Elastic Emission Machining of Substrates for EUV, Optical, and Infrared Optics

The need for highly accurate and cost efficient deterministic polishing methods on a variety of materials is apparent. Diffraction limited, low cost, and low weight normal-incidence mirror systems are required to enablenbsp;telescopes for missions of all sizes, ranging from CubeSatsnbsp;to Probe and Flagship missions. Anbsp;solution that is applicable to any size and material is crucial. Elastic Emission Machiningnbsp;can achieve these tolerances and is scalablenbsp;while remaining highly precise with highly stable removal rates. EEM is a chemical polishing method which causes low-energy, non-damaging collisions to occur between particulates and the substrate surface. These gentle collisions do not directly remove material from the surface. Chemical reactions occur between the particulates and the surface whereby the particles become chemically bound to the surface atoms. The fluid in which the particles are immersed is accelerated to flow and produces a sheering force on the bound particle, which pulls the particle ndash; and its attached substrate atom ndash; from the substrate, thereby producing an atomic-level machining operation. This type of material removal process does not inject heat, nor does it damage the atomic lattice structure, preventing sub-surface damage. Due to the material being removed efficiently from the surface by the polishing particulate, a Beilby layer is not allowed to form and ldquo;healrdquo; over the optical surface. During the Phase I effort it wasnbsp;successfully demonstrated on Ultra Low Expansion Glass (ULE)nbsp;and Zerodur. Mirror support through mitigation on light-weighted ULE and Zerodur substrates was also a goal which OptiPro wished to complete in this Phase I project. Support print through is a problem with light-weighted mirrors in which the support structures are apparent in the mirror surface whichnbsp;EEM can address and solve. These factors were found to be successfully mitigated during the project and successful correction of light-weighted mirrors was accomplished.