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23 June 1995 Michelson-like interferometer in flowing air for measuring the thermal expansion coefficient of an optical table
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This paper deals with a Michelson-like interferometric apparatus in air to determine the thermal stability of an optical table. The flowing air is an efficient tool to uniform the temperature of the objects under test. With some precautions it is possible to use the noisy modulations in the interference pattern, due to the presence of air, to perform a 'temperature- scanned' interferometric measurement. The derivative in temperature of the refraction index of air is negative, less the 2 micrometers per K, nearly constant in a small temperature range. Therefore in the center of the Haidinger rings a monotone sinusoidal irradiance versus temperature can be calculated. The FFT analysis of this signal shows a 'quasi-monochromatic' line in the inverse temperature domain whose position is proportional to the thermal expansion coefficient of the air. The actual signal will depend also from the thermal stresses undergone by the interferometer arms. The FFT analysis of a set of experimental data shows a line shifted from the calculated 'pure-air' position. The amount of this shift is proportional to the equivalent thermal expansion coefficient of the table: (alpha) z equals -2.4 X 10-7 +/- 1.2 X 10-8K-1 in the temperature range t equals [ 17.7, 22.5 ] degree(s) C. The resolution of the method and the main sources of noise are discussed.
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Valter Giaretto, Elio Miraldi, and Giuseppe Ruscica "Michelson-like interferometer in flowing air for measuring the thermal expansion coefficient of an optical table", Proc. SPIE 2545, Interferometry VII: Applications, (23 June 1995);

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