System and method for simulating an aerial image

Simulated aerial images for an optical system are made by forming a reference aerial image of a first mask used in connection with the optical system, and then capturing and processing the reference aerial image to generate a set of expansion functions representative of the optical system. The expansion functions account for aberrations and misalignment of the optical system, as well as any aberrations or other defects of a camera therein. The expansion functions are then used to compute simulated aerial images of other masks projected by the optical system. Thus, the expansion functions implicitly represent a calibration of the optical system for purposes of aerial image simulation, obviating the need for direct measurement of the actual aberrations and misalignment. Hence, a simulated aerial image of a second mask for the optical system can be computed by applying the expansion functions to a design of the second mask.