T.S. Kao

Nanohole Array as a Lens

We demonstrate that a quasi-crystal array of nanoholes in a metal screen can mimic a function of the lens: one-to-one imaging of a point source located a few tens of wavelengths away from the array to a point on the other side of the array. A displacement of the point source leads to a linear displacement of the image point. Complex structures composed of multiple point sources can be faithfully imaged with resolutions comparable to those of high numerical aperture lenses.

Coherent control of nanoscale light localization in metamaterial: creating and positioning isolated subwavelength energy hot spots.

We show the strong optically induced interactions between discrete metamolecules in a metamaterial system and coherent monochromatic continuous light beam with a spatially tailored phase profile can be used to prepare a subwavelength scale energy localization. Well-isolated energy hot spots of a fraction of a wavelength can be created and positioned on the metamaterial landscape offering new opportunities for data storage and imaging applications.

Metamaterial as a controllable template for nanoscale field localization

We report that subwavelength localization of light in the near-field of a double-periodic photonic metamaterial may be efficiently controlled by the polarization and wavelength of the incident radiation. A dramatic variation in the periodic near-field landscapes, including a transition from a pattern of isolated subwavelength plasmon hot-spots to a blurred, low contrast pattern, accompanied by a change in the pattern’s symmetry has been observed in the proximity of an aluminum nanowire “fish-scale” nanostructure. Hot-spots as small as 0.23λ have been achieved and their position has been controlled by tuning the wavelength of incident light across the dipole absorption resonance of the metamaterial. A simple switch of the polarization state can lead to a spatial period doubling in the landscape pattern.

Coherent control of nanoscale light localization: Creating and positioning isolated sub-wavelength energy hot-spots

We suggest a new paradigm for achieving prescribed localization of optical energy with nanoscale accuracy. Well isolated energy hot-spots as small as λ/10 can be created and positioned at the chosen meta-molecules on the metamaterial landscape.

Superresolution without evanescent fields

The last decade has seen numerous efforts to achieve imaging resolution beyond that of the Abbe-Rayleigh diffraction limit. The main direction of research aiming to break this limit seeks to exploit the evanescent components containing fine detail of the electromagnetic field distribution at the immediate proximity of the object. Here we propose a solution that removes the need for evanescent fields. The object being imaged or stimulated with sub-wavelength accuracy does not need to be in the immediate proximity of the superlens or field concentrator: an optical mask can be designed that creates constructive interference of waves known as superoscillation, leading to a sub-wavelength focus of prescribed size and shape in a field of view beyond the evanescent fields, when illuminated by a monochromatic wave. We demonstrate that such a mask may be used not only as a focusing device, but also as a super-resolution imaging device.

Fractional Talbot effect in a dielectric micro-spheres array

A hexagonal array of dielectric micro-spheres can work as diffraction-limited or super-resolution lens array. The fractional Talbot effect is obvious for those diffraction-limited foci, but is not well-defined for the super-resolution foci.