A source-collector device includes a target unit having a target surface of plasma-forming material and a laser unit to generate a beam of radiation directed onto the target surface to form a plasma from said plasma-forming material. A contaminant trap is provided to reduce propagation of particulate contaminants generated by the plasma. A radiation collector includes a one or more grazing-incidence reflectors arranged to collect radiation emitted by the plasma and form a beam therefrom, and a filter is configured to attenuate at least one wavelength range of the beam.