COMPARISON OF 2 HIGH-PRECISION NONDESTRUCTIVE MEASUREMENT METHODS FOREVALUATING THERMAL-EXPANSION DIFFERENCES IN THE 8.3-M ULTRALOW-EXPANSION SUBARU PRIMARY MIRROR BLANK

The building blocks for fabricating the 8.3-m Subaru primary mirror bl ank are ultralow-expansin solid hexagonal units that were subjected to rigorous ultrasonic examination to establish thermal expansion charac terization as reported by Hagy [Appl. Opt. 12, 1440 (1973)]. Following assembly of the mirror by fusion and fine annealing, photoelastic ana lyses at hex-to-hex seals were used to calculate thermal expansion dif ferences. These differences are found to be in excellent agreement wit h the ultrasonically established differences. (C) 1996 Optical Society of America