An active metallic nanomatryushka with two similar super-resonances

The optical properties of a simple metallic nanomatryushka (nanosphere-in-a-nanoshell) with gain have been investigated theoretically. The spaser (surface plasmon amplification by stimulated emission of radiation) phenomena can be observed at two critical wavelengths in the active metallic nanomatryushkas. With increasing the gain coefficient of the middle layer, a similar super surface plasmon (SP) resonance is first found at the omega(-) (+)vertical bar(1) mode of the active nanoparticles and then breaks down. With further increasing the gain coefficient, another similar super-resonance occurs at the omega(-) (-)vertical bar(1) mode. The near-field enhancements in the active nanomatryushkas also have been greatly amplified at the critical wavelengths for omega(-) (+)vertical bar(1) and omega(-) (-)vertical bar(1) modes. It is further found that the amplifications of SPs in the active Ag-SiO2-Au nanoshell are strongest in four kinds of nanoshells and hence the largest near fields. The giant near-field enhancement can greatly enhance the Raman excitation and emission. (C) 2014 AIP Publishing LLC.