Abstract
In experiment, we have found two similar double-Λ systems, which have converse absorption result. For the sake of understanding the absorption mechanisms between these two cases, we focus the primary research target on absorption mechanisms from single-Λ to double-Λ system. The research process can be divided by three parts. The first one is about the adiabatic condition. According to dark state and non-dark state analysis, double-Λ system will be decomposed to two eigen-modes. Based on the physics decomposition method, the relation between rising time from coupling light and response time is found (or we call the relation: adiabatic condition). The second part is about the energy ratio between ground state coherence and the probe light. Dark state polariton, as a quantum particle, carries the information during propagation in single-Λ and double-Λ system by ground state coherence and probe light. We use numerical calculations to prove that the energy ration between these two components of dark state polariton is related to a physical quantity η. Final part is about the designing of a conversion system with high conversion efficiency. According to previous two parts result, we are capable to design a system with negligible energy loss; finally we compare three types of conversion systems.