CHOUGH: implementation and performance of a high-order 4m AO demonstrator

CHOUGH is a small, fast project to provide an experimental on-sky high-order SCAO capability to the 4.2m WHT telescope. The basic goal has r(0)-sized sub-apertures with the aim of achieving high-Strehl ratios (> 0.5) in the visible (> 650 nm). It achieves this by including itself into the CANARY experiment: CHOUGH is mounted as a breadboard and intercepts the beam within CANARY via a periscope. In doing so, it takes advantage of the mature CANARY infrastructure, but add new AO capabilities. The key instruments that CHOUGH brings to CANARY are: an atmospheric dispersion compensator; a 32 x 32 (1000 actuator) MEMS deformable mirror; 31 x 31 wavefront sensor; and a complementary (narrow-field) imager. CANARY provides a 241-actuator DM, tip/tilt mirror, and comprehensive off-sky alignment facility together with a RTC. In this work, we describe the CHOUGH sub-systems: backbone, ADC, MEMS-DM, HOWFS, CAWS, and NFSI.