Non-paraxial focusing by microlenses under arbitrary spatial coherence

Abstract

Non-paraxial focusing of monochromatic optical fields under arbitrary spatial coherence by spherical microlenses is theoretically discussed and numerically analyzed. A 3D concentration of the power spectrum determines the focal volume, which has rotation symmetry around the optical axis and whose maximum is corresponding to the focal point. A quantitative descriptor is introduced for characterizing the focal volume under different conditions, such as transverse illumination area on the lens, focal depth, radii of the spherical surfaces and spatial coherence of the illumination.