This disclosure relates to lithography using pulsed laser illumination. In particular it relates to lithography for producing electronic devices on wafers using multi-mode excimer and molecular lasers, e.g. KrF, ArF, and F2 lasers. It may also apply to illumination systems where several single-mode sources are mixed or one single-mode laser beam is split and recombined with time delays, thereby creating an equivalent multimode source and to EUV lithography. Particular aspects of the present invention are described in the claims, specification and drawings.