Rapid, Nonmechanical, Damage-Free Figuring Of Optical Surfaces Using Plasma-Assisted Chemical Etching (PACE): Part I Experimental Results

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Abstract
We present experimental results of an ongoing investigation demonstrating that Plasma Assisted Chemical Etching (PACE) can rapidly and controllably figure and smooth optical surfaces without mechanical contact; thus, removing the constraints on the design of optical elements imposed by mechanical processes, and, allowing higher quality optical surfaces. This process employs a plasma etch process originally developed to pattern micro-electronic circuits by etching through a relatively non-erodable lithographically patterned mask. The PACE process shapes the optical surface by removing material in a small area under a confined reactive gas plasma moved over the surface. Rates of removal as high as 10 m per minute are obtainable with accurate control. The removal footprint can be varied during the process. PACE inherently smooths or polishes while removing material, exposing a virgin surface free of process generated contamination and subsurface damage. Although other materials can also be figured by a PACE process, for this study, apparatus and processes were developed to explore the figuring of fused silica. Results will be shown demonstrating: repeatability and control of removal rate and footprint; predictability of material removal with plasma "tool" motion; and smoothing.

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