Cascaded plasmonic metamaterials for phase-controlled enhancement of nonlinear absorption and refraction

The nonlinear optical properties of plasmon resonant metamaterials consisting of chains of metal nanoparticles are evaluated. Introducing particle size differences along the chains leads to the development of cascaded plasmon resonances exhibiting increased field enhancement and field confinement. The interplay among the different resonances on the structures induces a frequency-dependent enhancement of the nonlinear refractive and absorptive response of the metamaterial, ultimately providing larger nonlinear susceptibility enhancement factors with engineered complex phase. It is shown that cascaded structures can provide a figure of merit for nonlinear absorption that is more than an order of magnitude larger than that obtained in noncascaded structures. The presented approach could lead to new planar and integrated nonlinear optical modulation and switching media with improved performance compared to their noncascaded counterparts.