Abstract

Most aspheric mirrors have been tested by the null lens or computer-generated hologram method. This approach, however, requires that the shape of the surface be similar to the target shape; otherwise testing may not be possible or correct. The Hartmann test has an advantage in that it has a larger dynamic range than a general interferometer, which means that the surface can be tested beginning at an early stage of the polishing process. We suggest use of the null Hartmann test in conjunction with a phase-shifting interferometer for the measurement of a 0.9-m aspheric concave mirror. This setup was able to measure the surface with a large surface form error as well as with a small error without sacrificing any measurement accuracy. Using this setup, we have successfully polished a surface to remove approximately 1 µm of peak-to-valley wave-front error of a total of 39 µm of error during 1 month of polishing.

© 2005 Optical Society of America

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References

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  1. CELT, The California Extremely Large Telescope, <a href= "http://celt.ucolick.org/">http://celt.ucolick.org/</a>.
  2. NPL, NPL, and EURO 50 telescope, <a href= "http://www.npl.co.uk/length/dmet/euro50.html">http://www.npl.co.uk/length/dmet/euro50.html</a>.
  3. OWL, 100-m OWL telescope concept, <a href= "http://www.eso.org/projects/owl/owl_design.html">http://www.eso.org/projects/owl/owl_design.html</a>.
  4. H. S. Yang, S. W. Kim, and D. D. Walker, �??A novel profilometer for nanometric form assessment for large machined surfaces,�?? Key Eng. Mater. 257, 225-230 (2004).
    [CrossRef]
  5. D. Malacara, Optical Shop Testing (Wiley, New York, 1992), Chap. 10.
  6. V. A. Zverev, S. A. Rodionov, M. N. Sokol'skii, and V. V. Usoskin, �??Testing of the primary mirror of the LAT (Large Azimuthal Telescope) by the Hartmann method during its manufacture, �?? Sov. J. Opt. Technol. 44, 127-129 (1977).
  7. M. Servin, F. J. Cuevas, D. Malacara, and J. L. Marroquin, �??Direct ray aberration estimation in Hartmanngrams by use of a regularized phase-tracking system,�?? Appl. Opt. 38, 2862-2869 (1999).
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  10. W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1990), Chap. 4.
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    [CrossRef]

Appl. Opt.

J. Opt. Soc. Am.

Key Eng. Mater.

H. S. Yang, S. W. Kim, and D. D. Walker, �??A novel profilometer for nanometric form assessment for large machined surfaces,�?? Key Eng. Mater. 257, 225-230 (2004).
[CrossRef]

Proc. SPIE

J. Burge, �??A null test for null correctors: error analysis, �?? in Quality and Reliability for Optical Systems, J. W. Bilbro and R. E. Parks, eds., Proc. SPIE 1993, 86-97 (1993).

Sov. J. Opt. Technol.

V. A. Zverev, S. A. Rodionov, M. N. Sokol'skii, and V. V. Usoskin, �??Testing of the primary mirror of the LAT (Large Azimuthal Telescope) by the Hartmann method during its manufacture, �?? Sov. J. Opt. Technol. 44, 127-129 (1977).

Other

W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1990), Chap. 4.

D. Malacara, Optical Shop Testing (Wiley, New York, 1992), Chap. 10.

CELT, The California Extremely Large Telescope, <a href= "http://celt.ucolick.org/">http://celt.ucolick.org/</a>.

NPL, NPL, and EURO 50 telescope, <a href= "http://www.npl.co.uk/length/dmet/euro50.html">http://www.npl.co.uk/length/dmet/euro50.html</a>.

OWL, 100-m OWL telescope concept, <a href= "http://www.eso.org/projects/owl/owl_design.html">http://www.eso.org/projects/owl/owl_design.html</a>.

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Figures (8)

Fig. 1.
Fig. 1.

Experimental setup for the test of a large aspheric mirror by using dual sensors.

Fig. 2.
Fig. 2.

(a) General configuration for the test of a target asphere by use of a Hartmann sensor. (b) The wave-front slope at the image plane.

Fig. 3.
Fig. 3.

Configuration of null correctors.

Fig. 4.
Fig. 4.

Test results for the verification mirror: (a) Form Talysurf, (b) interferometer.

Fig. 5.
Fig. 5.

Comparison of the results of measurement of the high-quality doublet with (a) ZYGO phase-shifting interferometer and (b) the Hartmann sensor. OPD is optical path difference.

Fig. 6.
Fig. 6.

Differences between the rms WFE estimation and measurement results.

Fig. 7.
Fig. 7.

Experimental setup for the test of the 0.9-m aspheric mirror.

Fig. 8.
Fig. 8.

Test results (a) at the start of polishing and (b) after 1 month of polishing.

Equations (1)

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f ( W x ) max = S 2 1.22 λ f d ,

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