This work examines aspects of source mask polarization optimization (SMPO). Cases are described where unusual polarization conditions, beyond the familiar and expected XY or TE, are beneficial. These results are best understood by examining the diffraction patterns and noticing that image formation is influenced by interference between higher diffraction orders when the zeroth order is relatively weak. Examples include hole patterns with attenuated phase shift masks and also dark field illumination. Further analysis shows, however, that for some problems, perhaps most, aggressive mask optimization can transform the imaging problem in such a way that zeroth order light again dominates. Under these conditions familiar two beam imaging can be obtained with off-axis illumination, and then TE polarization will probably provide the best solution. From a computational point-of-view SMPO procedures are hampered by the fact that polarization affects the required optical proximity correction (OPC), the OPC affects the diffraction pattern, and the diffraction pattern and polarized source light interact to determine lithographic performance. This makes co-optimization of source, mask, and polarization conditions difficult, and a useful intermediate approach was found to be source mask optimization with a scalar imaging calculation.