Abstract
In this paper, we review the salient facts for a range of available atmosphere emulation technologies, and in the framework of the ESO Multi-Conjugate-AO demonstrator project, aptly called MAD, we present our phase screen test results for silver-sodium ion-exchange, transmissive phase screens. We find (a) that the measured power spectrum of phase fluctuations is consistent with the input Von Karman spectrum and (b) that by tracking the best focus of ten spots formed by a silver-sodium ion-exchange micro-lens array, it was found that the wavelength dependence of 1.266μm of phase-shift is 1.5±2.5% relative to air in the wavelength range 550nm to 800μm.
Additionally, we present our optical design and specifications for MAPS, the Multi-Atmospheric Phase screens and Stars instrument that will be used to test MAD before shipment to the VLT. It includes glass screens conjugate to the 0.25km, 3.0km, and 9.0km atmospheric layers above the telescope. We explain the reasoning behind the choice of pupil size and implications for phase screen proximity, footprint sizes, and wind speed gradients. Our design mimics the VLT Nasmyth F/15 focal plane in terms of plate scale, field of view, high Strehl, and field curvature.
