A poly crystalline chemical vapour deposited (CVD) diamond wafer comprising: —a diameter >40 mm; —a thickness >1.0 mm; —an absorption coefficient ≤0.1 cm−1 at 10.6 μm; and ⋅a micro feature density, especially in the form of “black spots”, meeting the following specification: —in a central area of the polycrystalline CVD diamond wafer from 0 to 20 mm radius there are no more than 100 micro features of a size between 0.002 and 0.008 mm2, no more than 50 micro features of a size between 0.008 and 0.018 mm2, no more than 25 microfeatures of a size between 0.018 and 0.05 mm2, and zero microfeatures of a size between 0.05 and 0.1 mm2, and ⋅in an outer region of the polycrystalline CVD diamond wafer from 20 to 40 mm radius there are no more than 200 microfeatures 2 of a size between 0.002 and 0.008 mm2, no more than 150 microfeatures of a size between 0.008 and 0.018 mm2, no more than 100 microfeatures of a size between 0.018 and 0.05 mm2, and zero microfeatures of a size between 0.05 and 0.1 mm2.