The pyramid wavefront sensor for the high order testbench (HOT)

The High Order Testbench (HOT) is a joint experiment of ESO, Durham University and Arcetri Observatory to built and test in laboratory the performance of Shack-Hartmann and pyramid sensor in a high-order correction loop using a 32x32 actuators MEMS DM. This paper will describe the pyramid wavefront sensor unit developed in Arcetri and now installed in the HOT bench at ESO premises. In the first part of this paper we will describe the pyramid wavefront sensor opto-mechanics and its real-time computer realized with a commercial Linux-PC. In the second part we will show the sensor integration and alignment in the HOT bench and the experimental results obtained at ESO labs. Particular attention will be paid to the implementation of the modal control strategy, like modal basis definition, orthogonalization on the real pupil, and control of edge actuators. A stable closed loop controlling up to 667 modes has been achieved obtaining a Strehl ratio of 90 -- 93% in H band.