Advancing high contrast interferometry: new metrology system for the VLTI

Abstract

Future high contrast interferometric observations with the Very Large Telescope Interferometer (VLTI) require nanometer level control of optical path variations to preserve fringe stability and maximize sensitivity. Within the framework of the PLANETES project, a dedicated laser metrology system is being developed to monitor optical path variations over the full interferometric beam train, complementing the dual field observing strategy by providing real time, absolute optical path difference measurements between the VLTI laboratory and the telescope level. The metrology system distributes a 1064nm laser source through optical fibers to a network of Mach-Zehnder interferometers, enabling continuous monitoring of vibrations affecting the optical train. This paper presents the metrology concept and optical architecture, along with initial laboratory performance results from the metrology testbed. Measurements demonstrate accurate retrieval of controlled optical path perturbations and broadband vibration signals, validating the proposed architecture for dynamic optical path sensing.