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The application of a sodium laser guide star is the key difference between a modern adaptive optics system and traditional adaptive optics system. Especially in system such as multiconjugate adaptive optics, a sodium laser guide star asterism that is formed by several laser guide stars in a certain pattern is required to probe more atmospheric turbulence in different directions. To achieve this, a sodium laser guide star asterism launching platform is required. In this paper, we introduce the sodium laser guide star asterism launching platform built and tested on the 1.8 m telescope of Gaomeigu Observatory. The platform has two functions: one function is to compare the performance of sodium laser guide stars generated by different lasers at the same place, and the other function is to generate a sodium laser guide star asterism with an adjustable shape. The field test results at the beginning of 2021 verified the important role of the platform, which is also the first time that a sodium laser guide star asterism was realized in China.

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 ∼20 W yellow laser beam with kHz repetition-rate and hundred-μs 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.

Sodium laser guide star (LGS) system has become one of the critical components in modern astronomical adaptive optics system (AOS), especially for the next-generation extremely large telescopes, such as the Thirty Meter Telescope and the European Extremely Large Telescope. Since the wavefront detection performance of AOS is directly related to the brightness of LGS, it is important for AOS to maximize its photon generation efficiency by all means. Sodium D-2b line repumping is such a technique that can greatly increase the returned photons for either sodium continuous wave (CW) laser or pulsed laser. This technique has been studied theoretically and field tested with a 20 W CW laser by European Southern Observatory team. However, field test results of a 20 W class pulsed laser with D-2b repumping have not been reported yet. In this paper, our latest field test results with theoretical comparison of D-2b repumping with a 20 W quasi-continuous wave (QCW) pulsed laser will be presented. With a linearly polarized beam, approximate 40% photon return enhancement was achieved when 10% of laser power was detuned to D-2b line, which agreed well with results from a rate equation-based Monte Carlo photon return simulation program. Both experiment and simulation results indicate that with a higher laser intensity projected at the sodium layer, the D-2b repumping will be more effective.