Construction of the LISA back-side fibre link interferometer prototype

The Laser Interferometer Space Antenna (LISA) is a joint ESA NASA mission to be launched in 2018. It is an interferometric gravitational wave detector with a measurement band going from 0.1 mHz to 1 Hz. The conceptual interferometer design is unique and includes many challenging aspects that must be analysed in terms of their stability in advance to the mission. One of these new features is the so-called back-side fibre link, which connects the two optical benches on-board each spacecraft. In its optical fibre, two frequency shifted laser beams are counter-propagating. LISA will only reach its design sensitivity, if these two beams inside this fibre experience the same pathlength changes down to a level of approximately 1 pm/\sqrt{\rm Hz} in the mHz range. In this paper, we present the construction of a quasi-monolithic interferometer that represents a cutout of the LISA interferometry concerning the back-side fibre link. In order to ensure a high thermal and mechanical stability of the interferometer, the hydroxide-catalysis bonding technique was applied. For the construction of the interferometer, a number of new alignment techniques and solutions were developed that are suitable for LISA prototype experiments