Nonlinear Circular Dichroism in the Second-Harmonic Generation from AlGaAs Nanoparticle Dimers

Here we study the nonlinear response of a nanoparticle dimer illuminated by a circularly polarized light. We observe, for the first time to our knowledge, nonvanishing circular dichroism of the second - harmonic signal due to the interplay of multipolar magnetic and electric Mie resonances provided the dimer axes is oriented under an angle to the crystalline lattice of the dielectric material. We develop a general formalism and modal theory to explain the origin of this unexpected phenomenon and verify our general theory by some experimental results for the resonant second harmonic generation (SHG) from the AlGaAs dimers placed on an engineering substrate. Our results show that Mie-resonant AlGaAs nanoparticles combined into a dimer with an arbitrarily oriented [100] crystalline lattice indeed reveal a non-zero and nonvanishing circular dichroism of the second harmonic signal.