Observation of spectrally continuous resonance enhancement by mode coalescence

Microcavities rarely operate in a broadband regime and are, therefore, limited in their ability to resonantly enhance broadband light-matter interactions. Here, we present what is believed to be the first experimental demonstration of several overlapping spectrally continuous optical resonances. We rely on sufficiently long cylinders here, making the mode's axial quantum numbers turn from a discrete set into a continuous one. Except for potential perfect absorbers of white light and bright white microemitters, other waves in nature (e.g., sound, matter waves, and quantum probability densities) might similarly support perfect absorption of earthquakes, energy harnessing from sea waves, and fundamental studies in wave-matter interaction.