ESA Science & Technology - LISA Pathfinder flight optical bench during construction

The LISA Pathfinder flight optical bench pictured during construction. The "tombstone" components are precision bonded to the optical bench. The bench is a 20cm by 20cm block of Zerodur ceramic glass. The components that require high precision alignment are bonded individually. The two optical beams arrive into the optical bench through the fibre injector optical subassemblies (FIOS) – seen with the green connectors. This light is then reflected and/or split by the "tombstones". One beam will reflect off the two mirrors to the front and the back of the optical bench that are being used to represent the free-falling test masses. The other beam stays within the bench.