An optical integrator having a first surface and a second surface that is used in a lithographic apparatus to modify light. The first surface is reflective, defines a volume, and is configured to be disposed in an optical illumination system along an optical axis, to surround the optical axis, and to reflect a light along a path incident upon the first surface. The second surface is disposed in the volume and has a first section of the second surface that is semi-reflective and is configured to reflect a first portion of a light along a path incident upon the first section of the second surface and to transmit a second portion of the light along the path incident upon the first section of the second surface. The second surface increases the number of reflections of the light to increase the uniformity of the intensity distribution of the light.