椭偏激光场中原子次序双电离的离子动量分布

Ion momentum distributions from sequential double ionization of Ar in elliptically polarized laser fields

利用海森伯势经典系综模型,研究了椭偏激光场中氩原子的次序双电离.结果发现,激光相位随机时,随着激光波长的增加,离子动量分布从800 nm时的六带结构逐渐转变成1600 nm时的八带结构.激光相位固定时,1600 nm激光场产生的离子动量分布呈现出十带结构.这些多带结构直接反映了椭偏场中电子的亚光周期电离动力学.随着激光相位的变化,离子动量谱的外部三带出现显著的移动.正是由于外部三带位置的相位依赖导致相位随机时离子动量谱的外部区域只能观测到一条带状分布.两电子电离时序分析发现,相位随机时,离子动量谱中的内带源于时间差为0.5个光周期的电离脉冲组合,而外带来源于时间差为1,2和3个光周期的电离脉冲的组合.对于800 nm中间的一个带,源于时间差为1.5和2.5个光周期的电离脉冲组合;对于1600 nm中间的两个带,一个源于时间差为1.5个光周期的电离脉冲组合,另一个源于时间差为2.5和3.5个光周期的电离脉冲组合.这些结果表明长波长和相位稳定的激光更容易观测到原子次序双电离的亚光周期动力学.

In this paper,we utilize a classical ensemble model with Heisenberg-core potential to study sequential double ionization(SDI)of Ar atom by an elliptically polarized laser field.The results show that for random laser phases,as the laser wavelength increases,the ion momentum distribution gradually evolves from a sixband structure at 800 nm to an eight-band structure at 1600 nm.When the laser phase is stable,the ion momentum distribution from 1600 nm laser field exhibits a ten-band structure.These multi-band structures directly reflect the subcycle ionization dynamics of electrons in an elliptically polarized laser field.There is a significant shift among the outer three bands of ion momentum distrbutions from different laser phases,which leads to the fact that only one band is observed in the outer region of the ion momentum distribution for the case of random laser phases.By analyzing the ionization times of the two electrons,it is found that for the case of random phases,the inner bands of the ion momentum distributions originate from those combinations of electron ionization bursts with the ionization time difference of 0.5 cycle,and the outer bands arise from those combinations of ionization bursts with the ionization time difference of 1,2 and 3 cycles.For 800 nm,the middle band corresponds to those combinations of ionization bursts with the ionization time differences of 1.5 and 2.5 cycles.For 1600 nm,there are two bands in middle regime.One is from the combination with the ionization time difference of 1.5 cycles,and the other is from those combinations with the ionization time difference of 2.5 and 3.5 cycles.These results indicate that in the case of long wavelength and phase-stable laser,the subcycle dynamics in sequential double ionization of atoms is more likely to be observed.