Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Host: J. Stähler
Monday, May 7, 2018, 11:00 am
PC Seminar Room, G 2.06, Faradayweg 4
Prof. Hrvoje Petek
Laboratory of Ultrafast Dynamics, Department of Physics and Astronomy, University of Pittsburgh, Pennsylvania
Ultrafast coherent screening response of a metal surface
The optical response that produces nearly perfect reflection has made polished metals prosaic implements of our daily lives for more the last 5000 years. The coherent, collective, plasmonic response of free electrons in a metal screens the external electromagnetic fields leading to reflections on the sub- to femtosecond time scales. The ultrafast formation of the surface screening charge density that reflects electromagnetic fields is thus a fundamental property of free electron plasmas, such as exists in metals. We investigate the coherent, screening response in Ag(111) surface by interferometric multi-photon photoemission spectroscopy. Although, the surface states of Ag(111) have been studied extensively by two-photon photoemission spectroscopy, we find additional the plasmonic responses. A coherent response, which could be due to the multipole plasmon of Ag(111), produces modulations in interferometric signals that are faster than the excitation laser pulse, in a seeming violation of the energy-time uncertainty.