THz time-domain quasi-optical systems for characterization of frequency selective surfaces

Miguel Camacho, Suzanna Freer, Rafael R Boix, Sergei A. Kuznetsov, Miguel Beruete, Miguel Navarro-Cia

Research output: Contribution to conference (unpublished)Abstractpeer-review


At the expense of frequency resolution, time-domain spectrometers provide access to the frequency range 0.2 to 3 THz in a continuous fashion, unlike vector network analysers that enable a banded solution up to 1.1 THz [1]. This broadband response can be exploited to obtain the performance of frequency selective surfaces at the design frequency and harmonics in an effortless way. However, time-domain spectrometers rely on quasi-optical systems (usually based on a set of focusing and collimating lenses) that may induce artifacts in the measurements [2].
To illustrate the impact that the quasi-optical setup can have in the measured performance of frequency selective surfaces, we investigate with the TERA K15 all fibre-coupled THz spectrometer from Menlo Systems truncated subwavelength hole arrays displaying the so-called extraordinary transmission [3]. Three different setups are used to study the scattering from truncated subwavelength hole arrays under two different illumination conditions (collimated and focused beam illumination): (i) collimated beam illumination - setup 1 has no lenses before and after the sample; (ii) focused beam illumination - setup 2 has a focusing lens before the sample, whereas setup 3 has a focusing and a collimated lens before and after the sample, respectively. The distance between the detector unit and the sample is approximately 110 mm. For the measurements, the lock-in constant is set to 300 ms and the total temporal length of the recorded waveforms is at least 208 ps to have a spectral resolution of 4.8 GHz in the worst case. An efficient implementation of the Method of Moments [4] enable us to model the measurements in a fraction of the time that would take us with a full-wave electromagnetic simulation using the commercial software CST Microwave Studio.
Although the extraordinary transmission peak is observed with all setups, its amplitude depends strongly on the quasi-optics (i.e. setup) as well as on the number of holes. This strong dependence is linked to the optics and the leaky-wave mechanism mediating in the extraordinary transmission phenomenon. The scattering measurements demonstrate the appearance of a grating lobe above the extraordinary transmission frequency that is associated to the m = -2 space harmonics entering in the radiation region. Our results reveal that, although setup 3 is the preferred configuration for spectroscopy applications, it is the one with the most negative effect on the measurements of extraordinary transmission surfaces.

[1] M. Naftaly, Terahertz Metrology. Boston: Artech House, 2015.
[2] M. Navarro-Cía, V. Pacheco-Peña, S. A. Kuznetsov, and M. Beruete, “Extraordinary THz Transmission with a Small Beam Spot: The Leaky Wave Mechanism,” Advanced Optical Materials, vol. 6 (8), p. 1701312, Apr. 2018.
[3] T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature, vol. 391(6668), 667–669, Feb. 1998.
[4] M. Camacho, R. R. Boix, and F. Medina, “Computationally efficient analysis of extraordinary optical transmission through infinite and truncated subwavelength hole arrays,” Physical Review E, vol. 93 (6), p. 063312, Jun. 2016.
Original languageEnglish
Publication statusPublished - Mar 2019
EventIET Colloquium on Millimetre-Wave and Terahertz Engineering & Technology 2019 - IET London: Savoy Place, London, United Kingdom
Duration: 15 Mar 201915 Mar 2019


ConferenceIET Colloquium on Millimetre-Wave and Terahertz Engineering & Technology 2019
Country/TerritoryUnited Kingdom


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