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Optical gain in metamaterials and plasmonic systems: From loss compensation to stimulated emission

Localized surface plasmons (resonant oscillations of free electrons in metallic nanoparticles) and surface plasmon polaritons (surface electromagnetic wave propagating along interface between metals and dielectrics) play an increasing role in a vast variety of applications, including, but not limited to sensing [1], information technology [2], and biomedical testing [3] and treatment [4]. They often determine unparalleled optical properties of metamaterials - engineered composite materials with rationally designed geometry, composition and arrangement of subwavelength building blocks - whose applications range from sub-diffraction imaging [5] and nano-scale lithography [6] to quantum optics [7] and heat management [8].