Wavelength scale terahertz spectrometer based on extraordinary transmission

Subwavelength-slotted parallel plate waveguides exhibit a localized electromagnetic resonance bound to the slits at a frequency slightly below the transverse electric cutoff [R. Merlin, Phys. Rev. X 2, 031015 (2012)]. The resonance is long-lived and, as opposed to the vanishingly small transmission shown by a single sub-wavelength aperture, it gives perfect transmission for perfectly conducting plates. We show that the aperture-supported resonances of a pair of slotted copper plates have long lifetimes at Terahertz (THz) frequencies. Finite element method calculations show that these bound resonances can have quality factors greater than 100. The effects of the plate dimensions and imperfect parallel alignment are also discussed. Using THz time domain spectroscopy, we measured the transmission of a broadband pulse through a test structure for several plate separations and demonstrated, as a proof-of-principle, the function of the slotted waveguide as a highly compact THz spectrometer.

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