含有径向节点的拉盖尔-高斯光束产生涡旋高次谐波的特征

Features of vortex high harmonics generated by the Laguerre-Gaussian beam with nonzero radial node

  • 摘要: 利用红外超快涡旋激光脉冲与气体介质相互作用可以产生携带轨道角动量的极紫外高次谐波。采用含有径向节点的拉盖尔-高斯(LG)光束作为驱动光,利用定量重散射模型计算单原子响应,通过求解谐波场在介质中传播的三维麦克斯韦方程以及在傍轴近似下的惠更斯积分,分别获得近场和远场高次谐波的强度和相位分布。结果表明:随着驱动光的径向节点数增加,高次谐波的强度分布呈现多环结构,相位分布上出现节点结构,强度分布的空间范围在近场减小,而在远场增大。相位匹配分析显示,短轨道和长轨道高次谐波的空间相干长度分布图对驱动激光的模式非常敏感,与高次谐波场在气体介质内的演化图像定性一致,解释了有径向节点的LG光束作用下产生的涡旋高次谐波的特征。

     

    Abstract: High harmonic generation (HHG) with orbital angular momentum in the extreme ultraviolet could be produced by the interaction between vortex ultrafast infrared laser pulse and gas medium. In this paper, Laguerre-Gaussian (LG) beam with nonzero radial node was used as the driving laser. And through computing the single-atom response with the quantitative rescattering model, distributions of intensity and phase of HHG in the near and far fields were obtained by solving the three-dimensional Maxwell’s equation in the medium and the Huygens’ integral in the paraxial approximation, respectively. With the increase of the radial node in the driving laser, it is indicated that the distribution of HHG intensity shows the multiple-ring structure, the radial-node structure appears in the distribution of HHG phase, and the spatial region of intensity distribution is decreased in the near field, but increased in the far field. The phase-matching analysis showed that maps of spatial coherence length of short- and long-trajectory HHG are very sensitive to the mode of driving laser, qualitatively consistent with the maps of evolution of HHG field inside gas medium, which explained the features of vortex HHG under the LG beam with nonzero radial node.

     

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