Experimental Measurement of Angular Anisoplanatism for Sodium Laser Guide Star: Synchronized Range Gating Realization

Abstract

Laser Guide Star (LGS) is an ideal synthetic beacon of Adaptive Optics (AO) for compensating for the atmospheric turbulence induced wave-front distortion of the science object; however the unavoidable anisoplanatism resulting from different light experience between the LGS and the science object through turbulent atmosphere will lead to a degradation of compensation performance, especially for the angular anisoplanatism in sodium LGS AO. By using our developed Hartmann-Shack (HS) wave-front sensor with accurate range gating mechanism, the return-light spot arrays through turbulent atmosphere from the natural star and the excited sodium LGS with certain angular offsets can be synchronously collected. Different from our previously published work (Luo et al., 2018), the experimental set-up, the structural design of the range gating mechanism, and the timing design of the synchronized control are discussed emphatically in this paper. The typical experimental measurement result of the angular anisoplanatism for the sodium LGS with 10” angular offsets is just briefly presented, which is basically consistent with our previous numerical simulation result (Luo et al., 2015). The majority of Zernike-modal de-correlations between the sodium LGS and the science object occur obviously, as the sodium LGS reference moving outside of the optical path from the science object to the telescope aperture.