Complex-frequency superlensing faces intrinsic limitations

Recent experiments [Guan et al. Science 381, 766 (2023)] have demonstrated that the resolution of superlensing slabs can be significantly enhanced with complex frequency illuminations. In this study, we introduce a novel theoretical framework for analyzing electromagnetic superlensing. The framework offers new and transparent insights. It helps clarify what resolution can be expected with complex frequency, or more generally, pulse illuminations, but it also highlights inherent limitations and tempers high expectations raised by recent electromagnetic experiments in the infrared. [accepted Optica]