27 December 2001 Wet-etch figuring: optical surfacing by controlled application of etchant solution using the Marangoni effect
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Abstract
Wet-etch figuring (WEF), a computer-controlled method for generating arbitrarily shaped optical surfaces using wet chemical etching, has been developed. This method uses applicator geometry and surface tension gradients (the Marangoni Effect) to define and confine the footprint of a wetted etchant zone on the surface. Capillary forces attach the flowing etchant solution to the underside of the optic being figured. No mechanical or thermal stresses or residues are applied to the optic by this process. This enables interferometric measurement of the glass thickness while surfacing, which then controls the placement and dwell time of the wetted zone. The result is a truly deterministic, closed-loop figuring process with a high degree of optical precision. This process can figure submillimeter thickness, large-aperture plates or sheets that are very difficult to finish by conventional methods. Automated linear and circular spot etching tools were used to demonstrate surfacing on 380 micron-thick glass sheets, to Strehl better than 0.8, as specified by data array or Zernike polynomials.
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Michael C. Rushford, Jerald A. Britten, Curly R. Hoaglan, Ian M. Thomas, Leslie J. Summers, Sham N. Dixit, "Wet-etch figuring: optical surfacing by controlled application of etchant solution using the Marangoni effect", Proc. SPIE 4451, Optical Manufacturing and Testing IV, (27 December 2001); doi: 10.1117/12.453623; https://doi.org/10.1117/12.453623
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