arXiv subjects

D. P. Tsai

Publications and source records attributed to D. P. Tsai.

8 recordsLinked to original sources

arXiv2017

Generation of Flying Electromagnetic Donuts

Transverse electromagnetic plane waves are fundamental solutions of Maxwell's equations. It is less known that a radically different type of solutions has been described theoretically, but has never been realized experimentally, that exist only in the form of short burst of electromagnetic energy propagating in free-space at the speed of light. They are distinguished from transverse waves by a donut-like configuration of electric and magnetic fields with a strong field component along the propagation direction. Here, we report that such 'Flying Donuts' can be generated from conventional pulses using a singular metamaterial converter designed to manipulate both the spatial and spectral structure of the input pulse. The ability to generate Flying Donuts is of fundamental interest, as they shall interact with matter in unique ways, including non-trivial field transformations upon reflection from interfaces and the excitation of toroidal response and anapole modes in matter, thus offering new opportunities for telecommunications, sensing, and spectroscopy.

physics.optics↗

arXiv2015

Toroidal optical activity

Optical activity is ubiquitous across natural and artificial media and is conventionally understood in terms of scattering from electric and magnetic moments. Here we demonstrate experimentally and confirm numerically a type of optical activity that cannot be attributed to electric and magnetic multipoles. We show that our observations can only be accounted for by the inclusion of the toroidal dipole moment, the first term of the recently established peculiar family of toroidal multipoles.

physics.optics↗

arXiv2014

A Random Access Reconfigurable Metamaterial and a Tunable Flat Lens

The ability to control resonant properties of individual metamolecule in a metamaterial structure will offer an ultimate freedom for dynamically shaping wavefronts of electromagnetic radiation for applications such as variable aberration corrected planar lenses, dynamic holograms and spatial intensity and phase modulators. Here we report the first demonstration of a metamaterial where resonant properties of every individual metamolecule can be continuously controlled at will thus offering an ultimate freedom in achieving a dynamic control of electromagnetic wavefront of microwave radiation. We call this a Random Access Reconfigurable Metamaterial (RARM). To achieve a RARM we created an array of cavities that were filled with liquid metal in a precise fashion using microfluidic technology. The developed RARM was used provide the first demonstration of a tunable flat lens.

physics.optics↗

arXiv2012

Non-Trivial Non-Radiating Excitation as a Mechanism of Resonant Transparency in Toroidal Metamaterials

We demonstrate theoretically and confirm experimentally a new mechanism of resonant electromagnetic transparency, which yields extremely narrow isolated symmetric Lorentzian lines of full transmission in metamaterials. It exploits the long sought non-trivial non-radiating charge-current excitation based on toroidal dipole moment, predicted to generate waves of gauge-irreducible vector potential in the complete absence of scattered electromagnetic fields.

physics.optics↗

arXiv2010

A combinatorial approach to metamaterials discovery

We report a high through-put combinatorial approach to photonic metamaterial optimization. The new approach is based on parallel synthesis and consecutive optical characterization of large numbers of spatially addressable nano-fabricated metamaterial samples (libraries) with quasi-continuous variation of design parameters under real manufacturing conditions. We illustrate this method for Fano-resonance plasmonic nanostructures arriving at explicit recipes for high quality factors needed for switching and sensing applications.

physics.optics↗

arXiv2009

Spectral collapse in ensembles of meta-molecules

We report on a new collective phenomenon in metamaterials: spectral line collapse with increasing number of the unit cell resonators (meta-molecules). Resembling the behaviour of exotic states of matter, such as Bose-Einstein condensates of excitons and magnons, this new effect is linked to the suppression of radiation losses in periodic arrays. We demonstrate experimentally spectral line collapse at microwave, terahertz and optical frequencies. It emerges as a universal and truly scalable effect underpinned by classical electromagnetic interactions between the excited meta-molecules.

physics.optics↗

arXiv2009

The light-well: A tuneable free-electron light source on a chip

The passage of a free-electron beam through a nano-hole in a periodically layered metal/dielectric structure creates a new type of tuneable, nanoscale radiation source - a 'light-well'. With a lateral size of just a few hundred nanometers, and an emission intensity of ~200 W/cm^2 such light-wells may be employed in nanophotonic circuits as chip-scale sources, or in densely packed ensembles for optical memory and display applications.

cond-mat.mes-hall↗

arXiv2006

Directed sub-wavelength imaging using a layered metal-dielectric system

We examine some of the optical properties of a metamaterial consisting of thin layers of alternating metal and dielectric. We can model this material as a homogeneous effective medium with anisotropic dielectric permittivity. When the components of this permittivity have different signs, the behavior of the system becomes very interesting: the normally evanescent parts of a P-polarized incident field are now transmitted, and there is a preferred direction of propagation. We show that a slab of this material can form an image with sub-wavelength details, at a position which depends on the frequency of light used. The quality of the image is affected by absorption and by the finite width of the layers; we go beyond the effective medium approximation to predict how thin the layers need to be in order to obtain subwavelength resolution.

physics.optics↗