| abstract |
A polycrystalline chemical vapour deposited (CVD) diamond wafer comprising: a largest linear dimension equal to or greater than 125 mm; a thickness equal to or greater than 200 μm; and one or both of the following characteristics measured at room temperature (nominally 298 K) over at least a central area of the polycrystalline CVD diamond wafer, said central area being circular, centred on a central point of the polycrystalline CVD diamond wafer, and having a diameter of at least 70% of the largest linear dimension of the polycrystalline CVD diamond wafer: an absorption coefficient≦0.2 cm −1 at 10.6 μm; and a dielectric loss coefficient at 145 GHz, of tan δ≦2×10 −4 . |