Fabrication of CVD Diamond Optics with Antireflective Surface Structures

Polycrystalline CVD diamond is an excellent material for advanced optical applications, especially in the IR spectral range. However, one drawback of diamond is the significant reflection loss of 29%, caused by its high refraction 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 by the substrate removal to obtain the patterned diamond replica. An increase in IR transmission up to T = 80% was observed at wavelengths λ > 10 μm 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 transmission could be achieved by combining ARS and a single layer AR coating of amorphous carbon.