PYRAMIR: first on-sky results from an infrared pyramid wavefront sensor

Abstract

PYRAMIR is a pyramid wavefront sensor (PWFS) for the 97-actuator AO system installed on the Calar Alto 3.5 m telescope. With its linear pupil sampling of 18 pixels, its maximum loop frequency of 140 Hz, and its sensing wavelength range from 1.1 micron to 2.4 micron it should be able to deliver reasonably high Strehl ratios at the sensing wavelength. This feature is still unique in the world of pyramid sensors. The first on-sky test of the system was carried out in March 2006. In this paper we will present the first results of this test. Strehl measurements medium atmospheric conditions, using reference stars of m_J=8mag and m_J=4 mag and were performed during this first on-sky run. A detailed comparison to simulation results will also be presented in order to confirm whether the system works up to expectances. While this experiment has not yet the potential to show for the very first time the superiority of the pyramid principle over corresponding Hartmann-Shack systems in a real telescope environment, it was confirmed that PYRAMIR performs up to expectances and a detailed comparison to the Shack-Hartmann system can be carried out in the next run.