Ion beam figuring solution for high performance diamond optics

The outstanding physical properties of diamond make it the ultimate material for the efficacy of the CO2 lasers used to fuel the EUV light source.The efficacy of the laser is strongly influenced by the beam quality of the CO2 laser and depends strongly on the surface quality of the optical components used in the CO2 laser and beam delivery system. Achieving high flatness values on diamond exit windows is not trivial so new manufacturing processes are required. To achieve high flatness values on diamond, a new deterministic polishing method based on a reactive Ion beam process has been developed for CVD diamond substrates in close cooperation with Element Six, a leading company in synthetic diamond technology. Optical quality diamond wafers can be grown with sizes of up to 135mm diameter. When processed with ion beam figuring, flatness values of PV< λ/20 @ 632nm have been achieved reproducibly, values not realised on diamond surfaces before. For transmissive optics, TWF values of a few tenths of fringes @ 632nm have proven to be well within the capability of this new process technology as well. The development of a specific Ion source has ensured throughput times to better than those known from more traditional polishing techniques.