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arXiv · 2105.01598

Phase-Dependence of Resonant and Antiresonant Two-Photon Excitations

Lorenz Drescher·Tobias Witting·Oleg Kornilov·Marc J. J. Vrakking
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Abstract

Measurements of the phase of two-photon matrix elements are presented for resonant and antiresonant two-color ionization of helium. A tunable, narrow-bandwidth, near-infrared (NIR) laser source is used for extreme ultra-violet (XUV) high-harmonic generation (HHG). The 15th harmonic of the laser is used within (1+1') XUV+NIR two-photon ionization, and tuned in and out of resonance with members of the 1s$n$p $^1$P$_1$ ($n=3,4,5$) Rydberg series, covering a broad spectral range with high spectral resolution. The technique allows to observe characteristic rapid changes in the phase of the two-photon matrix elements around the resonances and, previously unobserved, at the antiresonances between the resonances. Similar effects are observed for (1+2') XUV+NIR three-photon ionization. The experimental results are compared to a perturbative model and to numerical solutions of the time-dependent Schrödinger equation (TDSE) in the single active electron (SAE) approximation, elucidating the origin and dependences of the observed phenomena.

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Lorenz Drescher, Tobias Witting, Oleg Kornilov, Marc J. J. Vrakking. 2021-12-20. Phase-Dependence of Resonant and Antiresonant Two-Photon Excitations. https://doi.org/10.1103/physreva.105.l011101

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