An EUV light source is disclosed which may comprise at least one optical element having a surface, such as a multi-layer collector mirror; a laser source generating a laser beam; and a source material irradiated by the laser beam to form a plasma and emit EUV light. In one aspect, the source material may consist essentially of a tin compound and may generate tin debris by plasma formation which deposits on the optical element and, in addition, the tin compound may include an element that is effective in etching deposited tin from the optical element surface. Tin compounds may include SnBr4, SnBr2 and SnH4. In another aspect, an EUV light source may comprise a molten source material irradiated by a laser beam to form a plasma and emit EUV light, the source material comprising tin and at least one other metal, for example tin with Gallium and / or Indium.