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

Diffraction limited, low cost, and low weight mirror systems are required to enable and enhance telescopes for missions of all sizes, from CubeSats to Flagship missions. These missions also vary in their operating wavelengths from ultraviolet to far-infrared. With this wide range of sizes and operating wavelengths, a solution that is applicable to any size and material is necessary, capable of the following performance goals: Mid-spatial frequency errors (6 – 60 cycles per aperture (CPA)) <5nm RMS High-spatial frequency errors (>60 CPA) <1.5 nm RMS Micro-roughness <0.5nm RMS A methodology that OptiPro has recently employed can achieve these tolerances and is scalable for any size of optic: Elastic Emission Machining. EEM is a chemical polishing method, which causes low-energy collisions to occur between particulates and a substrate. These collisions cause chemical reactions whereby the particles become chemically 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 it – and its attached substrate atom – from the substrate, producing an atomic-level machining operation. This process does not damage the atomic lattice structure, allowing for no sub-surface damage. With the material being removed from the surface by the particulate, a Beilby layer is not allowed to form over the optical surface. This technology has been demonstrated on Silicon, and during this Phase I we will demonstrate the process on Ultra Low Expansion glass (Corning Incorporated) and Zerodur (Schott AG). The other aspect of this project which OptiPro will demonstrate is the mitigation of mirror support print through on light-weighted mirrors. Support print through is a problem with light-weighted mirrors where the support structures are apparent in the mirror surface, due to a few factors which we believe EEM could solve, with its highly stable removal rates and low force for polishing.

With the capability to manufacture ULE and Zerodur optical components to the diffraction limit, NASA will be able to ensure that their telescopes, CubeSats, and Flagship missions have highest opportunity for success, enabling and enhancing future systems. OptiPro’s Elastic Emission Machining Platform, with the success of this proposed SBIR project, will be capable of manufacturing any light-weighted optical component, made of Silicon, ULE or Zerodur, to the diffraction limit of their operating wavelength.

EEM has proven its capabilities on diffraction limited Silicon polished for use in the Department of Energy’s Synchrotron and Linear X-ray accelerators, which also use Zerodur and ULE in their beamline systems. Extreme Ultraviolet Lithography systems also use Zerodur and ULE in their systems and with the ever-growing need for microchips, more efficient and accurate optics are needed.

This is early/mid-stage (TRL 5) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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