Patent ID: 8890099

Claim:
A radiation source having a fuel droplet generator configured to provide a stream of droplets of fuel at least one laser configured to vaporize at least some of said droplets of fuel, whereby radiation is generated, the fuel droplet generator comprising: a nozzle; a fuel feed line; a reservoir; a pumping device configured to supply a flow of molten metal fuel from the reservoir through the fuel feed line and out of the nozzle as a stream of droplets; and a replaceable filter assembly in the fuel feed line and configured to filter said molten metal fuel in use, the replaceable filter assembly having a rigid support plate having first and second opposed faces, with one or more channels, each extending from a respective first aperture in the first face through a respective second aperture in the second face, and supporting a filter membrane on the first face and extending over each first aperture of the first face, wherein the filter membrane comprises mutually spaced holes therein, with each first aperture aligned with a plurality of the holes to provide fluid connection between the plurality of holes and the respective channel.