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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1983 Excerpt: ...(2) can be polished very smooth 5, (3) can in some grades be quite homogeneous and nearly stria-, bubble-, and inclusion-free, and (4) has excellent opto-mechanical and thermo-structural properties. Opticians expect these properties, and it is easy to assume that Work partially supported by Navy Independent Research funds, lumbers in brackets indicate the literature references at the end of the paper. the lower expansion materials will have similar characteristics. Such an assumption needs to be examined experimentally. This paper discusses two such experiments. One is a simple technique for approximately measuring the thermal coefficient of expansion of these low expansion materials. The second is an investigation of their dimensional stability after thermal cycling such as might occur during a coating process. Thermal shock resistance is also investigated. Expansion Coefficient To accurately measure the thermal expansion coefficient of a low expansion material, an elaborate laboratory setup is required 6. However, an approximate value should be obtainable by producing interference fringes between the test sample, polished optically flat, and a reference flat. The top surface of the test sample is heated and the expansion coefficient inferred from the way the fringes move. The bowing of a simply supported disk-shaped surface of thickness I and radius a is given by 7 r,2 2s 1/2. r z 1/2 Q 2 1/2 n w =-6a(a I p / T(z, t)zdz + TTi-y (1 + v)o / Tdz-S / Tdz-z / Tzdz, (1) J-1/2 U-v; L o v- /2 2(1/2)-1/2 J where the origin of cylindrical coordinates is at the disk center, the z coordinate is measured normal to the surface, and p is the radial coordinate. The temperature T is a function of z and time t, w is the bowing normal to the disk surface caused by ...

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