[论文解读] Spectral properties of high-order harmonic radiation enhanced by XUV-driven electron-hole dynamics

R. Esteban Goetz, Anh-Thu Le|arXiv (Cornell University)|Jan 29, 2026

Laser-Matter Interactions and Applications被引用 0

一句话总结

This paper analyzes high-order harmonic generation extended beyond the standard cutoff via XUV-driven inner-shell transitions, examining microscopic dipole phase sensitivity to XUV-IR delay and coherence, and exploring effects on macroscopic yield.

ABSTRACT

We analyze the spectral properties of high-order harmonic radiation with photon energies extending beyond the regular cutoff energy in standard high-order harmonic generation. The extension of the regular harmonic cutoff results from infrared (IR)-driven recombination of valence photoelectrons into a cationic core hole created by extreme-ultraviolet (XUV) excitation of inner-shell electrons into the transient valence hole in a combined XUV+IR configuration [Buth et al., Opt. Lett. 36, 3530 (2011)]. We show that the microscopic dipole phase at the extended harmonic frequencies is sensitive to the relative IR-XUV delay and IR intensity, whereas the corresponding signal intensity drops significantly for chirped XUV pulses with poor temporal coherence. We discuss the impact of such sensitivity on the macroscopic harmonic radiation, whereby decoherence among the dipole emitters may lead to further signal suppression.

研究动机与目标

• Investigate how XUV-driven inner-shell dynamics extend the HHG cutoff beyond the IR-only case.
• Assess how the microscopic dipole phase depends on XUV-IR delay and XUV chirp.
• Evaluate the impact of partial coherence of XUV pulses on the extended harmonic spectrum.
• Incorporate multielectron and interchannel effects using Time-Dependent Configuration-Interaction Singles (TDCIS).
• Explore implications for macroscopic HHG signal and coherence in Argon and Krypton.

提出的方法

• Use Time-Dependent Configuration-Interaction Singles (TDCIS) to model multi-electron dynamics and interchannel couplings.
• Incorporate IR and XUV fields with explicit time delay and carrier-envelope phases in a two-field driving Hamiltonian.
• Compute the dipole acceleration via Ehrenfest theorem and analyze the dipole phase and intensity in the extended spectrum.
• Model partially coherent XUV pulses with the Partial-Coherence Method (PCM) to study coherence time effects on HHG.
• Analyze phase matching implications and the role of different refractive indices on the XUV-IR delay across the medium.
• Perform proof-of-principle calculations for Argon (3s-3p) and Krypton (4p-3d) to illustrate cutoff extension.

Figure 1: (a) Dipole spectrum in krypton in the presence (blue lines) and absence (red lines) of the resonant XUV field. The XUV pulse has a duration of $1$ fs (FWHM), peak intensity of $2\times 10^{12}\mathrm{Wcm}^{-2}$ and central frequency $\omega_{\mathrm{XUV}}=89.78$ eV, corresponding to Hartre

实验结果

研究问题

• RQ1 Does resonant XUV excitation extend the high-order harmonic cutoff when combined with IR driving?
• RQ2 How does the microscopic dipole phase in the extended region depend on the XUV-IR delay and XUV chirp?
• RQ3 What is the effect of interchannel and multielectron dynamics on the extended cutoff and harmonic yield?
• RQ4 How do partially coherent XUV pulses influence the extended harmonic spectrum and macroscopic yield?
• RQ5 What are the implications of XUV-IR synchronization and dispersion on phase matching in the extended HHG regime?

主要发现

• The extended cutoff is achieved via radiative recombination of a valence electron into a core hole created by resonant XUV excitation, validated by TDCIS (argon and krypton cases).
• The dipole phase in the extended region is a linear function of the XUV-IR delay with slope given by the core-valence energy difference ΔE.
• For argon, a delay of 0.1 fs can change the spectral phase by π; krypton shows a steeper slope due to a larger ΔE.
• Phase offsets between consecutive enhanced harmonics are nearly constant, reflecting attochirp-related differences in ionization-recombination dynamics.
• A 10% change in IR intensity can shift the spectral phase by π for all extended harmonics, indicating strong sensitivity to intensity and potential macroscopic broadening.
• Chirped XUV pulses (β up to several rad/fs^2) can suppress extended-harmonic yields, with larger β causing stronger suppression due to reduced coupling at the resonance energy.
• Partially coherent XUV pulses reduce the extended-harmonic yield, with coherence-time effects causing shot-to-shot fluctuations and average suppression relative to coherent pulses.

Figure 2: (a) Dipole spectrum in argon in the presence (blue lines) and absence (red lines) of the resonant XUV field. The XUV pulse has a duration of $2$ fs (FWHM), peak intensity of $2\times 10^{12}\mathrm{Wcm}^{-2}$ and central frequency $\omega_{\mathrm{XUV}}=18.67$ eV, corresponding to Hartree-