Hybrid Fabrication of Large, Low-Scatter Diffractive Optics

We propose a new approach to the fabrication of large, low scatter diffractive optics using a hybrid of existing ¿off-the-shelf¿ methods. Although several techniques are used to make diffractive optics, no single method is currently capable of the large clear aperture size, wavefront accuracy and surface quality that our proposed hybrid method offers. Using existing tools, an accurate DOE pattern is transferred to the final substrate through three proprietary steps, successively removing surface roughness and edge errors with each step. Our approach will allow the fabrication of large (greater than 1 meter), lightweight, low cost diffractive optics on both planar and curved surfaces for NASA applications. The resulting surface smoothness and flatness should be as good or better than is found on refractive optics made by traditional polishing processes, with a wavefront perfection only found with diffractive optics. These devices can fulfill advanced imaging and light gathering missions never before attempted using off-the-shelf fabrication methods, and materials that cannot be diamond turned. The proposed method can also be used in the fabrication of plane and powered gratings and multilevel sub-wavelength structures.