报告摘要：The concept of excitons, collective excited states, is well-known in solid-state physics. It was first developed by Frenkel in the 1930’s to explain the absorption spectrum of perfect molecular crystals, in which case the excitons are simple Bloch waves of excitation. Over the years, it has become apparent that also less regular structures carry delocalized excitons, which are responsible for many of their electromagnetic properties. In this presentation, I will address two classes of such systems. The first class are molecular J-aggregates, large self-assembled structures containing up to 1000’s of molecules, which play a role in novel opto-electronic applications and natural photosynthetic systems. The second class are polypeptides and proteins, in which case collective vibrations are the excitations of interest. The irregular nature of these systems and the occurrence of fluctuations in their host, provide a complex and dynamic landscape in which the excitons are created, evolve, and decay. Study of the molecular-scale dynamics in such complex (bio-) systems has developed into an important research field. I will address the basic physics of these systems, some of their intriguing properties (such as exciton superradiance, population and phase relaxation, anomalous Stokes shift, quantum level repulsion), and discuss how (ultrafast) spectroscopies are used to detect such properties.

报告人简介：Professor Jasper Knoester received his PhD in theoretical physics at Utrecht University (The Netherlands) in 1987.After postdoctoral training in Rochester, NY, USA, he returned to The Netherlands in 1989, where he was awarded a Huygens Fellowship by the Dutch government to initiate a new field of nonlinear optical spectroscopy at the Chemistry Department of the University of Groningen. In 1993, he became full professor of Theoretical Condensed Matter Physics at the same university. His primary fields of interest are nonlinear optical spectroscopy of condensed phases and biological systems, excited state dynamics in molecular aggregates and proteins, wave propagation in inhomogeneous media, and plasmonics. In 2001/2002 he was visiting professor at the Chemistry Department of MIT (USA). Since 2003 he has been scientific director of the Zernike Institutefor Advanced Materials in Groningen. This institute has about 280 members (staff, postdocs and PhD students) and is one of only six officially recognized Centers of Excellence in The Netherlands. Professor Knoester is board member of several national and international scientific organizations.He has (co-)authored about 130 scientific papers.