Nanofocusing via Efficient Excitation Surface Plasmon Polaritons in a Hollow Aluminum Wedge

Efficient nanofocusing down to a few nanometers in a hollow aluminum wedge is numerically investigated. The waveguide propagation modes are efficiently converted to internal surface plasmon polaritons via a pair of grooves fabricated at the inner surface of the wedge and a remarkable field enhancement is realized at the aperture. The excitation efficiency can be further improved by optimizing spatial wavefront modulation of the incident light field via a binary optical element, and the output intensity through a 5-nm aperture is enhanced by 786 times compared with a conventional 100-nm aperture hollow metallic wedge.