Lithographic apparatus, beam delivery systems, prisms and device manufacturing method

A beam directing element configured to receive a substantially collimated input beam of predetermined wavelength propagating in a first direction and to output a substantially collimated output beam in a second direction includes a prism formed of a transparent material and having input and output faces, wherein the internal angle between the input face and the output face is such that when the input beam is incident on the input face substantially at Brewster's angle, it is internally incident on the output face at Brewster's angle. The beam directing element is useful in lithography, for example in beam delivery systems.