<title>Thermal expansion measurement of gauge blocks</title>

Abstract

An instrument for the measurement of the thermal expansion coefficient near room temperature of gauge blocks and other samples of similar shape and size has been developed. The length dilation is measured by a differentia plane mirror interferometer. A special interference phase detection technique compensates for non-linearity errors caused by polarization mixing. In combination with an electronic phase meter this allows to achieve nanometer accuracy. Since the measurements are done in vacuum, no compensation for the refractive index of air has to be made. For samples with good thermal conductivity the slow heat exchange by thermal radiation allows for a small temperature gradient of the sample and a good stability in the thermal equilibrium. From the thermal expansion curve, measured in a temperature range typically between 10 degrees C and 30 degrees C, the linear and quadratic expansion coefficients are evaluated at 20 degrees C, the reference temperature for length. It is shown, that for the investigated gauge block materials the room temperature expansion can be very accurately described with two coefficients within a few parts in 109 per degree. A detailed analysis of the measurement uncertainty demonstrates the capability of the measurement instrument, which is confirmed by the results of an international comparison.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.