Artifacts in fluorescence lifetime imaging of gold step-like nanostructures

The spontaneous emission of an excited molecule can be tailored by its environment. Modifications of the spontaneous emission rate using plasmonic structures are widely investigated for applications ranging from the near-field optics, nanophotonics, to biomedical imaging. It is possible to track the spontaneous emission rate of a dipole emitter which responds to spatial changes of the environment and therefore reflect the morphology of surface of interest. In this work, we model the fluorescence lifetime imaging of gold nanorod dimers by utilizing a single dipole emitter as a sensitive probe scanning along one dimension above the metallic nanostructures. The fluorescence lifetime is spatially mapped out as an attempt to reconstruct the corresponding images. However, it is found that the lifetime imaging is not always consistent with the real morphology of nanostructure. Artifacts in lifetime imaging may arise due to the strong coupling fields in the resonance structures. The sharpness of nanorod dimers could make spontaneous emission rate of a dipole emitter change dramatically and play a key role in artifacts. The operation frequency of a dipole emitter can also influence the lifetime and contribute to artifacts. Here, we will investigate the relation between orientations of dipole emitters and spatial profile of the image. In addition, we will address strategies to distinguish these artifacts from the real morphology and present a theoretical model based on the waveguide geometry to examine possible origins of artifacts.