SYNTHETIC DIAMOND OPTICAL ELEMENTS

An optical element 10 is made of synthetic diamond material and has an anti-reflective surface pattern 16 formed directly in at least one surface. The optical element has an absorption coefficient measured at room temperature of ≤ 0.5 cm-1 at a wavelength of 10.6 µm. It has a reflectance at said at least one surface of no more than 2% at an operating wavelength of the optical element. It has a laser induced damage threshold which 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/or is at least 1 MW/cm2 measured using a continuous wave laser at a wavelength of 10.6 µm. The surface pattern may be formed by an inductively coupled plasma (ICP) etching process which minimises nitrogen-vacancy (NV) defects in single crystal chemical vapour deposition (CVD) diamond materials.