A device having a waveguide formed of a continuous body of material that is transparent to radiation that passes through the waveguide, wherein the body has an input surface and an output surface, and a cooler configured to cool the input surface and/or the output surface. An exposure apparatus having a programmable patterning device that comprises a plurality of radiation emitters, configured to provide a plurality of radiation beams; and a projection system, comprising a stationary part and a moving part, configured to project the plurality of radiation beams onto locations on a target that are selected based on a pattern, wherein at least one of the radiation emitters comprises a waveguide configured to output a radiation beam that comprises unpolarized and/or circularly polarized radiation.