nanocavities

Nanocavities are optical resonators with dimensions on the nanometer to micrometer scale that confine light to subwavelength volumes. By supporting discrete resonant modes, they generate strong local electromagnetic fields and enable enhanced light–matter interaction. The principal figures of merit are the quality factor Q, which measures how long energy remains in the cavity, and the mode volume V, which characterizes the spatial confinement of the mode. The Purcell factor, which describes the enhancement of spontaneous emission for an emitter placed in the cavity, scales with Q/V and depends on the wavelength and refractive index.

There are two broad families of nanocavities. Dielectric nanocavities employ high-index, low-loss materials such as silicon, silicon nitride, or gallium arsenide and can achieve high Q with relatively modest losses. Examples include photonic crystal cavities, dielectric micropillars, and whispering-gallery-mode resonators. Plasmonic nanocavities use metals like gold or silver to confine fields below the diffraction limit, achieving extremely small mode volumes but with higher intrinsic losses. Hybrid cavities combine dielectric and plasmonic elements to balance confinement and quality factor.

Fabrication methods include top-down approaches such as electron-beam lithography, reactive ion etching, and focused ion beam milling, as well as bottom-up techniques like colloidal synthesis and self-assembly. Materials span semiconductors, dielectrics, and metals, with applications across sensing, quantum optics, single-photon sources, nonlinear optics, and nanolasers. Ongoing challenges involve mitigating losses, achieving precise spectral control, and integrating nanocavities with larger photonic systems.