Differential numerical aperture methods and device

1. Field of the Invention (Technical Field) Devices and methods for differential numerical aperture analysis of samples, utilizing angle-of-incidence measurements resulting from variable illumination or observation numerical apertures, or both. Metrology applications are provided, and more particularly including scatterometer, ellipsometer and similar analysis methods, including bi-directional reflectance or transmission distribution function measurement. The provided devices and methods enable analysis of critical dimensions of samples utilizing a minimum of moving parts, with the range of striking or scattering angles varied by a variable numerical aperture or apertures.