Theory of mesospheric sodium fluorescence excited by pulse trains.
Theory of mesospheric sodium fluorescence excited by pulse trains.
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DOI：
10.1364/ao.31.000785
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发表时间：
1992-02
期刊：
影响因子：
1.9
通讯作者：
P. Milonni;L. Thode
中科院分区：
文献类型：
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作者：
P. Milonni;L. Thode
我们描述了由一系列脉冲激发的中间层钠共振荧光的两级模型。对于与 16 ns 自然寿命相比较短的脉冲持续时间，种群率方程是不够的，必须用密度矩阵 (Bloch) 方程代替。我们简要对比这两种方法并讨论与脉冲串激励相关的几个问题。描述了原子速度平均值和激光横向空间分布的解析近似。对持续时间从几十皮秒到半纳秒的脉冲串的返回光子数进行了估计，并将这些估计与更传统的长脉冲激光雷达方案的估计进行了比较。只要长脉冲和短脉冲的平均强度相当，就可以预测它们的光子数大致相似。对于小于 ~ 10 W/cm(2) 的平均强度，渐近等于 0.5 ns 的脉冲序列比渐近等于 30 ps 的脉冲序列产生更大的光子返回。对于较大的强度，情况可能相反。
We describe a two-level model for the mesospheric sodium resonance fluorescence excited by a train of pulses. For pulse durations that are short compared with the 16-ns natural lifetime, population-rate equations are inadequate and must be replaced by density-matrix (Bloch) equations. We briefly contrast these two approaches and discuss several issues associated with pulse-train excitation. Analytical approximations to averages over atomic velocities and the transverse spatial profile of the laser are described. Estimates of return photon numbers for trains of pulses, ranging in duration from tens of picoseconds to half a nanosecond, are made and these estimates are compared with those of more conventional long-pulse lidar schemes. Roughly similar photon numbers are predicted for both long and short pulses whenever their average intensities are comparable. For average intensities, less than ~ 10 W/cm(2), trains of asymptotically equal to 0.5-ns pulses yield greater photon returns than trains of asymptotically equal to 30-ps pulses. For larger intensities the reverse can be true.