Abstract-Ultrabroadband terahertz conductivity of highly doped ZnO and ITO

Ultrabroadband terahertz conductivity of highly doped ZnO and ITO Tianwu Wang, Maksim Zalkovskij, Krzysztof Iwaszczuk, Andrei V. Lavrinenko, Gururaj V. Naik, Jongbum Kim, Alexandra Boltasseva, and Peter Uhd Jepsen  »View Author Affiliations

http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-5-3-566

Optical Materials Express, Vol. 5, Issue 3, pp. 566-575 (2015)
http://dx.doi.org/10.1364/OME.5.000566

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The broadband complex conductivities of transparent conducting oxides (TCO), namely aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO), were investigated by terahertz time domain spectroscopy (THz-TDS) in the frequency range from 0.5 to 18 THz using air plasma techniques, supplemented by the photoconductive antenna (PCA) method. The complex conductivities were accurately calculated using a thin film extraction algorithm and analyzed in terms of the Drude conductivity model. All the measured TCOs have a scattering time below 15 fs. We find that a phonon response must be included in the description of the broadband properties of AZO and GZO for an accurate extraction of the scattering time in these materials, which is strongly influenced by the zinc oxide phonon resonance tail even in the low frequency part of the spectrum. The conductivity of AZO is found to be more thickness dependent than GZO and ITO, indicating high importance of the surface states for electron dynamics in AZO. Finally, we measure the transmittance of the TCO films from 10 to 200 THz with Fourier transform infrared spectroscopy (FTIR) measurements, thus closing the gap between THz-TDS measurements (0.5-18 THz) and ellipsometry measurements (200-1000 THz).

© 2015 Optical Society of America

Abstract-Metamaterial composite bandpass filter with an ultra-broadband rejection bandwidth of up to 240 terahertz

Andrew C. Strikwerda^1,a), Maksim Zalkovskij¹, Dennis Lund Lorenzen¹,

Alexander Krabbe¹, Andrei V. Lavrinenko¹ and Peter Uhd Jepsen¹


1 DTU Fotonik—Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
a) Author to whom correspondence should be addressed. Electronic mail: astr@fotonik.dtu.dk.
Appl. Phys. Lett. 104, 191103 (2014); http://dx.doi.org/10.1063/1.4875795

http://scitation.aip.org/content/aip/journal/apl/104/19/10.1063/1.4875795

We present a metamaterial, consisting of a cross structure and a metal mesh filter, that forms a composite with greater functional bandwidth than any terahertz (THz) metamaterial to date.Metamaterials traditionally have a narrow usable bandwidth that is much smaller than commonTHz sources, such as photoconductive antennas and difference frequency generation. The composite structure shown here expands the usable bandwidth to exceed that of current THz sources. To highlight the applicability of this combination, we demonstrate a series ofbandpass filters with only a single pass band, with a central frequency (f0 ) that is scalable from 0.86–8.51 THz, that highly extinguishes other frequencies up to >240 THz. The performance of these filters is demonstrated in experiment, using both air biased coherent detection and a Fourier transform infrared spectrometer (FTIR), as well as in simulation. We present equations—and discuss their scaling laws—which detail the f0 and full width at half max (Δf) of the pass band, as well as the required geometric dimensions for their fabrication using standard UVphotolithography and easily achievable fabrication linewidths. With these equations, the geometric parameters and Δf for a desired frequency can be quickly calculated. Using thesebandpass filters as a proof of principle, we believe that this metamaterial composite provides the key for ultra-broadband metamaterial design.

Abstract-Graphene hyperlens for terahertz radiation

http://arxiv.org/abs/1209.3951
Andrei Andryieuski, Andrei V. Lavrinenko, Dmitry N. Chigrin

We propose a graphene hyperlens for the terahertz (THz) range. We employ and numerically examine a structured graphene-dielectric multilayered stack that is an analogue of a metallic wire medium. As an example of the graphene hyperlens in action we demonstrate an imaging of two point sources separated with distance $\lambda_{0}/5$. An advantage of such a hyperlens as compared to a metallic one is the tunability of its properties by changing the chemical potential of graphene. We also propose a method to retrieve the hyperbolic dispersion, check the effective medium approximation and retrieve the effective permittivity tensor.