Apparatus and methods are used for controlling electromagnetic radiation pulse duration in a lithographic apparatus. A dividing element is arranged to divide an electromagnetic radiation pulse into a first portion and a second portion. A prism receives, refracts, and subsequently emits the first portion of the electromagnetic radiation pulse. A directing element is arranged to direct the first and second portions of the electromagnetic radiation pulse parallel to a common optical axis. The first portion combines with the second portion to form a combined radiation beam pulse. The combined radiation beam pulse has a longer pulse duration than the divided electromagnetic pulse and experiences no corresponding loss in intensity.