PERSEE, the dynamic nulling demonstrator: recent progress on the cophasing system

Spectral characterization of exo-planets can be made by nulling interferometers. In this context, several projectshavebeen proposed such as DARWIN, FKSI, PEGASEand TPF, space-based, and ALADDIN, ground-based. Tostabilize the beams with the requirednanometric accuracy, a cophasingsystem is required, made of piston/tip/tiltactuators on each arm and piston/tip-tilt sensors. The demonstration of the feasibility of such a cophasing systemis a central issue.In this goal, a laboratory breadboard named PERSEE i s under integration. Main goals of PERSEE are thedemonstration of a polychromatic null from 1 .65 µ mto3.3 µ mwitha10 Š 4 rejection rate and a 10 Š 5 stabilitydespite the introduction of realisti c perturbations, the study of the inter faces with formation-”ying spacecraftsand the joint operation of the cophasing system with the nuller.We describe the principle of the cophasing system made by Onera, operating in the [0 .8 Š 1] µ m (tip/tilt)and [0 .8 Š 1.5] µ m (piston) spectral bands. Emphasis is put on the piston sensor and its close integration withthe nuller.Keywords: Interferometry, nulling, Persee, Pegase, fringe tracking, ground demonstration