Dark tip-tilt sensing
  Dark wavefront sensing in its simplest and more crude form is a quad-cell with a round spot of dark ink acting as occulting disk at the center. This sensor exhibits fainter limiting magnitude than a conventional quad-cell, providing that the size of the occulting disk is slightly smaller than the size of the spot and smaller than the residual jitter movement in closed loop. We present simulations focusing a generic Adaptive Optics system using Natural Guide Stars to provide the tip-tilt signal. We consider a jitter spectrum of the residual correction including amplitudes exceeding the dark disk size. 
Carmelo Arcidiacono, Roberto Ragazzoni, Valentina Viotto, Maria   Bergomi, Jacopo Farinato, Demetrio Magrin, Marco Dima, Mar...
astro-ph.IM