System driven design and validation of a cryogenic optical delay line for DARWIN

The DARWIN mission of ESA will search for earth-like exo-planets orbiting suitable target stars in our solar neighborhood, and will allow direct low resolution spectroscopy of exo-planetary atmospheres. The optical enabling technology for DARWIN is high-contrast destructive Nulling interferometry of stellar light, necessitating utmost symmetry of optical beam trains. We report the system driven design of a cryogenic optical delay line compatible with the extremely tight requirements imposed by optical symmetry. After analysis of requirements and system aspects, we describe the actual design implementations and our validation scheme. We conclude with an outlook on integration of this ODL into a cryogenic ground-based testbed for DARWIN Nulling interferometry.