Generalized Transition Moment and Oscillator Strength for Optimal Control of Excited States Using Near-Field Light

The near field is a highly localized light field that is present in the vicinity of materials. It holds considerable potential for manipulating molecular excitation through the design of nanostructures. To that end, a simple yet applicable computational method is required. This letter presents an optimization strategy to achieve targeted electronic excitation in molecules using near-field light. The generalized transition moment and oscillator strength based on the multipolar Hamiltonian can incorporate key parameters affecting the near field, including shape, size, and material composition. This calculation helps optimize electronic transitions through manipulation of the aforementioned parameters. The feasibility of the proposed scheme was demonstrated using a scanning tunneling microscopic setup with light, wherein the near field is controlled by varying the tip position in two dimensions. This approach paves the way for further innovations, which may ultimately enable precise control of molecular behavior by using tailored near-field interactions.