Attoclock Photoelectron Interferometry with Two-Color Corotating Circular Fields to Probe the Phase and the Amplitude of Emitting Wave Packets

Meng Han, Peipei Ge, Yun Shao, Qihuang Gong, and Yunquan Liu

Phys. Rev. Lett. 120, 073202 – Published 15 February 2018

Abstract

We employ attosecond angular streaking with photoelectron interferometric metrology to reveal electron sub-Coulomb-barrier dynamics. We use a weak perturbative corotating circularly polarized field (800 nm) to probe the strong-field ionization by an intense circularly polarized field (400 nm). In this double-pointer attoclock photoelectron interferometry, we introduce a spatially rotating temporal Young’s two-slit interferometer, in which the oppositely modulated wave packets originating from consecutive laser cycles are dynamically prepared and interfered. Developing a Fourier-transform algorithm on energy-resolved photoelectron interferograms, we can directly extract the amplitude and the phase of emitting electron wave packets from strong-field ionization.

Received 24 October 2017

DOI:https://doi.org/10.1103/PhysRevLett.120.073202

Physics Subject Headings (PhySH)

Atomic & molecular processes in external fields Multiphoton or tunneling ionization & excitation

Atomic, Molecular & Optical

Authors & Affiliations

Meng Han¹, Peipei Ge¹, Yun Shao¹, Qihuang Gong^1,3, and Yunquan Liu^1,2,3,4,*

¹School of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871, China
²Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871, China
³Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
⁴Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China

^*Yunquan.liu@pku.edu.cn

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Issue

Vol. 120, Iss. 7 — 16 February 2018

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Images

Figure 1
Principle of double-pointer attoclock photoelectron interferometer. (a) Illustration of corotating two-color [400 nm (ionizing) $+ 800 nm$ (weak probing)] circularly polarized laser fields at phase delay $φ_{L} = 0$ . The arrows indicate their electric-field vectors (like two pointers of a clock) at a pair of ionization instants, $t_{0}$ and $t_{0} + T_{400}$ , where $T_{400}$ is a period of the 400 nm field. (b) The track of the clock pointers in the polarization plane and the laser-induced EWPs at $t_{0}$ and $t_{0} + T_{400}$ . At time zero the two clock pointers (dashed arrows) are parallel, and then two clock pointers start to rotate with different angular velocities. At the two interfering ionization instants, the directions of the ionizing field (long clock pointer) are the same and those of the short clock pointer are opposite, leading that the potential barrier is modulated inversely. The perturbative clock pointer leaves opposite effects during ionizing, and thus the EWPs record the subbarrier information in their amplitudes and phases, which finally will be mapped into the modification of their interference pattern compared with that in the absence of the probe light. (c) Photoelectron momentum distributions simulated by the SFA model. The final interference fringe between the EWPs illustrated in (b) is marked with the arrow in the direction of polar angle 90°. (d) The photoelectron energy distribution from (c) along the polar angle 90°.
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Figure 2
Measured photoelectron momentum distributions in single (a) and corotating (b) circularly polarized fields at phase delay $φ_{L} = 0$ . The extracted real phase $Re [ϵ (p_{θ}, θ)]$ (c) and imaginary phase $Im [ϵ (p_{θ}, θ)]$ (d) from the above measured distributions. The ionization instants are marked on the top of (c) and (d).
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Figure 3
Dynamic imaging of emitting EWPs. Reconstructed attosecond-resolved emitting EWPs in momentum space in one-pointer attoclock (a) and double-pointer attoclock (b).
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Figure 4
Scanning the short clock-pointer working mode of the double-pointer attoclock photoelectron interferometer. Measured electron momentum distribution along the positive $p_{z}$ axis (a) and along the negative $p_{z}$ axis (b) with respect to the phase delay between the two colors. $p_{x}$ and $p_{y}$ are both confined within a small bin [ $- 0.02$ , 0.02]. The interferogram at each phase delay is contributed to by two orientations of the short pointer, corresponding to the birth times of the two interfered EWPs. (c) Differential distribution between the extracted backgrounds from (a) and (b). The differential value is normalized to [ $- 1$ , 1], from the SB (blue area) to the ATI (red area) dominant region. (d) The deformed Coulomb potentials and the initial momentum distributions of the EWPs when two clock pointers are parallel and perpendicular, respectively. Because the long clock pointer is along the $x$ axis, the EWP approximately shows a Gaussian along $p_{z}$ at the exit.
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