Hyperbolic metamaterials, a class of artificially engineered materials with a highly anisotropic permittivity response originating from opposite signs of the principal components of the electric tensor, have attracted significant interest in recent years due to their ability to manipulate the propagation light in exotic ways [1]. Such materials enable distinctive optical phenomena such as negative refraction, super-resolution imaging, and enhanced spontaneous emission. Here we exploit the hyperbolic iso-frequency characteristic of a planar type-II HMM (composed of a template-stripped [2] stack of alternating, 25-nm-thick, sputtered films of Ag and SiO2) to achieve high-sensitivity proximity detection of nanoparticles in transmission. The iso-frequency surface of the HMM is unique in that propagation of light over the entire visible-range is allowed only for electromagnetic modes having tangential spatial frequencies kx exceeding the free-space wavevector k0 by over a factor of two (kx t 2k0) [3,4]. Due to its high sensitivity to nanoparticles in deep-subwavelength proximity to a surface, achieved without the use of dark-field optics, this HMM-based device hints at promising applications in bio-chemical sensing, particle tracking and contamination analysis. Template-stripped refractive-index-change sensors consisting of ultra-high quality factor open-cavity resonators for surface-plasmon polaritons will also be discussed.
1) A. Poddubny et al. “Hyperbolic metamaterials,” Nat. Photon. 7, 958 (2013). 2) P. Nagpal et al. “Ultrasmooth Patterned Metals for Plasmonics and Metamaterials,” Science 325, 594 (2009). 3) T. U. Tumkur et al. “Control of reflectance and transmittance in scattering and curvilinear hyperbolic meatamaterials,” Appl. Phys. Lett. 101, 091105 (2012). 4) T. Xu & H.J. Lezec, “Visible-frequency asymmetric transmission devices incorporating a hyperbolic metamaterial,” Nat. Comm. 5, 4141 (2014).
hlezec@nist.gov