Apparatus for Measuring the Thermal Expansion of Optical Materials from 30 degrees C to 250 degrees C.

An apparatus has been designed and constructed for measuring the coefficient of linear thermal expansion in the 30-250 degrees C temperature range for samples as small as 13 mm in length and 6 mm in diameter. Similarities between this apparatus and one previously built for measurements from room temperature down to 10 K are reviewed; important modifications appropriate to the high temperature range are discussed in detail. Measurements were made at 25 degrees C intervals on two infrared-transmitting optical materials: polycrystalline cadmium sulfide (Eastman Kodak Co.) and chalcogenide glass 20, composition Ge(33)Se(55)As(l2) (Texas Instruments, Inc.). Measurements were also made on a sample of Corning crown glass 8263; the results are compared with Corning data. Finally, it is shown that the thermal expansion coefficients determined with this high temperature apparatus are compatible with those obtained with the above-mentioned low temperature device.