Near-field properties of double nanoslits coupled with a wide collection cavity drilled on a metal film

The transmission and interference characteristics of light through slit-doublet structure milled in a metal film are significantly changed by introducing a wide collection cavity. We investigate them by the finite-difference time-domain method. Two types of interference patterns on the output surface, i.e., the periodic single peak or the periodic double peaks profile, are observed by varying the thickness of the double slits. It is also found that the peak value of the near-field interference fringes can be enhanced nearly two times that in normal slit-doublet structure (without the wide collection cavity). The physical mechanism is explained in detail.