• Process optimization for efficient convergence in large optics fabrication

      Oh, Chang Jin; Martin, Hubert M.; Lowman, Andrew E.; Smith, Greg A.; Univ Arizona, Coll Opt Sci; Univ Arizona, Steward Observ (SPIE-INT SOC OPTICAL ENGINEERING, 2018)
      Large optic fabrication is a delicate and time consuming process. Obtaining a large prime optic is often in the critical path of a project and poses a serious risk to both the schedule and budget. The Optical Engineering and Fabrication Facility (OEFF) at the College of Optical Sciences, the University of Arizona, has developed a new way of optimizing its large optic fabrication process for maximum efficiency in convergence. The new process optimization takes the amount of stock material removal, tool characteristics, metrology uncertainty, optic prescription, optic material properties, and resource availability as input parameters and provides an optimized process along with an achievable convergence. This paper presents technical details of the new process optimization and demonstrates performance on 6.5m mirror fabrication at the University of Arizona. Two case studies for an 8.4m GMT off-axis primary mirror segment and a 3.1m TMT convex secondary mirror fabrication are also presented.
    • The structure function as a metric for roughness and figure

      Parks, Robert E.; Tuell, Michael T.; Univ Arizona, Steward Observ; Optical Perspectives Group, LLC (United States); The Univ. of Arizona (United States) (SPIE-INT SOC OPTICAL ENGINEERING, 2016-09-27)
      As optical designs become more sophisticated and incorporate aspheric and free form surfaces, the need to specify limits on mid-spatial frequency manufacturing errors becomes more critical, particularly as we better understand the effects of these errors on image quality. While there already exist methods based on Fourier analysis to specify these errors in most commercial interferometry software, the method of calculation and the power spectral density (PSD) results remain obscure to many in the optical design and manufacturing field. We suggest that the structure functions (SF) contains the same information as in the Fourier based PSD but in a way that is much more transparent to analysis, interpretation and application as a specification. The units of measure are more familiar and the concept behind the analysis is simpler to understand. Further, the information contained in the structure function (or PSD) allows a complete specification of an optical surface from the finest measurable detail of roughness to the overall figure. We discuss the origin of the structure function in the field of astronomy to describe the effects of air turbulence on image quality, the simple mathematical definition of the structure function and its easy means of calculation and how its results should be scaled depending on the location of the optical surface in a system from pupil to image plane. Finally, we give an example of how to write a specification of an optical surface using the structure function.