利用三束中红外空间非均匀激光场产生超长平台区

数值研究了氦离子在三束中红外激光场下发射高次谐波以及阿秒脉冲的特点. 计算结果表明, 通过适当调节三束激光场的延迟时间和相位角, 不仅谐波发射的截止能量得到了延伸, 而且单一的量子路径也被选择出来对谐波发射起作用, 随后通过适当的引入空间非均匀参数，谐波截止能量得到了进一步扩展，形成了一个超长的1773eV的平台区. 并且我们发现当选择氦离子的基态和第一激发态为叠加初始态时，谐波的强度被增强了4-6个数量级. 最后, 通过叠加谐波谱上的谐波, 可获得一系列脉宽为32as左右的阿秒X射线光源. 并且这些光源的强度比氦离子基态作为初始态时增强了4-6个数量级.

Ultrabroad bandwidth generation by using three-color mid-infrared spatial inhomogeneous field

We numerically investigate the high-order harmonic generation and the attosecond pulse generation from He+ ion by using three-color mid-infrared laser field. It is found that by properly choosing the delay time and the carrier envelope phases of the three pulses, not only the harmonic cutoff is extended, but also the single quantum path is selected to contribute to the harmonic generation. Further, with the introduction of the spatial inhomogeneous parameter, the harmonic cutoff can be further remarkably enhanced, resulting in a supercontinuum with the bandwidth of 1773eV. Moreover, we found that by preparing the coherent superposition of the ground and the first excited states of He+ ion as the initial state, the harmonic yield is almost 4-6 orders of magnitude higher than that generated from the single initial state case. Finally, by superposing a properly selected harmonics in the supercontinuum region, a series of sub-32as attosecond X-ray pulses can be obtained, which are almost 4-6 orders of magnitude improvement in comparison with the single ground initial state case.