Designing surface plasmon resonance of subwavelength hole arrays by studying absorption

The surface plasmon (SP) resonance excited at subwavelength cylindrical hole arrays milled in metal films is systematically studied by solving the three-dimensional Maxwell's equations using the finite element method. The absorption spectrum of the hole arrays, combined with the electric-field distribution, is employed to investigate the plasmon resonance of the patterned metal film. It is found that (i) an SP resonance correlates to a resonant peak in the absorption spectrum, but not all the peaks in the spectrum correlates to the plasmon resonances; (ii) the size variation of the hole array will shift the resonant wavelength, i.e., an increment of 100 nm in the pitch p, the hole diameter d, and the hole depth t leads to a redshift of 60–70, 30–40, or 10–20 nm in the resonant wavelength, respectively; (iii) the maximum enhancement of the electric field on the surface of the metal film corresponds to the highest absorption peak, which can be achieved by designing the p, d, and t of the hole array; and (iv) for small holes (e.g., d=125 nm) or shallow holes (e.g., t=100 nm), the absorption characteristics of the hole arrays are particularly important as some resonant peaks are missing in their transmission spectra. Our finding is of particular importance in applications such as SP resonance based sensing.