The invention relates to a method for in situ protection of a surface (7a) of an aluminum layer (7) of a coating (6) – which reflects VUV radiation (11, 21) – of an optical element (4), which is arranged in an interior of an optical arrangement for the VUV wavelength range, against the growth of an aluminum oxide layer (8), comprising: carrying out an atomic layer etching process for layer-by-layer removal of the aluminum oxide layer (8), wherein the atomic layer etching process comprises a surface modification step and a material detachment step, wherein, in the surface modification step, at least one boron halide as surface-modifying reactant is fed to the interior in a pulsed manner, and wherein a plasma (31) is generated in the interior at a surface (8a) of the aluminum oxide layer (8) at least during the material detachment step. The atomic layer etching process is carried out until the aluminum oxide layer (8) attains a thickness (D) of less than 5 nm or the aluminum oxide layer (8) is kept at a thickness (D) of less than 5 nm by the atomic layer etching process. The invention also relates to an optical arrangement for the VUV wavelength range, for example an inspection system or a VUV lithography apparatus.
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