Ultrafast photo-activation of surface polaritons in black phosphorus heterostructures

Surface polaritons, which emerge from the coupling between collective electronic motion with mid-infrared photons, have made two-dimensional materials a versatile platform for nanophotonics [1,2]. Apart from the well-studied plasmonic material graphene, semiconducting layered compounds and heterostructures hold new promise for high-contrast, ultrafast control of polaritons. Here, we report on tailored structures based on black phosphorus and SiO2 with favorable properties for ultrafast nanophotonics [3]. We use femtosecond mid-infrared near-field microscopy to photo-activate a hybrid surface phonon-plasmon polariton that is nonexistent in the unexcited sample and trace its mode structure in time, energy and space. We find that the mode shows excellent coherence and is strongly confined in energy and momentum throughout its lifetime of ~5 ps. These properties combined with the superior switching speed of ~50 fs render it a promising candidate for ultrafast nano-optical devices. © OSA 2017.