The building blocks for fabricating the 8.3-m Subaru primary mirror blank are ultralow-expansin solid hexagonal units that were subjected to rigorous ultrasonic examination to establish thermal expansion characterization as reported by Hagy [Appl. Opt. 12, 1440 (1973)]. Following assembly of the mirror by fusion and fine annealing, photoelastic analyses at hex-to-hex seals were used to calculate thermal expansion differences. These differences are found to be in excellent agreement with the ultrasonically established differences.

© 1996 Optical Society of America

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  1. H. E. Hagy, “High precision photoelastic and ultrasonic techniques for determining absolute and differential thermal expansion of titania-silica glasses,” Appl. Opt. 12, 1440–1446 (1973).
  2. H. E. Hagy, W. D. Shirkey, “Determining absolute thermal expansion of titania-silica glasses: a refined ultrasonic method,” Appl. Opt. 14, 2099–2103 (1975).
  3. “Standard method of test for analyzing stress in glass,” ASTM F218-68, in 1995 Annual Book of Standards (American Society for Testing and Materials, Philadelphia, Pa., 1995), pp. 430–433.

1975 (1)

1973 (1)

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Figures (3)

Fig. 1
Fig. 1

Stacking configuration for the hexagonal blocks that are sealed to make the mirror blank.

Fig. 2
Fig. 2

Stresses measured at the hex-to-hex seal plane.

Fig. 3
Fig. 3

Gaussian distribution plot of differences between thermal expansion differences, i.e., those photoelastically determined minus those ultrasonically determined.

Equations (3)

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Δ α s = ( σ 1 σ 2 ) ( 1 v ) 10 9 E Δ T ,
σ = 3.14 A 10 9 K t ,
Δ α s = 0.0415 ( A 1 A 2 ) .