Fabrication of optical elements with better than λ/1000 thickness uniformity by thin-film deposition through a multi-aperture mask

A technique is presented for sub-nanometre correction of precision-polished optical surfaces. The technique uses thin metallic masks with multiple apertures of varying widths to selectively occlude a beam of depositing species in an ion beam sputtering system. The masks are designed directly from measured surface profile maps of the optical surface, and are fabricated using well-established laser-cutting technology commonly used to fabricate solder masks for the semiconductor industry. The selective deposition has proved highly effective for fabrication of large-aperture Fabry-Perot filters and has resulted in optical uniformities of less then 0.3 nm rms over a clear aperture of 37.5 mm. This manuscript will give details of the mask design, deposition technique, and results from recent surface correction runs.