A method for the removal of a deposition on an optical element of an apparatus including the optical element includes providing an H2 containing gas in at least part of the apparatus includes producing hydrogen radicals from H2 from the H2 containing gas; and bringing the optical element with deposition into contact with at least part of the hydrogen radicals and removing at least part of the deposition. Further, a method for the protection of an optical element of an apparatus including the optical element includes providing a cap layer to the optical element by a deposition process; and during or after use of the apparatus, removing at least part of the cap layer from the optical element in a removal process as described above. The methods can be applied in a lithographic apparatus.