Abstract

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: $0.48\mathrm{nm}\mathrm{rms}$ in piston and $74\mathrm{nrad}\mathrm{rms}$ in tip/tilt.

© 2008 Optical Society of America

Active hexagonally segmented mirror to investigate new optical phasing technologies for segmented telescopes

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