Coherent imaging of periodic thick fine isolated structures

The diffraction orders and coherent bright and dark field images produced by isolated steps and grooves (notches and trenches) are examined. The isolated structures are approximated by means of a grating with a
large period that contains small, widely separated, lamellar structures. The rigorous modal method for TE polarized incident light is used for the numerical calculations. Structures in two types of dielectric material, refractive index n = 1.5 and n = 4.0, are discussed. The images are examined for variations with several parameters, including width and thickness of the structure and focus position. Several approximate methods for calculating these images, based on first-order approximations, are suggested.