期刊
PHYSICAL REVIEW A
卷 85, 期 2, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevA.85.023423
关键词
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资金
- UK EPSRC [EP/D07309X/1]
- UCL/EPSRC
- EPSRC [EP/D07309X/1, EP/D07309X/2] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/D07309X/2, EP/D07309X/1] Funding Source: researchfish
We perform a detailed analysis of the importance of causality within the strong-field approximation and the steepest-descent framework for the recollision-excitation with subsequent tunneling ionization (RESI) pathway in laser-induced nonsequential double ionization (NSDI). In this time-delayed pathway, an electron returns to its parent ion and, by recolliding with the core, gives part of its kinetic energy to excite a second electron at a time t'. The second electron then reaches the continuum at a later time t by tunneling ionization. We show that, if t' and t are complex, the condition that recollision of the first electron occurs before tunnel ionization of the second electron translates into boundary conditions for the steepest-descent contours and thus puts constraints on the saddles to be taken when computing the RESI transition amplitudes. We also show that this generalized causality condition has a dramatic effect on the shapes of the RESI electron momentum distributions for few-cycle laser pulses. Physically, causality determines how the dominant sets of orbits of an electron returning to its parent ion can be combined with the dominant orbits of a second electron tunneling from an excited state. All features encountered are analyzed in terms of such orbits and their quantum interference.
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