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arXiv 1506.03034physics.atom-ph
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阈上电离低能结构的起源

Origin of the Low Energy Structure in Above Threshold Ionization

Atef S. Titi, Gordon W. F. Drake

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5 pages, 2 figures and a supplement
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摘要：

我们提出了一个从头计算分析理论来解释这两个非常低的能量结构（VLES）[C。Y. Wu等人，物理修订信函109，043001（2012）; W. Quan等人，物理修订信函103，093001（2009）]和低能结构（LES）[W. Quan等人，Phys. Rev. Lett. 103，093001（2009）; C.I. Blaga等人，Nat.Phys.5，335 2009）]。VLES和LES的起源都是由库仑势引起的前向散射机制。我们用？来参数化S矩阵，它是电子在激光场中的经典运动的位移。什么时候？= 0时，S矩阵是奇异的，我们将其归因于没有光量子吸收的前向库仑散射。通过设计一个正则化方案，得到的S矩阵是非奇异时？= 0，揭示了VLES和LES的起源。我们将VLES归因于库仑势对近阈值电子的多次前向散射，没有光量子的吸收，表明库仑阈值效应的作用。我们属性LES是由于库仑阈值效应和再散射的库仑势与光量子的吸收在向前的方向上的组合作用。理论与实验的比较证实了这些结论。此外，最近Dura等人[Sci. Rep. 3，2675（2013）]报道了在1.3meV的近零动量下检测到慢电子，这远低于VLES，几乎在阈值处。我们的理论公式产生了慢电子在近零动量和阈值。此外，对于圆极化场，它保持了电离过程中的角动量，这使得VLES，LES和慢电子在阈值附近消失。

英文摘要：

We present an ab initio analytic theory to account for both the very low energy structure (VLES) [C. Y. Wu et al., Phys. Rev. Lett. 109, 043001 (2012); W. Quan et al., Phys. Rev. Lett. 103, 093001 (2009)], and the low energy structure (LES) [W. Quan et al. Phys. Rev. Lett. 103, 093001 (2009); C.I. Blaga et al., Nat. Phys. 5, 335 2009)] of above threshold ionization. The origin of both VLES and LES lies in a forward scattering mechanism by the Coulomb potential. We parameterize the S matrix in terms of ?, which is the displacement of the the classical motion of an electron in the laser field. When ? = 0, the S matrix is singular, which we attribute to be forward Coulomb scattering without absorption of light quanta. By devising a regularization scheme, the resulting S matrix is non-singular when ? = 0, and the origins of VLES and LES are revealed. We attribute VLES to multiple forward scattering of near-threshold electrons by the Coulomb potential, with no absorption of light quanta, signifying the role of the Coulomb threshold effect. We attribute LES to be due to the combined role of the Coulomb threshold effect and rescattering in the forward direction by the Coulomb potential with the absorption of light quanta. A comparison of theory with experiment confirms these conclusions. Further more, recently Dura et al. [Sci. Rep. 3, 2675 (2013)] reported the detection of slow electrons at near zero momentum, at 1.3 meV, which is much below the VLES, almost at threshold. Our theoretical formulation gives rise to slow electrons at near zero momentum and at threshold. In addition, for circularly polarized fields, it conserves the angular momentum in the ionization process which necessitate the disappearance of the VLES, LES and the slow electrons near threshold.

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