利用涡旋驱动激光产生高次谐波中的相位匹配机制的理论研究

High harmonics generated by the interaction of an ultrafast vortex laser with atomic gases could provide with a new vortex light source from the extreme ultraviolet to X-rays, which has a wide application future. However, it is rare to study its phase-matching mechanism and its optical characteristic control. It is desired to develop new theoretical models and analysis methods. In this project, first, we would like to establish a three-dimensional macroscopic propagation model to precisely calculate the high harmonics under a vortex laser, modify the analytical expressions of phase mismatch, and expand the methods of analyzing the phase matching mechanism. Second, by adjusting the macroscopic conditions, we would like to optimize the intensity of vortex light in the extreme ultraviolet, and reveal the mechanism of phase-matching conditions. Third, combining with the rapid laser technology in the mid-infrared, we would like to extend the wavelength of vortex high harmonics into the X-rays and analyze the relation between the cutoff energy and the wavelength of driving laser. Finally, we would like to systematically study how to reduce the divergence of vortex high harmonics by combining of the modification of two-color laser waveform to control the single-atom harmonic emission and the choice of proper macroscopic parameters according to the macroscopic scaling law. By these studies, we could understand the physical mechanisms of phase matching for vortex high harmonics under different circumstances and provide some feasible methods to control their properties in experiments, thus paving a way for employing the new vortex light to be as a useful light source.

超快涡旋激光与原子气体相互作用产生的高次谐波可以提供从极紫外到X射线范围的新型涡旋光源，具有广泛的应用前景。然而，关于它的相位匹配机制以及光学性能调控的研究很少，迫切需要发展新的理论模型和分析方法。在本项目中，首先，建立精确计算涡旋激光作用下产生高次谐波的三维宏观传播模型，修正相位失配量的解析表达式，完善分析相位匹配机制的方法；其次，调整宏观条件，优化极紫外涡旋光的强度，揭示相位匹配的机制；再次，结合迅速发展的中红外激光技术，将高次谐波涡旋光的波长范围扩展到X射线，分析截止能量和驱动激光波长之间的依赖关系；最后，将调整两色激光波形来控制单原子高次谐波的发射，和根据宏观定标律来选择合适的宏观参数结合起来，系统研究如何减小高次谐波涡旋光的空间发散性。通过这些研究，理解高次谐波涡旋光在不同条件下相位匹配的物理机制，为实验上调控它的性质提供一些可行方案，推动新型涡旋光向着成为可用光源的目标迈进。

超快涡旋激光与原子气体相互作用产生的高次谐波可以提供从极紫外到X射线范围的新型涡旋光源，具有广泛的应用前景。然而，关于它的相位匹配机制以及光学性能调控的研究很少，迫切需要发展新的理论模型和分析方法。. 本项目建立了精确模拟超快涡旋激光与气体相互作用下产生高次谐波的三维宏观传播模型，发展了不同光束作用下分析涡旋高次谐波的相位匹配的方法，探究了调控高次谐波的空间发散性、拓扑核电荷数、轨道角动量谱的途径，研究了螺旋形阿秒脉冲链的方位角依赖性问题，提出了产生孤立阿秒脉冲的有效方案，初步研究了固体太赫兹辐射的产生机制和分子高次谐波光谱技术的拓展。 . 通过本项目的研究发现，驱动光的模式和径向节点数、气体介质与激光聚焦的相对位置会极大改变涡旋高次谐波的相位匹配机制，两束不同模式的涡旋光混合可以调制涡旋高次谐波的轨道角动量谱，在轴向上产生发散角极小的高次谐波频率梳，分数阶次谐波是决定阿秒脉冲链方位角依赖性的主要因素，在过电离条件下通过驱动光的波前旋转可以产生空间分离的孤立阿秒脉冲，优化三色激光在波导管内的宏观条件可以产生高亮度的软X射线孤立阿秒脉冲，两色长脉冲激光正入射到单层石墨烯可以大大改善低频太赫兹辐射的转化效率，利用分子高次谐波的偏振特性可以测量分子取向排布。. 本项目的研究为理解涡旋高次谐波在不同条件下相位匹配的物理机制提供了理论模型，为实验上调控它的光学性质提供了一些可行方案，为有效产生孤立阿秒脉冲提供了新的思路，有利于推动新型涡旋光向着成为可用光源的目标迈进。