11 November 1999 LIGO optics manufacture: figuring transmission core optics for best performance
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Abstract
The Laser Interferometer Gravitational-wave Observatory (LIGO) is a long baseline Michelson interferometer, with arms of up to 4 km in length each containing a Fabry Perot cavity. CSIRO has manufactured 32 core optical components for the LIGO interferometer consisting of five different groups of optical elements. Long radii of curvature (7 km - 15 km) and tolerances in the order of plus or minus 200 m in the radius are specified. Although the components are made of hyper pure fused silica there are some residual inhomogeneities in the material. The optics used in transmission must be figured so that the influence of these material inhomogeneities on the transmitted wave front is compensated for. This was done by correcting the surface figure on side 2 of the optics. The approach we took to manufacturing the transmission optics was to calculate the quadratic component of refractive index gradient (Delta) n of the substrate from the measurements of the transmitted wavefront and the surface profile of the two substrate surfaces, determine what shape had to be produced on side two of the substrates to compensate for this gradient and then produce this by optical polishing. The surfaces were polished on rigid solid laps of Zerodur coated with a thin layer of Teflon as the polishing matrix, a technique developed by CSIRO for super-polishing very flat surfaces.
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Achim J. Leistner, Achim J. Leistner, David I. Farrant, David I. Farrant, Bozenko F. Oreb, Bozenko F. Oreb, Edita Pavlovic, Edita Pavlovic, Jeffrey A. Seckold, Jeffrey A. Seckold, Christopher J. Walsh, Christopher J. Walsh, } "LIGO optics manufacture: figuring transmission core optics for best performance", Proc. SPIE 3782, Optical Manufacturing and Testing III, (11 November 1999); doi: 10.1117/12.369188; https://doi.org/10.1117/12.369188
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