Phase-Dependence of Resonant and Antiresonant Two-Photon Excitations

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.

arXiv commentAccepted version, to be published in Physical Review A. 8 pages, 3 figures

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Cited by in corpus (6)

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• Determination of atomic multiphoton ionization phases by trichromatic multichannel wave packet interferometry
• Laser-assisted Fano resonance: attosecond quantum control and dynamical imaging
• Extraction of XUV+IR ionization amplitudes from the circular dichroic phase
• Circular RABBITT goes under threshold