Due to diffraction light cannot be focused to a spot smaller than about half its wavelength in the far-field using conventional optics. This poses an obstacle for several practical engineering problems, notably nanolithography. Confining light with an aperture is a straightforward way to generate a sub diffraction-limited spot. Understanding the physics of the apertures provides insight into the design and modeling. This work is based on resonant ridge apertures, particularly bowtie apertures. This geometry provides high transmission while maintaining very good light confinement.

The motivation for this work is direct-write nanolithography, although the tools presented have widespread applications. To this end we study nanoscale apertures, identify their transmission characteristics including resonances, and provide the insight necessary for their design. Nanoscale apertures can be used to define patterns by moving them relative to a photoresist. We describe the work leading to a system capable of writing multiple lines in parallel. The quality of the patterns is highly dependent of their fabrication. In this work we use Focused Ion Beam (FIB) milling, the limitations of which are discussed. Understanding and optimizing this procedure is important for successfully fabricating the apertures as well as modeling their performance.

Based on the study of the bowtie aperture we show how to enhance its transmission by adding a grating structure to the mask. This is demonstrated experimentally. We also show how a resonant aperture can couple to waveguides which may have photonic applications. We also investigate what happens when the apertures are placed in an array, demonstrating that the transmission can exceed the light incident on the open area by a factor of four in the infrared. This has frequency selective surface applications as well as potential as a sensor. We also show how the aperture array can be designed to trap light in a weakly absorbing layer. Finally we design a bowtie aperture array to enhance the efficiency of thin film silicon solar cells up to 39%.