Resolution Enhancement in High Numerical Aperture Optical System

Resolution enhancement requirement occurs in many optical systems, such as in imaging system, optical microscopy domain, optical lithography, and optical data storage. Some enhancement techniques are proposed, including higher numerical aperture (NA) and ring illumination. In this article, the resolution enhancement in high numerical aperture optical system is investigated by vector optics theory. It was found that the vector characteristics of the incident beam in high numerical aperture optical system affects resolution enhancement effect remarkably, and may weaken resolution enhancement effect for some cases, namely, the focus does not always decrease with increasing numerical aperture, in addition, the full width half maximum (FWHM) of focal spot differs for different direction for high numerical aperture and ring illumination, which means the resolution enhancement effect differs in different direction. Therefore, resolution enhancement of higher NA and ring illumination should be taken care of in practice use.