First Implementation of Pulsed Sodium Guidestars Constellation for Large-aperture Multi-conjugate Adaptive Optics Telescopes

Multiple synthetic beacons are required for atmospheric-turbulence compensation in an extended-field-of-view multi-conjugate adaptive optics (MCAO) telescope. In this paper, we report on the first successful implementation of a microsecond-pulse sodium guidestars constellation laser system, based on a small angle precise polarized combining and splitting technology. At Lijiang Observatory of China, four-ways similar to 20 W yellow laser beam with kHz repetition-rate and hundred-mu s pulse width were projected into the sky through one small-aperture launching telescope, and generated a distinctive four-point grouping on a field of view of 40 '' with variable configurations of linear, parallelogram, rhomboid and square. The sodium return signal could easily avoid Rayleigh light interference by the pulse synchro controlling technology delivering a higher spatial resolution. Moreover, the increase in return photons for alternated circularly and alternated linearly polarized light has been investigated. We believe that the above results could serve as a future reference for the MCAO system on large-aperture telescopes worldwide.