Femtosecond formation of phonon-plasmon coupled modes studied by ultrabroadband THz spectroscopy

Abstract

The ultrafast transition of an optical phonon resonance to a coupled phonon-plasmon system is studied. After 10-fs photoexcitation of i-InP, the buildup of coherent beats of the emerging hybrid modes is directly monitored by means of ultrabroadband THz spectroscopy. Mutual repulsion and redistribution of the oscillator strength of the interacting phonons and plasmons is seen to emerge within approximately one oscillation cycle of the upper branch of the mixed modes.