Fabry-Perot effects in THz time-domain spectroscopy of plasmonic band-gap structures

Using terahertz time-domain spectroscopy, we study transmission in one-dimensional arrays of slits fabricated on metal plates by laser machining. The enhanced peaks of zero-order transmission spectra are attributed to the combined effects of Fabry-Perot and surface plasmon resonances. Angle dependence of transmission spectra shows that the strongly surface plasmon-enhanced peaks appear when the Fabry-Perot-type resonance is located nearby in energy. This means that surface waves traveling in the horizontal direction couple with nearest Fabry-Perot resonance to generate enhanced peaks. These results are in excellent agreement with theoretical calculations.