Nonlinear Spectroscopy on the Plasmonic Analog of Electromagnetically Induced Absorption: Revealing Minute Structural Asymmetries

Tailoring not only the linear but also the nonlinear properties of plasmonic structures has been a longstanding idea. The plasmonic dolmen structure with its many degrees of freedom in design has been of particular interest. We are investigating this system in detail in the retarded weak-coupling regime, the so-called plasmonic analog of electromagnetically induced absorption. While it is generally expected that the enhanced absorbance leads to an increased nonlinear generation, we find that the details are more complex. A thorough wavelength and polarization resolved study reveals two distinct nonlinear contributions. Our nonlinear spectroscopy method exhibits a surprisingly high sensitivity to minute structural asymmetries. Our experimental results are corroborated by finite-element simulation. We envision that our findings will stimulate further research into phase tuning, structural symmetries, and manipulation in nonlinear plasmonic systems in order to fully exploit the ability to tailor the linear a...