Measuring the Thermal Expansion Coefficient of Ultrastable Materials with 10−9 K−1 Uncertainty

Materials with ultralow thermal expansion and high dimensional stability find a variety of industrial and scientific applications ranging from astronomy and space applications [1,2] to fundamental research and optical atomic clockwork [3,4]. For room temperature applications most of these materials are made of glass or glass ceramics like, e.g., ultralow expansion glass (ULE) from Corning Inc. or Zerodur from Schott AG. Their coefficient of thermal expansion (CTE) is only a few 10
^-8
/K in a temperature range of 0°C to 50°C and most often shows a zero crossing around room temperature. The exceptionally small CTE can be measured interferometrically, either by means of two-beam interference as, e.g., in a Michelson interferometer [5] or by means of multiple-beam interference as in a Fabry-Pérot resonator [6,7].