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Homogeneous enhancement of electric near-field in all-dielectric metasurfaces composed of cluster-based unit cells

In order to construct a dielectric analog of spaser, we study theoretically and experimentally several configurations of cluster-based unit cells for an all-dielectric metasurface characterized by resonant conditions of the trapped mode excitation. Excitation of the trapped mode is realized by either specific displacement of particles in the cluster, or perturbation of the equidistantly spaced particles by off-centered round holes or coaxial-sector notches. It turns out that the latter approach is more advantageous for enhancement of electric near-field with homogeneous distribution in-plane of the structure and its strong localization outside the high-refractive-index dielectric particles. This feature opens prospects for realization of highly desirable subwavelength flat lasing structures based on strong near-field interaction with substances exhibiting pronounced nonlinear characteristics and properties of gain media.