Damage area as a function of fluence. (a) Experimental measurements taken at 18 fluence levels, each repeated three times; scatter bars indicate variability in the damage area. Three regions are separated by dashed lines: Zone I, where no damage is observed (example at 0.07 J/cm²); Zone II, where apparent coating damage occurs but is not counted (example at 0.09 J/cm²); and Zone III, where missing micromirrors define the quantified damage area (examples at 0.11, 0.12, and 0.18 J/cm²). Damage characterisation uses (b) confocal z-stacks of 40 images with 1-μm steps and (c) bright-field microscopy.