Cone-effect-free Adaptive-optics Laser-guide-star Development for the ELTs

摘要

The goal of the CALDO experiments is to demonstrate Laser Guide Star technologies which can scale directly to a 100m diameter primary aperture, and which are not compromised by the cone-effect at very large telescope diameters. The laser guide star group at ESO and the adaptive optics group at Durham have proposed two different laser wavefront sensing methods designed to meet this goal. Though based on quite different physical principles, the two methods achieve then- scalability through the use of a parallel sensing beam projected from the whole of the telescope primary mirror. They can therefore both be demonstrated by performing a scaled-down projection and sensing experiment on a smaller telescope. The CALDO experiments evaluate the ESO and Durham methods concurrently and provide a comparison with Natural Guide Star wavefront sensing, and with each other, without the uncertainty introduced into a separate evaluation by changing atmospheric conditions. The location for CALDO is the 4.2m William Herschel Telescope, which has the advantage of the GHRIL Nasmyth facility for adaptive optics experiments and which has already been used by the Durham group for shared-optics launch experiments with a laser guide star. We describe the ESO and Durham methods, the current progress on the experimental subsystems, and the projected timescales for the experiments.