Fabrication of CVD diamond optics with antireflective surface structures

Polycrystalline CVD diamond is an excellent material for advanced optical a pplications, especially in the IR spectral range. However, one drawback of diamond is the significant reflection loss of 29%, caused by its high refra ction index n = 2.4. We fabricated subwavelength, "moth-eye" antireflective structured (ARS) surfaces (two-dimensional array of pyramids) by filling, with CVD diamond the inverted pyramids etched in a Si substrate, followed b y the substrate removal to obtain the patterned diamond replica. An increas e in IR transmission up to T = 80% was observed at wavelengths lambda > 10 mu m for the ARS surfaces compared to T = 71% for flat surfaces even at the non-optimized geometry of the surface relief. A further increase in transm ission could be achieved by combining ARS and a single layer AR coating of amorphous carbon.