Control of photoemission delay in resonant two-photon transitions
Control of photoemission delay in resonant two-photon transitions
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DOI：
10.1103/physreva.95.043426
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发表时间：
2017-04-26
影响因子：
2.9
通讯作者：
Martin, F.
中科院分区：
文献类型：
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作者：
Argenti, L.;Jimenez-Galan, A.;Martin, F.
与单光子吸收相关的光电子发射时间延迟tau(w)与电子从离子电位散射时所经历的维格纳延迟tau(w)的一半相吻合，是光电效应的基本描述符。虽然很难直接从实验中获得，但可以从双光子跃迁的时间延迟中推断出它，用阿秒泵浦-探针方案测量tau((2))，前提是探针阶段的贡献可以被分解。在没有共振的情况下，tau可以表示为单光子电离振幅相位的能量导数，tau =偏导数(E) arg D-Eg，并且，一个很好的近似，tau = tau((2)) - tau(cc)，其中tau（cc）与库仑函数之间的偶极子跃迁有关。这里我们表明，在共振的存在下，tau和偏导数(E) arg D-Eg之间的对应关系丢失了。此外，虽然tau（(2)）仍然可以写成双光子电离振幅相位的能量导数，偏导数(E) arg D-Eg((2)) Eg，但它没有任何散射对应项。事实上，τ((2))可以比双光子过程中中间共振的寿命大得多，或者比因果关系对散射延迟施加的下界更负。最后，我们表明tau（(2)）是由探测脉冲的频率ω (IR)控制的，因此通过改变ω (IR)，有可能从根本上改变光电子群延迟。
The photoelectron emission time delay tau associated with one-photon absorption, which coincides with half the Wigner delay tau(w) experienced by an electron scattered off the ionic potential, is a fundamental descriptor of the photoelectric effect. Although it is hard to access directly from experiment, it is possible to infer it from the time delay of two-photon transitions, tau((2)), measured with attosecond pump-probe schemes, provided that the contribution of the probe stage can be factored out. In the absence of resonances, tau can be expressed as the energy derivative of the one-photon ionization amplitude phase, tau = partial derivative(E) arg D-Eg, and, to a good approximation, tau = tau((2)) - tau(cc), where tau(cc) is associated with the dipole transition between Coulomb functions. Here we show that, in the presence of a resonance, the correspondence between tau and partial derivative(E) arg D-Eg is lost. Furthermore, while tau((2)) can still be written as the energy derivative of the two-photon ionization amplitude phase, partial derivative(E) arg D-Eg((2)) Eg, it does not have any scattering counterpart. Indeed, tau((2)) can be much larger than the lifetime of an intermediate resonance in the two-photon process or more negative than the lower bound imposed on scattering delays by causality. Finally, we show that tau((2)) is controlled by the frequency of the probe pulse, omega(IR,) so that by varying omega(IR), it is possible to radically alter the photoelectron group delay.