Mode-selective excitation of coherent surface phonons on alkali-covered metal surfaces

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Abstract
We demonstrate the mode-selective excitation of coherent phonons at Pt(111) surfaces covered with submonolayer caesium atoms. A burst of 150 fs laser pulses with the repetition rate of 2.0–2.9 THz was synthesized by using a spatial-light modulator, and used for the coherent surface phonon excitation. The coherent nuclear motion was monitored by time-resolved second harmonic generation. By tuning the repetition rate, we succeeded in controlling the relative amplitude of the vibrational coherence of the Cs–Pt stretching mode (2.3–2.4 THz) to that of the Pt surface Rayleigh phonon mode (2.6 or 2.9 THz, depending on the Cs coverage).