Influence of fundamental pulse shape on third-harmonic generation
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摘要: 为了使谐波转换系统保持高效稳定的3次谐波转换,采用数值模拟的方法,研究了基频光脉冲波形对3倍频转换效率的影响,并对高斯脉冲和平顶脉冲的不同谐波转换特点作了详细分析。当基频光为高斯脉冲时,在3GW/cm2的输入条件下最佳的2倍频转换效率为56.8%,低于理论预计的66.7%。进一步计算了不同功率密度下,最佳2倍频转换效率与超高斯脉冲阶数的关系。当考虑空间走离效应,基频光时间和空间均为平顶分布时,最佳的2倍频转换效率为62%;若基频光时间为平顶分布、空间分布为高斯分布时,最佳2倍频转换效率为51%,进一步地偏离66.7%。结果表明,当基频光脉冲形状偏离理想的平顶分布时,适当地降低2倍频转换效率,可提高3倍频转换效率。Abstract: In order to achieve stable and high conversion efficiency,the influence of fundamental pulse shape on third-harmonic generation was analyzed and different physical insights of third-harmonic conversion with flat-top pulse and Gaussian pulse were studied respectively.In the case of Gaussian fundamental pulse and 3GW/cm2 input intensity,the calculated optimal second-harmonic conversion efficiency was 56.8%,lower than 66.7% predicated in theory.Furthermore,the dependence of optimal second-harmonic conversion efficiency on fundamental pulse shape was calculated under different input intensity.The spatial walk-off effect will influence the optimal second-harmonic conversion efficiency,lowering it to 62% in the case of fundamental pulse with flat-top spatial and temporal distribution.The optimal second-harmonic conversion efficiency will decrease to 51% when the spatial distribution of fundamental pulse is Gaussian.It is discovered that when the fundamental pulse is not ideal flat-top pulse shape,the third-harmonic conversion efficiency can be improved by lowering the second-harmonic conversion efficiency properly.
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Keywords:
- nonlinear optics /
- third-harmonic conversion /
- Gaussian pulse /
- conversion efficiency
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