Near-Field spectroscopy of Photonic Crystal Cavities characterized by Fano Local Density of States

Microcavities and nanoresonators are characterized by their quality factors (Q) and mode volumes (V). While Q is unambiguously defined, there are questions on V and, in particular, on its complex-valued character, whose imaginary part is linked to the non-Hermitian nature of open systems. The complex modal volume implies a deep revision of the Purcell factor expression, with counterintuitive effects, such as non-Lorentzian local density of states. We experimentally demonstrate these predictions in coupled photonic crystal cavities with low optical losses.