宽带、圆偏振的宏微脉冲激光能够有效地激发大气中间层钠原子，为自适应光学波前探测提供较多的回波光子数。在二能级光学Bloch方程的基础上，考虑不同大气湍流模式下激光光强在大气中间层的分布，通过数值模拟的方法，计算三种大气湍流模式下的钠信标回波光子数，然后根据经验确定大气相干长度的范围，估算宏微脉冲激发钠信标回波光子数的平均值，所得的平均值与实验测量值比较接近。由于宏微脉冲激光与钠原子作用可以忽略反冲、下抽运、地磁场等因素的影响，因此可以用计算有效截面的方法估算钠信标回波光子数。但是由于这种方法没有考虑激光的偏振态、光束质量因子以及光强的随机分布对钠原子激发态概率的影响，导致计算结果偏小。

The macro-micropulse laser with broadband and circular polarization can effectively excite the sodium atoms in the mesosphere, which can offer more return photons for the wave-front sensing of the adaptive optics. Based on the two-level Bloch equation, considering the distribution of laser intensity under the different models for atmosphere turbulence in the mesosphere, the number of return photons for sodium laser beacons is calculated under the three models for atmospheric turbulence by the method of numerical simulation. Then, the scale of atmosphere coherent length is conjectured according to experience and the average value for the number of return photons is calculated. The average value is relatively close to the experimental values. Because the effects of the recoil, down-pumping and geomagnetic field can be neglected, the return photons can be computed by the effective absorption cross-section. However, this method leads to the smaller results of computation because there is no consideration of the influence of laser polarization, beam quality factor and intensity distribution on the probability of excited states.