Hellemeier Joschua A, Hickson Paul, Labadie Lucas
J Opt Soc Am A Opt Image Sci Vis. 2017 Aug 1;34(8):1376-1382. doi: 10.1364/JOSAA.34.001376.
A simulation modeling excitation of the sodium D line by nanosecond time scale pulsed lasers is described. By numerically integrating transition rates in the sodium hyperfine structure, the return flux per sodium atom is predicted as a function of laser power. The simulation should be useful for studies of mesospheric sodium and adaptive optics. Applications include the estimation of sodium column density from lidar return flux, and of laser guide star brightness for different pulsed laser formats. The simulation assumes that the pulse repetition frequency is sufficiently low (smaller than a few kilohertz) that atomic collisions restore local thermodynamic equilibrium between pulses. It is also assumed that the pulse length is short compared to the Larmor precession time scale. The numerical results are well-approximated by a simple analytic model for a three-level atom. The number of emitted photons is found to be primarily dependent on the product of the length of the laser pulse and the energy density.
描述了用纳秒时间尺度脉冲激光激发钠D线的模拟建模。通过对钠超精细结构中的跃迁速率进行数值积分，预测了每个钠原子的返回通量作为激光功率的函数。该模拟对于中层钠和自适应光学的研究应该是有用的。应用包括根据激光雷达返回通量估算钠柱密度，以及估算不同脉冲激光格式下激光导星的亮度。该模拟假设脉冲重复频率足够低（小于几千赫兹），以至于原子碰撞在脉冲之间恢复局部热力学平衡。还假设脉冲长度与拉莫尔进动时间尺度相比很短。数值结果可以用一个简单的三能级原子解析模型很好地近似。发现发射光子的数量主要取决于激光脉冲长度和能量密度的乘积。
