1. An apparatus for increasing a process window associated with imaging a mask design onto a target portion of a substrate, said apparatus comprising: a computer system configured to optimize polarization and intensity at each of a plurality of points of an illuminator used to illuminate the mask design by performing the steps of: (a) determining an illumination intensity for at least one point on the illuminator for at least two polarization states; (b) determining image log slope (ILS) for the at least one point on the illuminator for the at least two polarization states; (c) determining a maximum image point where the ILS is at least near zero for the at least one point on the illuminator; (d) selecting an optimal polarization state corresponding to the maximum ILS for the at least one point on the illuminator; and (e) repeating steps (a)-(d) for each of the plurality of points on the illuminator.