Fratricide effect on ELTs

¹ Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA), Observatoire de Paris, CNRS, UPMC, Universite Paris Diderot, 5 places Jules Janssen, 92195 Meudon France
Groupement d'Interet Scientifique PHASE (Partenariat Haute resolution Angulaire Sol Espace) between ON-ERA, Observatoire de Paris, CNRS and Universite Paris Diderot
² Gemini Observatory Southern Operation Center, c/o AURA, Casilla 603, La Serena, Chile

^a e-mail: damien.gratadour@obspm.fr

Abstract

In this paper, we present the results of our study of the so-called fratricide effect, i.e. the increased background observed in a number of a wavefront sensor’s sub-apertures, due to the scattering of laser photons on dust or clouds particles or air molecules located along a laser beam. Using the formalism developed by the LIDAR community, we computed the background levels to be expected on various kinds of adaptive optics systems to be installed eventually on the E-ELT (42 m). In the case of pure Rayleigh backscattering, the induced background, expected to be constant (as it mainly depends on the air molecules density), is not a show stopper. We however stress that in the presence of sub-visible clouds or dust particles along the laser beam, the significant amount of induced background, which is likely to be variable, could potentially affect the performance of AO systems.