Self-Referenced Meaurements of the Terahertz Dielectric Properties of Metals via Excitation of Surface Plasmon-Polaritons

Shashank Pandey Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah, USA Barun Gupta Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah, USA Ajay Nahata Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah, USA

It is generally accepted that the terahertz (THz) dielectric properties of conventional metals are orders of magnitude larger than at optical frequencies. This is based on an extrapolation using the Drude model [1] and has led to the general view that metals can be approximated at perfect electrical conductors (PECs) in the long wavelength regime.However, the PEC approximation yields results that deviate from experimental results. For example, the predicted 1/e out-of-plane decay length for surface plasmon-polaritons (SPP) on unstructured metal films is on the order of ten cm based on the published dielectric data, while experimental measurements typically yield values on the order of a few mm [2].

Here, we show unambiguous measurements of the THz permittivity of several different conventional metals using a modified THz time-domain spectrometer, shown in Fig.1, that does not require a “perfect reference.”

We measure the complete time-domain electric field information at several different locations along the x axis and use that information to calculate the metal permittivity. Independently, we measure the 1/e decay lengths along both the x and z-axes and compare that to the values associated with the measured permittivity. In Fig.2, we show the 1/e propagation length along the x-axis for gold based on published dielectric data, from measured dielectric values and from direct measurements [3].

References

[1] M. A. Ordal, et.al., Appl. Opt. 22, 1099–1119 (1983).

[2] T.I. Jeon and D. Grischowsky, Appl.Phys.Lett. 88, 061113 (2006).

[3] S.Pandey, S.Liu, B.Gupta and A.Nahata, Photon. Res. 1,4, (2013).

ajay.nahata@utah.edu









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