Figure 4.

The edge of the nested mirror must be shaped to an ellipse to avoid lost rays at the corner. However, even a straight-line approximation is not too bad. For example, for the prototype mirrors the maximum missing mirror surface is about 5 µm wide and the total area lost is about 1.3 × 10⁵ µm². This will cost about 6.5% for a 100 µm × 100 µm incident beam. If the edge is profiled to a simple cylinder and tilted slightly (∼15 µrad), the missing mirror area is reduced to 0.5% of the total mirror surface used.