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The MicroFinish Topographer and the Solar Telescope

The MicroFinish Topographer helped bring you this spectacular image of the sun.

The smoothness criterion on the Daniel K. Inouye Solar Telescope primary mirror was a scatter specification. This was a problem in two respects, the mirror substrate was Zerodur and the scatter angle was too close to specular to measure with a scatterometer. The near zero expansion Zerodur is a microcrystalline glass ceramic that scatters light when illuminated so a scatter test could not be used during polishing. Also, the scatter angle in the specification was so close to specular that the detector in a scatterometer partially obscured the scattered light path and could not be used even if the substrate did not scatter.

Kashmira Tayabala, et. al., “Use of the PSD and incident angle adjustments to investigate near specular scatter from smooth surfaces”, Proc. SPIE, 8838 (2013) showed that the MicroFinish Topographer (MFT) could measure surface roughness over sufficiently long distances to infer the magnitude of the near specular angle scatter. Given this insight, the MFT was used to show the Inouye Solar Telescope primary met the near specular angle scatter specification, Chang Jin Oh, et. al., “Fabrication and Testing of 4.2m Off-Axis Aspheric Primary Mirror of Daniel K. Inouye Solar Telescope”, Proc. SPIE, 9912 (2016).

About the Author

Robert Parks

Robert Parks

Mr. Parks received a BA and MA in physics from Ohio Wesleyan University and Williams College, respectively. His career started at Eastman Kodak Company as an optical engineer and then went on to Itek Corp. as an optical test engineer.

He learned about optical fabrication during a 4 year stay at Frank Cooke, Inc. This experience led to a position as manager of the optics shop at the College of Optical Sciences at the Univ. of Arizona and where he worked for 12 years and had a title of Assistant Research Professor. During that time he had the opportunity to write about the projects in the shop and the optical fabrication and testing techniques used there including papers about absolute testing and the installation and used of a 5 m swing precision optical generator.

Mr. Parks left the University in 1989 to start a consulting business specializing in optical fabrication and testing. Among the consulting projects was one working for the Allen Board of Investigation for the Hubble Telescope where he stayed in residence at HDOS for the duration of the investigation. In 1992 he formed Optical Perspectives Group, LLC as a partnership with Bill Kuhn, then a PhD student at Optical Sciences.

The consulting and experience with Optical Perspectives provided many more opportunities to publish work on optical test methods and applications. While still at Optical Sciences, Mr. Parks became involved in standards work and for twenty years was one of the US representatives to the ISO Technical Committee 172 on Optics and Optical Instruments. For two years he was the Chairman of the ISO Subcommittee 1 for Fundamental Optical standards. Recently Mr. Parks temporarily rejoined Optical Sciences part time helping support optical fabrication projects and teaching as part of the Opto-Mechanics program.

Bob is a member of the Optical Society of America, a Fellow and past Board member of SPIE and a member and past President of the American Society for Precision Engineering. He is author or co-author of well over 100 papers and articles about optical fabrication and testing, and co-inventor on 6 US patents. He remains active in development of new methods of optical testing and alignment.

Case Studies & Testimonials

  • "You are always responsive and give us lots of useful information!!"

    Dr. Shaojie Chen
    Dunlap Institute for Astronomy and Astrophysics
    University of Toronto

     

  • "As always we are very much loving the instrument, I personally love the camera upgrade from what I'm used to!"

    Weslin Pullen
    Hart Scientific Consulting International, LLC
    Tucson, Arizona

     

  • The PSM is an ideal tool for finding the center of curvature of a ball or the axis of a cylinder. The question is for how small a ball or cylinder can the PSM do this?

    The smallest article that was readily available was a piece of monofilament 8 pound test fishing line that was 290 μm in diameter. There was no problem finding the axis of the fishline, and separating the Cat’s eye reflection from the surface from the confocal reflection of the axis. The experiment was done with a 5x objective, and the result would have been even more definitive using a 10x objective.

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