4H-5 Optical Differential Dilatometry for the Determination of the Coefficients of Thermal Expansion of Single Crystal Solids

This work reports on the optical differential dilatometry technique applied to the measurement of thermal coefficients of expansion on crystalline X, Y, and Z cuts of quartz and langatate (LGT) samples. The assembled dilatometer uses a phase shift technique with a Michelson-type interferometer which detects the fringe patterns generated by the recombination of two beam paths which were reflected off of the metallized surfaces of two samples as they are heated within a furnace. The differential sample expansion is calculated directly from the measured interference pattern. The measured expansion data agreed well with calculated expansion data using published expansion coefficients. For instance, the expansion of X-cut quartz was measured from room temperature to approximately 155degC, and the agreement between measured data with those calculated from published values for the entire temperature range is better than 0.32 wavelengths (202.5 nm or 5.1%)