Enhanced zero-order transmission of terahertz radiation pulses through very deep metallic gratings with subwavelength slits

Very deep metallic grating structures with subwavelength slits are processed to study the transmission properties of terahertz radiation pulses. The experiments have been performed with two samples. The delay of the terahertz pulses and the corresponding enhanced unresonant transmission spectra through the samples are observed. A simple interpretation is presented based on the combination of zero-order diffraction of the gratings with the coupling of the surface plasmon polaritons formed on the top and bottom of the gratings. The experimental results are in good agreement with theoretical calculations.