Optical assembly with suppression of degradation

Optical assembly, comprising:

• a beam generating system generating radiation at an operating wavelength (λb)
• at least one optical element arranged in a residual gas atmosphere and subjected to the radiation, which induces a degradation of a surface of the optical element, and
• a feed device feeding at least one gaseous constituent into the residual gas atmosphere to suppress the degradation of the surface of the optical element that is induced by the radiation, wherein either:
• (i) a beam diameter (d) of the radiation at a surface of the optical element lies above a threshold value (dc), thereby suppressing the degradation by the gaseous constituent, or
• (ii) the beam diameter (d) at the surface of the optical element lies below the threshold value (dc), so that effectiveness of the suppression of the degradation is reduced, and a further device enhancing suppression of the degradation of the surface is assigned to the optical element, and wherein the threshold value (dc) is between 1 mm and 0.1 mm.