The wave-front spacing in the focal region of an aplanatic focusing system is investigated by use of the vectortheory of electromagnetic diffraction for monochromatic, linearly polarized incident light. It is shown that, insystems of high numerical aperture, the wave-front spacing near the focus is significantly larger than the wavelength of the incident light and that the wave-front spacing changes significantly within a few wavelengths of the focus and can be less than a wavelength.
展开▼
