  Surface plasmon resonance in super-period metal nanoslits can be observed in
the first order diffraction as well in the zeroth order transmission. In this
paper, surface plasmon resonance modes in various super-period gold nanoslit
arrays are investigated. It is found that the surface plasmon resonance
frequencies are determined by the small period of the nanoslits in super-period
nanoslits. The number of nanoslits in the unit cell super-period and the
nanoslit width do not control the surface plasmon resonance frequencies. It is
also found that the resonance wavelength observed in the first order
diffraction reveals more accurate the real surface plasmon resonance wavelength
in the metal super-period nanoslit array device.
