Nonlinear optics and spectroscopy 19 Excitons and polaritons CHAPTER II. THEORY Electronic Energy Transfer Percolation, random walks, and clusters Stochastic Liouville equation and Grover-Silbey approaches Generalized master equation Polariton Fusion Theory CHAPTER III. EXPERIMENTAL Sample Preparation and Analysis Laser System and Optics Data Acquisition and Control CHAPTER IV. RESULTS AND DISCUSSION Electronic Energy Transfer Coherent and incoherent transfer Coherence length Migration time vs. trapping time Capture limited regime vs. migration limited regime Branching ratios 68