Using Allvar to Create Near-Zero CTE Structures Suitable for Space Missions*

ALLVAR Alloys are Titanium-based metals which have the unique property of a negative coefficient of thermal expansion (CTE). They enable the construction of non-magnetic compact support structures with near zero CTE by matching it with positive CTE materials such as regular Titanium. These structures will find many applications in space telescope missions for significantly reducing the wavefront error caused by differential thermal expansion. Our group is characterizing a test structure in which two 25 cm Zerodur® blanks are separated by three low CTE bipods made from Ti-6Al-4V and ALLVAR Alloy-30. If properly matched, these bipods should separate the Zerodur® blanks with pm/√Hz stability. If successful, this work might help qualify these negative CTE alloys as a spacer material for use in the optical path of interferometric gravitational wave observatories such as LISA.