Emission rate studying through nanodiamonds with embedded nitrogen vacancy centers

High-refractive index nanoparticles, including diamond nanoparticles, can exhibit strong optical resonances, whose spectral position depends on particle size and shape. In this work we demonstrate that these resonances can be used to control the emission of active defects within the particles. We present the theoretical concept of an active dielectric nanoantenna, and study the dependence of the radiation properties on the position of the defect within the particle, as well as on particle size.This work was supported by the Ministry of Education and Science of Russian Federation (Project 2.2267.2017/4.6) and Russian Foundation for Basic Research (Grant No. 18-37- 00384, 16- 29- 05317)

Nonlinear polaritons in a monolayer semiconductor coupled to optical bound states in the continuum

Optical bound states in the continuum (BICs) provide a way to engineer very narrow resonances in photonic crystals. The extended interaction time in these systems is particularly promising for the enhancement of nonlinear optical processes and the development of the next generation of active optical devices. However, the achievable interaction strength is limited by the purely photonic character of optical BICs. Here, we mix the optical BIC in a photonic crystal slab with excitons in the atomically thin semiconductor MoSe2 to form nonlinear exciton-polaritons with a Rabi splitting of 27 meV, exhibiting large interaction-induced spectral blueshifts. The asymptotic BIC-like suppression of polariton radiation into the far field toward the BIC wavevector, in combination with effective reduction of the excitonic disorder through motional narrowing, results in small polariton linewidths below 3 meV. Together with a strongly wavevector-dependent Q-factor, this provides for the enhancement and control of polariton–polariton interactions and the resulting nonlinear optical effects, paving the way toward tuneable BIC-based polaritonic devices for sensing, lasing, and nonlinear optics

Theory, observation, and ultrafast response of the hybrid anapole regime in light scattering

Modern nanophotonics has witnessed the rise of "electric anapoles" (EDAs), destructive interferences of electric and toroidal electric dipoles, actively exploited to resonantly decrease radiation from nanoresonators. However, the inherent duality in Maxwell equations suggests the intriguing possibility of "magnetic anapoles," involving a nonradiating composition of a magnetic dipole and a magnetic toroidal dipole. Here, a hybrid anapole (HA) of mixed electric and magnetic character is predicted and observed experimentally via dark field spectroscopy, with all the dominant multipoles being suppressed by the toroidal terms in a nanocylinder. Breaking the spherical symmetry allows to overlap up to four anapoles stemming from different multipoles with just two tuning parameters. This effect is due to a symmetry-allowed connection between the resonator multipolar response and its eigenstates. The authors delve into the physics of such current configurations in the stationary and transient regimes and explore new ultrafast phenomena arising at sub-picosecond timescales, associated with the HA dynamics. The theoretical results allow the design of non-Huygens metasurfaces featuring a dual functionality: perfect transparency in the stationary regime and controllable ultrashort pulse beatings in the transient. Besides offering significant advantages with respect to EDAs, HAs can play an essential role in developing the emerging field of ultrafast resonant phenomena