surface the surfaces of which are also parallel to the top 2 and bottom 3 of the mirror b as depicted in fig3 and 4 these cooler layers 11 are structured i e provided with a plurality of openings 11 u2032 and 11 u2033 and material stays surrounding these openings in such a way they form two chambers 12 and 13 for the inlet and outlet of a preferably liquid coolant for example water and between these chambers a cooling area 14 with a finely structured network of passageways formed by the openings 11 for the coolant which paths continuously branch out in all three perpendicular spatial axes so that the coolant flows through this cooling area 14 being constantly diverted in all three spatial axes thus producing an intensive cooling effect furthermore the cooler layers 11 are structured in such a way that continuous posts 15 made of copper are formed from the structuring or sections of the material stays surrounding the openings 11 u2032 in the connecting cooler layers the longitudinal sides of which posts are perpendicular to the levels of the layers of the mirror 1 and as the remaining wing like sections of the structured cooler layers 11 protruding from these posts 15 are also subjected to the intensive flow of coolant the posts 15 are.