Dual-wavelength low-coherence instantaneous phase-shifting interferometer to measure the shape of a segmented mirror with subnanometer precision.
We present a noncontact optical metrology measuring the pistons and tip/tilt angles of the 61 hexagonal segments of a compact-sized segmented mirror. The instrument has been developed within the scope of a design study for the European Extremely Large Telescope (E-ELT). It is used as reference sensor for cophasing of the mirror segments in closed-loop control. The mirror shape is also measured by different types of stellar light-based phasing cameras whose performances will be evaluated with regard to a future E-ELT. Following a description of the system architecture, the second part of the paper presents experimental results demonstrating the achieved precision: 0.48 nm rms in piston and 74 nrad rms in tip/tilt.
FOGALE nanotech, 125, Rue de l'Hostellerie, 30900 Nîmes, France.
Rainer
R
Wilhelm
Bruno
B
Luong
Alain
A
Courteville
Sébastien
S
Estival
Frédéric
F
Gonté
Nicolas
N
Schuhler