Synthetic diamond optical elements

An optical element comprising: synthetic diamond material; and an anti-reflective surface pattern formed directly in at least one surface of the synthetic diamond material, wherein the optical element has an absorption coefficient measured at room temperature of ≤0.5 cm−1 at a wavelength of 10.6 μm, wherein the optical element has a reflectance at said at least one surface of no more than 2% at an operating wavelength of the optical element, and wherein the optical element has a laser induced damage threshold meeting one or both of the following characteristics: the laser induced damage threshold is at least 30 Jcm−2 measured using a pulsed laser at a wavelength of 10.6 μm with a pulse duration of 100 ns and a pulse repetition frequency in a range 1 to 10 Hz; and the laser induced damage threshold is at least 1 MW/cm2 measured using a continuous wave laser at a wavelength of 10.6 μm.