Coupling between surface plasmons and nonresonant transmission in subwavelength holes at terahertz frequencies

Transmission spectra of terahertz pulses through periodic array of subwavelength holes exhibit a characteristic evolution with various hole widths. The peak absolute transmittance approaches a maximum value at a critical hole width, while linewidth broadening and blueshift of peak frequency are observed with increasing hole width. Such characteristic evolution is attributed to the coupling between discrete resonant excitation of surface plasmons and continuum nonresonant transmission through the holes; this agrees well with the numerical analysis based on the Fano model and the measured angle-resolved transmission band structures.