微秒脉冲激光钠导引星星群技术研究（特邀）

激光钠导引星被称为人造恒星，用于探测和校正光波经大气湍流引起的波前畸变，大幅度提高自适应光学望远镜的成像质量。采用单颗钠导引星探测的有效视场范围有限，通过多束黄激光分别激发大气电离层钠原子产生多颗钠导引星，能在较大视场内获得更清晰的目标成像，在精密天文观测、空间目标探测等领域具有重要应用。文中重点介绍了微秒脉冲激光钠导引星星群的产生，基于100 W级微秒脉冲激光，采用小角度精密偏振分光/并束调控的专利技术，在丽江天文台通过一台发射望远镜将四束20 W/束、重复频率kHz、脉冲宽度百微秒的钠激光发射到天空，在40"观测视场内生成四颗导引星，星群构型可调控，如线形、平行四边形、菱形和正方形等，每颗钠导引星亮度约为V波段8等星，光斑大小约3.25"。利用脉冲同步控制技术，钠导引星回波信号可以避免瑞利散射光的干扰，从而获得更高的空间分辨率。这为大口径天文望远镜多层共轭校正系统的研制提供技术参考。

Technology of microsecond-pulse sodium laser guide stars asterism (Invited)

Sodium laser guide stars (LGS), known as artificial stars, can be used to detect and correct wavefront aberrations induced by atmospheric turbulence, which can significantly improve the adaptive-optical telescope's imaging quality. Due to the limited corrected field of view of single LGS, multiple sodium LGS, created by exciting sodium atoms in the Earth's mesosphere via multiple yellow laser beams, is developed to yield high-resolution imaging in a much larger field-of-view, which has important applications in the fields of precision astronomical observation and space target detection. The successful implementation of microsecond-pulse sodium guidestars constellation via 100 W level pulsed sodium laser was reported, based on a small angle precise polarized combining and splitting technology. At Lijiang Observatory, four-ways~20 W/beam yellow laser beam with kHz repetition-rate and hundred-μs pulse width were projected up to the sky through one launching telescope, and generated a distinctive four-point grouping on a 40" field of view with variable configurations of linear, parallelogram, rhomboid and square. The spot size of each guide star was about 3.25" and the corresponding brightness was around 8 magnitude in V band. The sodium return signal could well avoid Rayleigh light interference by the pulse synchro controlling technology to deliver higher spatial resolution. This could serve as a technical reference for multi-conjugate correction systems on large-aperture astronomical telescopes.