An optical arrangement, in particular in a projection exposure apparatus for EUV lithography. In an aspect an optical arrangement has a housing (100, 200, 550, 780) in which at least one optical element is arranged, and at least one subhousing (140, 240, 560, 790, 811, 823, 824, 831, 841) which is arranged within the housing and which surrounds at least one beam incident on the optical element in operation of the optical system, wherein the internal space of the subhousing is in communication with the external space of the subhousing by way of at least one opening, wherein provided in the region of the opening is at least one flow guide portion which deflects a flushing gas flow passing through the opening from the internal space to the external space of the subhousing, at least once in its direction.