A Tentative Comprehensive Overview of the Second Harmonic Generation from Plasmonic Nanoparticles

Abstract

We report in this work a detailed analysis of the competition that takes place between size and symmetry in the second harmonic generation (SHG) response from nanoparticles. SHG, the physical phenomenon entailing the conversion of two photons at a fundamental frequency into a single photon at the harmonic frequency is highly sensitive to symmetry. SHG is indeed forbidden in centrosymmetric materials within the electric dipole approximation. This feature can be exhibited by nanoparticles at the level of their material crystalline structure or their nanoparticle shape. Furthermore, the electric dipole approximation breaks down as the nanoparticles size increases. It is therefore critical to assess carefully both, i.e. material and shape symmetry as well as size, to fully uncover the SHG response from these nanoscale systems.After a discussion on the specific features of the SHG response in nanoparticles at the nanoscale, nanoparticles are classified according to the centrosymmetry or non centrosymmetry of the material they are made of and their geometrical shape. Finally, the role of size in the breaking of the electric dipole approximation is discussed.