Dynamic bound states in the continuum

All-dielectric metasurfaces are a versatile platform to investigate a host of unconventional physical scattering responses. Effects, including high absorption and Huygens’ surfaces, have been demonstrated; however, a more exotic materialization—termed bound states in the continuum (BSCs)—exists and consists of nonradiating localized waves that lie within the energy spectrum of the continuum. Here we experimentally demonstrate a dynamic BSC at terahertz frequencies that realizes a material-limited high-quality factor (𝑄) resonance 𝑄=8.7×103, which may be modified by over 2 orders of magnitude through photodoping with band gap light. We elucidate the nature of the BSC resonance, and our experimental results are well supported by eigenvalue and 𝑆-parameter simulations. The demonstrated system and underlying theory establish a path to realize extremely high-𝑄 dynamic resonances, which may be useful for detection of hazardous materials and frequency-diverse imaging.