Neutral depletion and beam defocusing in harmonic generation from strongly ionized media
Neutral depletion and beam defocusing in harmonic generation from strongly ionized media
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DOI：
10.1103/physreva.64.023411
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发表时间：
2001-07
影响因子：
2.9
通讯作者：
M. Bellini;C. Corsi;M. C. Gambino
中科院分区：
文献类型：
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作者：
M. Bellini;C. Corsi;M. C. Gambino
我们对中次谐波产生过程中的强电离效应进行了详细的实验研究。由于中性原子的耗尽和泵浦光束的散焦的综合作用，依赖于强度的自由电子密度显著地改变了转换效率。我们发现，对于特定的泵浦激光强度，谐波产额是最大的，并且，在我们使用的实验参数范围内，这种最佳强度不取决于谐次或聚焦几何，而只取决于气体的电离势。最后，我们展示了由电离引起的离焦是如何有效地引导泵浦光束沿着最佳强度的通道，从而在特定聚焦条件下提高整体转换效率的。提出了一个简单的模型，尽管依赖于对正在起作用的过程的非常粗略的近似，但仍然能够以令人惊讶的好的方式再现实验结果。
We present a detailed experimental study of the effects of strong ionization in the process of medium-order harmonic generation. The intensity-dependent density of free electrons significantly modifies the conversion efficiency due to the combined effect of depletion of the neutral atoms and defocusing of the pump beam. We find that the harmonic yield is maximized for particular values of the pump-laser intensity and that, for the range of experimental parameters we used, such optimum intensities do not depend on the harmonic order or on the focusing geometry, but only on the ionization potential of the gas. Finally we show how the defocusing due to ionization is effective in guiding the pump beam along channels of optimum intensity, thus enhancing the overall conversion efficiency for particular focusing conditions. A simple model is presented that, though relying on very crude approximations of the processes at play, is nevertheless able to reproduce the experimental results in a surprisingly good way.