Extraordinary Mid-Infrared Transmission of Subwavelength Holes in Gold Films

Gold (Au) nanoholes are fabricated with electron-beam lithography and used for the investigation of extraordinary transmission in mid-infrared regime. Transmission properties of the nanoholes are studied as the dependence on hole-size. Transmittance spectra are characterized by Fourier transform infrared spectroscopy (FTIR) and enhanced transmittance through the subwavelength holes is observed. The transmission spectra exhibit well-defined maximum and minimum of which the position are determined by the lattice of the hole array. The hole-size primarily influence the transmission intensity and bandwidth of the resonance peak. With an increase of hole-size, while keep lattice constant fixed, the intensity of the resonance peak and the bandwidth increases, which are due to the localized surface plasmons. Numerical simulation for the transmission through the subwavelength holes is performed and the simulated results agree with the experimental observations.