Saturable Absorption Enchantment of Au Nanorods Based on Energy Transfer between Longitudinal and Transverse Energy Levels

Four kinds of Au nanorods (NRs) with different aspect ratios are designed to adjust the relationship between resonance energy level of longitudinal (L) and transverse (T) modes. During the femto-second Z-scan experiments, huge saturable absorption phenomena are observed while the energy level T is located between one to two times of the energy level L. This means that the energy may transfer between longitudinal and transverse energy levels in the same and/or different Au NRs. It effectively depresses the production of revised saturated absorption and increases the saturable absorption efficiency. This method is significant for the preparation of high-efficiency saturable absorption devices.