Abstract-Terahertz All-Dielectric Magnetic Mirror Metasurfaces

Zhijie Ma, Stephen M. Hanham, Pablo Albella, Binghao Ng, Hsiao Tzu Lu, Yandong Gong, Stefan A. Maier and Minghui Hong

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.6b00096?journalCode=apchd5

We demonstrate an all-dielectric metasurface operating in the terahertz band that is capable of engineering a reflected beam's spatial properties with high efficiency. The metasurface is formed from an array of silicon cube resonators which simultaneously support electric and magnetic dipolar Mie resonances. By controlling the interference between these modes, the amplitude and phase of a reflected wave can be arbitrarily controlled over a sub-wavelength area. We demonstrate the flexibility and utility of this metasurface by optimizing the surface to produce several reflected beam types including vortex and Bessel beams; the latter being useful for diffraction-free point-to-point terahertz communications. Additionally, we show theoretically and experimentally how the metasurface can produce an all-dielectric magnetic mirror in the terahertz band.

Abstract-Broadband Terahertz Sensing on Spoof Plasmon Surfaces

Binghao Ng , Stephen M. Hanham , Jianfeng Wu ,Antonio I. Fernández-Domínguez , Norbert Klein ,Yun Fook Liew , Mark B.H. Breese , Minghui Hong, and Stefan A. Maier

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/ph500272n

Publication Date (Web): September 2, 2014

Copyright © 2014 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/ph500272n


In this paper, we show that broadband spectral data can be experimentally extracted from corrugated metallic surfaces consisting of a linear array of subwavelength grooves supporting tightly confined spoof plasmons. Using a combination of the scattering edge coupling method and short-time Fourier transform, we are able to discern the group velocity characteristics of a spoof plasmon pulse which in turn allows for the extraction of broadband dispersion data from 0.4 THz to 1.44 THz in a single measurement. Refractive index sensing of various fluids is demonstrated at microlitre volume quantities by monitoring changes in not only the dispersion relation but also the frequency dependent attenuation of the spoof plasmons. This gives information about both the real and imaginary part of the refractive index of an analyte, indicating the potential for spoof plasmon surfaces to fully characterise substances in the terahertz regime. Lastly, we show that the strong electromagnetic field confinement near the effective spoof plasmon frequency allows for surface enhanced absorption spectroscopy, demonstrated here with α-lactose monohydrate powder. This allows us to take a more spectroscopic approach to THz sensing whereby substances can be uniquely identified by their spectral fingerprints. The enhanced light-matter interactions that occur in the vicinity of the spoof plasmon surface allows for a more efficient use of the limited power of current terahertz sources. Together with the ability to integrate spoof plasmon surfaces with microfluidics and to freely design its electromagnetic properties, we believe that these surfaces can be a very versatile platform on which chip-scale terahertz sensing can be performed.

Abstract-Free-standing terahertz chiral meta-foils exhibiting strong optical activity and negative refractive index

Jianfeng Wu¹, Binghao Ng², Shuvan P. Turaga¹, Mark B. H. Breese^1,3, Stefan A. Maier², Minghui Hong⁴, Andrew A. Bettiol¹, and Herbert O. Moser^5
1Department of Physics, Center for Ion Beam Applications (CIBA), National University of Singapore, 2 Science Drive, Singapore 
²Department of Physics, Imperial College, London SW7 2AZ, United Kingdom 
³Singapore Synchrotron Light Source (SSLS), National University of Singapore, 5 Research Link, 117603 Singapore 
⁴Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576 Singapore 
⁵Karlsruhe Institute of Technology (KIT), Network of Excellent Retired Scientists (NES), and Institute of Microstructure Technology (IMT), Postfach 3640, 76021 Karlsruhe, Germany 

http://apl.aip.org/resource/1/applab/v103/i14/p141106_s1?isAuthorized=no

A chiral meta-foil consisting of a self-supported square array of interconnected conjugated rosettes is demonstrated at terahertz frequencies. It exhibits strong optical activity and circular dichroism. Negative refractive index with a figure-of-merit as high as 4.2 is achieved, attributed to its free-standing nature. Experimental results are in good agreement with numerical simulation. Free-standing chiral meta-foils provide a unique approach to create a completely all-metal chiral metamaterial, which can be flexibly integrated into optical setups while eliminating dielectric insertion losses.

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