Embedded Model Control: Application to Interferometric Metrology Lines

In a recent paper principles and control of Fabry-Perot interferometers (FPI) have been presented, showing a few applications in the field of space and precision engineering. Among them, metrology lines were mentioned, aiming to reveal sub-nanometric displacements in view of dimensional stabilization and monitoring of demanding space telescopes. The core is a confocal optical cavity, in vacuum, whose light path is sensible to dimensional variations. The latter are tracked and revealed by a frequency actuator which acting on the incident laser light keeps the FPI signal close to zero. Concepts and digital control of metrology lines will be outlined and experiments on a ground breadboard under space conditions (160 K) will be discussed. Due to on-ground contingencies, a displacement actuator was also active, which asked for actuator coordination