Multi-conjugate adaptive optics with hybrid laser beacon systems

Results for a multi-conjugate adaptive optical (MCAO) system with multiple laser beacons at multiple altitudes are presented in this paper. The use of multi-conjugate deformable mirrors (DM's) increases the corrected field of view of an adaptive optical telescope system. This improves the imaging capability for extended astronomical objects such as planets, galaxies, and nebulae. Multiple laser beacons, as opposed to multiple natural guide stars, are needed to achieve a useful degree of sky coverage. The use of laser beacons at multiple altitudes in a hybrid laser beacon configuration has been shown in previous papers to reduce both focus and tilt anisoplanatism. In this study we combine all three of these aspects. The hybrid beacon scenarios used in this study consists of multiple high altitude sodium beacons at 90 km and/or multiple low altitude Rayleigh beacons at 10 to 20 km. We present results for an 8-m class telescope for 2 and 3 different DM conjugate altitudes. For each of these MCAO configurations the following parameters are varied: number of Rayleigh beacons, number of Rayleigh beacon wavefront sensor (WFS) subapertures, Rayleigh beacon altitudes for the Rayleigh/sodium configuration, number of natural beacons for tip/tilt correction, and number of natural beacon WFS subapertures. When the WFS subaperture for the natural beacon is greater than 1 x 1 it contributes to the higher order correction in addition to being used for tip/tilt correction. Results are compared in terms of Strehl Ratio for the J, H, and K band.