The properties of tight dark focal spot created using a simple circular π phase plate are presented. For focusing elements with low numerical aperture, the focal plane intensity has r4 dependence, while for focusing elements with high numerical aperture, vectorial diffraction effects become important, and the focal plane intensity surprisingly approaches r2 dependence, indicating a much tighter dark spot.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry
- Electrical and Electronic Engineering