We characterize phase and amplitude apodization induced when a converging beam passes through an evanescent gap. The apodization is caused by vector transmission and reflection properties. General characteristics are described for solid immersion lens indices from nSIL = 1.5 to 3.1, gap heights from h = 0 to 300 nm, and marginal ray angles αm = 0.7 or 0.84, where αm is the direction cosine of the marginal ray angle inside the solid immersion lens. A small amount of defocus is found to be a good compensator of the phase apodization for low nSIL and h. After proper defocus is applied, asymmetry of focus in the spot may remain, primarily due to the uncompensated amplitude apodization. Simplification of the phase and amplitude characteristics is accomplished by applying a Jones-matrix expansion to the transmission coefficient through the gap. Simulation and experiment quantify the effect with a simple solid immersion lens geometry.
- Evanescent coupling
- Near-field optics
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics