Amplitude beating of coherent phonon in graphite under high intensity photo-excitation

Femtosecond dynamics of coherent E2g1 phonon of graphite under high density photo-excitation is investigated by time-resolved reflectivity measurements. Both at low and room temperatures we found the amplitude beating of the coherent phonon, which appears similar to the amplitude collapse and revival of the coherent A1g phonon of bismuth. Our analysis indicates that the amplitude beating in graphite originates from two (or three) almost classical oscillators, which is in contrast to the more quantum collapse-revival in bismuth. Possible mechanisms for the amplitude beating in graphite are discussed.