US Patent 10407770 Large area optical quality synthetic polycrystalline diamond window

A polycrystalline chemical vapor 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; andone 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, centered 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; anda dielectric loss coefficient at 145 GHz, of tan δ≤2×10−4.