Abstract-Characterization of an active metasurface using terahertz ellipsometry

Nicholas Karl, Martin S. Heimbeck,   Henry O. Everitt,   Hou-Tong Chen, Antoinette J. Taylor, Igal Brener, Alexander Benz, John L. Reno, Rajind Mendis,  Daniel M. Mittleman,

http://aip.scitation.org/doi/abs/10.1063/1.5004194

Switchable metasurfaces fabricated on a doped epi-layer have become an important platform for developing techniques to control terahertz (THz) radiation, as a DC bias can modulate the transmission characteristics of the metasurface. To model and understand this performance in new device configurations accurately, a quantitative understanding of the bias-dependent surface characteristics is required. We perform THz variable angle spectroscopic ellipsometry on a switchable metasurface as a function of DC bias. By comparing these data with numerical simulations, we extract a model for the response of the metasurface at any bias value. Using this model, we predict a giant bias-induced phase modulation in a guided wave configuration. These predictions are in qualitative agreement with our measurements, offering a route to efficient modulation of THz signals.

Abstract-Screening effects in metal sculptured thin films studied with terahertz Mueller matrix ellipsometry

• T. Hofmann^{a, b, c, ,} , 
• S. Knight^b, 
• D. Sekora^b, 
• D. Schmidt^b, 
• C.M. Herzinger^d, 
• J.A. Woollam^d, 
• E. Schubert^b, 
• M. Schubert^b, c

• ^a Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, U.S.A
• ^b Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, U.S.A.
• ^c Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
• ^d J.A. Woollam Co. Inc. 645 M Street, Suite 102, Lincoln, NE 68508, U.S.A.
• 
  

http://www.sciencedirect.com/science/article/pii/S0169433216329324

The anisotropic optical dielectric functions of a metal (cobalt) slanted columnar thin film deposited by electron-beam glancing angle deposition are reported for the terahertz (THz) frequency domain before and after the slanted columnar thin film was passivated by a conformal alumina coating. A simple effective medium dielectric function homogenization approach which describes isolated, electrically conductive columns rendering the thin film biaxial (orthorhombic) is used to model the observed optical responses. Upon passivating the slanted columnar thin film with a 3 nm thick alumina film an increase of both the real and the imaginary part of the dielectric function for all major polarizability directions is found and attributed to screening effects within the spatially coherent metal nanocolumns.

Abstract-Developments in THz-Range Ellipsometry: Quasi-Optical Ellipsometer

(Authors not listed)

http://ieeexplore.ieee.org/xpl/abstractKeywords.jsp?arnumber=7416254&filter%3DAND%28p_IS_Number%3A5741778%29

A novel experimental setup for multiangular ellipsometric measurements in terahertz spectral range 0.1– $hbox{1 THz}$ is described. The instrument operates in polarizer-compensator-sample-analyzer configuration and allows various measurement schemes (e.g., null and rotating analyzer). The ellipsometer is based on quasi-optical transmittance line—hollow dielectric beamguide (HDB)—and oa kit of HDB-based components that provided main advantages of the ellipsometer as compared with known analogs. HDB provides almost flat phase front of the radiation on the entire channel cross section without any lenses or mirrors. Ultra-broadband quasi-optical transmittance line provides operation of the ellipsometer within 0.1–$hbox{1 THz}$ frequency range without any modifications of configuration and/or construction. This setup can be assembled/disassembled very easily (as a LEGO meccano) and is easily integrated into other equipment. Experimental testing of the ellipsometer was carried out by comparing dielectric constants of a set of materials measured by the setup with reference data and with the results of independent reflectometry measurements.