay. The frequency and the dephasing time of the mode are found to be 2.3 THz and 1.4 ps, respectively.