A Fiber Ring Laser Dilatometer for Measuring Thermal Expansion Coefficient of Ultralow Expansion Material

A new type of measuring system for coefficient of linear thermal expansion (CTE) of ultralow expansion (ULE) material by using a fiber ring laser is introduced in this letter. The lasing frequency of the laser is stabilized to one of the transmission peaks of the etalon filter by controlling the resonant frequency of the tunable filter. The spacer of the (Fabry-Perot type) etalon filter is made of ULE material. We could measure the CTE of ULE by measuring the optical frequency change caused by the temperature change of the etalon spacer. The combined standard uncertainty is estimated as the value of plusmn36.6 ppb/degC in the temperature range from 5degC to 60degC.