Exploiting the pyramid WFS gain using a deformable lens as an NCPA corrector

Abstract

Pyramid wavefront sensors are widely used in adaptive optics systems, due to their advantages in terms of sensitivity with respect to other wavefront sensors such as the Shack-Hartmann. However, especially in extreme adaptive optics applications, Non-Common Path Aberration (NCPAs) cause image distortions that can hinder the scientific throughput. NCPAs are usually corrected introducing offsets on the pyramid closed-loop control systems, but the consequent increase in the size of the star image on the pyramid pin leads to a decrease in sensitivity that compromises the aforementioned advantages. In principle, these offsets can be counter-balanced by introducing an active optical element in the wavefront sensing channel, recovering the full sensitivity of the pyramid. In this framework, we are studying the capability of Multi-Actuator deformable Lenses to recover such NCPAs. We present in this paper the result obtained on the test-bench that has been realized at CNR-IFN Institute in Padova, with the collaboration of INAF-Padova, aiming at the NCPAs correction by the means of a multi-actuator deformable lens inserted in the sensing path, in order to recover the optimal working conditions and the ideal magnitude gain of the pyramid.