The impact of loss on plasmonic resonances in a slit in a real metal

There is a common misconception that a narrower slit leads to more enhancement but in the presence of loss, the narrowest slit does not give the highest field enhancement which is important for SERS and nonlinear optics applications. Here, the impact of loss on the plasmonic resonances in metal-insulator-metal slits is analyzed. The reflection of TM light in a subwavelength slit in a real metal has been calculated using mode matching theory and orthogonality principle of electric and magnetic field for a real metal exhibiting both dispersion and loss. Then the calculated reflection phase has been used to calculate plasmonic resonances. The impact of metal loss and the presented theory on plasmonic resonances is investigated. The theoretical calculations agree well with comprehensive simulations, but differ substantially from the conjugated orthogonality result, as was used in past analytical works, showing promise for simple theoretical investigation of future plasmonic MDM structures.