Apodization pupils: design and performance (review)

Apodization applied to the pupil functions was widely used for the light field manipulation in the focal region of the optical focusing systems. Apodization pupils were divided into three categories by the structure type, i.e. slit, circular and complex pupil functions. For one-dimensional (slit type) apodization functions, the point spread function was obtained with suppressed sidelobes. The magnitude of reduction of the sidelobes was found to increased by the amplitude apodization across the slit function. For apodized circular pupil functions, the axial resolution of the optical systems was improved, and it was very helpful to improve the two-point resolution in the presence of optical aberrations such as defocus and spherical aberration. For complex apodized pupil functions, the full width at half maximum (FWHM) of the point spread function (PSF) was obtained less than that of the Airy PSF. The study proved that, within certain conditions, the complex apodizer was effective in removing the sidelobes from the aberrated impulse response (or PSF). In this review, a systematic study was performed in which the effect of aberrations and the complex apodization were used to improve the performance of the optical systems for resolving the two closely located point-sources under the incoherent, partially coherent and fully coherent light illumination. The concepts of the amplitude and phase diffractive optical elements were applied to reduce the size of the focal spot at tight focusing of differently polarized laser beams. This technique was also applied to increase the resolution beyond the diffraction limit for the composite image intensity distribution of the far-field objects formed by the incoherent optical system.