Optical Characterization of Plasmonic Metamaterials

Optical metamaterials are artificially engineered structures composed of subwavelength units. They exhibit exotic optical properties that are unobserved or unattainable in nature. Recent efforts have led to the observation of many interesting phenomena and as well aspromising applications such as super-resolution imaging and transformation optics. At optical frequencies, the functionalities of metamaterials are achieved through excitation of plasmons as most structures are metal-dielectric composites. The objective of this dissertation is to provide the tools and study the unique properties and novel phenomena of plasmonic metamaterials. We first theoretically study a pair of nanobars to properly understand artificial magnetism which is important in most metamaterials. Then we experimentally investigate the optical properties of the "fishnet" metamaterial using a variety of spectroscopic techniques. First, we probe the plasmonic band structure using angle- and polarization- resolved linear spectroscopy. Most interestingly, we observe dark magnetic modes and their coupling to bright modes leading to avoid-crossing behavior typical of quantum systems. The k-dependent effective optical constants are measured through phase measurements confirming the dispersion of the magnetic resonance. Second, second-harmonic generation spectroscopy is carried out showing significant resonance enhancement achieved through the excitation of plasmons. The observations are substantiated with theory to validate our physical understanding of nonlinear wave-mixing processes in metamaterials. Finally, we carry out pump-probe spectroscopy to understand the dynamic behavior. The optical responses are shown to be modulated in femtosecond time scale. The modulation magnitude is greatly enhanced while the dynamics is mainly determined by the constituting dielectric medium