SCALAR AND ELECTROMAGNETIC DIFFRACTION POINT-SPREAD FUNCTIONS FOR HIGH-NA MICROLENSES

Scalar diffraction theories are often used to characterize optical ima ging systems in terms of their scalar diffraction point-spread functio ns (PSFs). This works well at large f-numbers (low numerical apertures (NA)), since polarization effects can then be ignored. But as the f-n umber decreases, polarization effects become more important and a full y vectorial diffraction theory is required to determine the electromag netic diffraction PSF of the system. In this paper we study a variety of low f-number refractive microlenses and characterize each in terms of its scalar as well as its electromagnetic diffraction PSF using the combined method of raytracing and diffraction (CMRD). We find that a polynomial aspherical surface gives less spherical aberration than a s pherical or ellipsoidal surface. For the polynomial surface both the s calar and the electromagnetic PSFs are found to be asymmetric about th e focal plane and to give focal shifts due to high-order spherical abe rrations. The differences between scalar and electromagnetic diffracti on PSFs are found to be small on the axis, due to symmetry, but for an f-number of 0.39, differences of up to 5% are found off-axis.