Among other applications, ultra-low expansion (ULE) glass is commonly used as material for laser cavities. ULE glass is a trademark of Corning Incorporated and consists for the most part of SiO2 with additionally about 9% TiO2. ULE cavities were recently proposed to measure helium refractivity for a new fundamental realization of the pascal.1–3 In Ref. 1, it was reported that the diffusion of helium into ULE glass caused a length change of the ULE spacer. Another challenge in this application may be a pumping effect of ULE for helium or outgassing of previously absorbed helium. To estimate the impact of helium absorption, we have measured the diffusion constant and solubility of helium in ULE near 23 °C.
We received a sample of ULE glass code 7972 (charge no. 12 204 ANT1) from the Corning company and cut this sample into rectangular plates. For this investigation,...