Nonlinear optical activity measurement spectroscopy of coupled multi-chromophore systems

A theoretical description of two-dimensional circularly polarized photon echo (2D CP PE) spectroscopy, which is an extension of the photon echo spectroscopy, is presented. The CP PE is a differential photon echo spectroscopy utilizing left- and right-circularly polarized beam and is a nonlinear optical activity measurement tool for studying chiral molecule and coupled multi-chromophore system. Particularly, the latter is mainly considered here and it is shown that the detailed excitation transfer pathways of an electronically coupled multi-chromophore system can be revealed by examining the time-resolved 2D CP PE spectrum. The Fenna-Matthews-Olson light-harvesting complex is considered in detail to demonstrate the advantages and characteristic differences of the CP PE method in comparison to other linear and nonlinear optical spectroscopic techniques.