Precision Thermal Expansion Measurements on Low Expansion Optical Materials

Recent critical applications for ultralow expansion materials have required thermal expansion measurements with very high precision and accuracy. A Fizeau interferometer employing a helium-neon laser has given a precision of +/-0.1 x 10(-6) cm/cm. A second, more rapid method consists of a rod type vitreous silica dilatometer. A stirred water bath is used for specimen temperature control and a high output, linear variable differential transformer serves as the extensometer. Precision of this method is +/-0.5 x 10(-6) cm/cm. Calibration procedures and results for several low expansion materials are discussed.