A Hybrid Pulsed Rayleigh-sodium Laser Guide Star Adaptive Optics System for Strong Turbulence Observations

Sodium laser guide star (LGS) adaptive optics (AO) systems have become highly productive tools for all-sky astronomical observations with large telescopes. However, the performance of these systems is limited by the brightness of the sodium LGS and the number of wavefront sensor subapertures used during strong atmospheric turbulence. We propose a hybrid pulsed Rayleigh-sodium LGS AO system that exhibits an improved Strehl ratio of 55% to eliminate the effects of partial wavefront sampling for limited sodium LGS brightness in K-band. This technique uses the Rayleigh scattering signal, a byproduct of pulsed sodium LGS, with temporal-gating approach. This system comprises a Rayleigh LGS to direct light toward the wavefront sensor under a wide variety of atmospheric conditions. The Rayleigh beacon provides high-order corrections to the low-altitude layers. Any remaining distortions from higher layers typically exist on a much larger scale, which can be sampled with comparatively larger subapertures. This approach could improve the performance of large optics-infrared telescopes equipped with hybrid Rayleigh-sodium LGS AO systems during strong turbulence events.