OPTICAL ASSEMBLY WITH SUPPRESSION OF DEGRADATION

摘要

An optical assembly including: a beam generating system generating radiation (6) at an operating wavelength, an optical element (13, 14) arranged in a residual gas atmosphere (16) 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. Either a beam diameter (d) of the radiation at the surface of the optical element, lies above a threshold value (dc), thereby suppressing the degradation by the gaseous constituent, or, if the beam diameter (d) at the surface (14a) of the optical element (14) lies below the threshold value (dc) so that the effectiveness of the suppression of the degradation is reduced, at least one further device (25, 27) enhancing suppression of the degradation of the surface (14a) is assigned to the optical element (14).

主权项

1. 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.