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Applied Optics

Applied Optics


  • Vol. 39, Iss. 16 — Jun. 1, 2000
  • pp: 2790–2804

Medium-precision null-screen testing of off-axis parabolic mirrors for segmented primary telescope optics: the Large Millimeter Telescope

Rufino Díaz-Uribe  »View Author Affiliations

Applied Optics, Vol. 39, Issue 16, pp. 2790-2804 (2000)

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The feasibility of using null screens for testing the segments of a parabolic segmented telescope mirror for the Large Millimeter Telescope (LMT) is analyzed. An algorithm for designing the null screen for testing the off-axis segments of conic surfaces is described. Actual screen designs for the different classes of segments of the LMT are presented. The sensitivity of the test and the required accuracies for the fabrication and positioning of the screen are analyzed. A measuring accuracy of ∼12 µm in surface sagitta is within the reach of the technique.

© 2000 Optical Society of America

OCIS Codes
(000.4430) General : Numerical approximation and analysis
(120.6650) Instrumentation, measurement, and metrology : Surface measurements, figure
(220.4840) Optical design and fabrication : Testing
(350.1260) Other areas of optics : Astronomical optics

Original Manuscript: July 6, 1999
Revised Manuscript: January 27, 2000
Published: June 1, 2000

Rufino Díaz-Uribe, "Medium-precision null-screen testing of off-axis parabolic mirrors for segmented primary telescope optics: the Large Millimeter Telescope," Appl. Opt. 39, 2790-2804 (2000)

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  1. Instituto Nacional de Astrofisica, Optica y Electrónica, “The Large Millimeter Telescope Homepage,” http://binizaa.inaoep.mx/ ; mail address, Apdo. Postal 51 y 216, 72000 Puebla, Pue., Mexico.
  2. L. Olmi, “The Millimeter Telescope Project: overview and optical design,” http://binizaa.inaoep.mx/pub/014/node4.html ; mail address, Five College Radio Astronomy Observatory, University of Massachusetts, Amherst, Mass. 10020.
  3. By local asphericity I mean the departure of the segment surface from the shape of a sphere whose vertex is coincident with the central point of the segment; its radius of curvature is chosen from the best fit (in the continuum least-squares sense) according to the calculation of Cardona-Núñez et al.,9 with k′ = 0. The local asphericity is a better measure of the departures of the segment surface from a spherical shape.
  4. A. B. Meinel, M. P. Meinel, “Optical testing of off-axis parabolic segments without auxiliary optical elements,” Opt. Eng. 28, 514–518 (1989). [CrossRef]
  5. R. Díaz-Uribe, M. Campos-García, “Null screen testing of fast convex aspheric surfaces,” Appl. Opt. 39, 2670–2677 (2000). [CrossRef]
  6. By the parent surface I mean the whole surface from which a section is obtained. When all the segments are placed together, the composite surface is the parent surface.
  7. G. W. Hopkins, R. N. Shagam, “Null Ronchi gratings from spot diagrams,” Appl. Opt. 16, 2602–2603 (1977). [CrossRef] [PubMed]
  8. A. Cordero-Davila, A. Cornejo-Rodriguez, O. Cardona-Nunez, “Ronchi and Hartmann tests with the same mathematical theory,” Appl. Opt. 31, 2370–2376 (1992). [CrossRef] [PubMed]
  9. O. Cardona-Nunez, A. Cornejo-Rodriguez, R. Diaz-Uribe, A. Cordero-Davila, J. Pedraza-Contreras, “Conic that best fits an off-axis conic section,” Appl. Opt. 25, 3585–3588 (1986). [CrossRef] [PubMed]
  10. C. Menchaca, D. Malacara, “Directional curvatures in a conic mirror,” Appl. Opt. 23, 3258–3259 (1984). [CrossRef] [PubMed]
  11. J. C. Wyant, “Interferometric testing of aspheric surfaces,” in Interferometric Metrology (Critical Reviews), N. A. Massie, ed., Proc. SPIE816, 19–39 (1987). [CrossRef]
  12. A. Cox, Photographic Optics (Focal Press, London, 1971), pp. 204–205.
  13. R. Diaz-Uribe, F. Granados-Agustin, “Corneal shape evaluation by using laser keratopography,” Optom. Vision Sci. 76, 40–49 (1999). [CrossRef]
  14. Note that we follow the same notation as that used in Section 3. Again, this is a reverse ray trace; however, it does not affect to the evaluation of the normal to the surface.

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