Phase control of interfering stimulated Raman pathways in the XUV regime
(2026) Nature Photonics — Vol. 0 (2026)
Files
Eichmann et al. - 2026 - Phase control of interfering stimulated Raman pathways in the XUV regime.pdf
Open Access - Adobe PDF
- 1.15 MB
Details
- Authors
Eichmann, Ulli 
Eisebitt, Stefan
- Abstract
- Coherent control uses interference between quantum pathways to enhance or suppress transitions to a target quantum state. In stimulated Raman excitation, such control can be achieved through interference between two indistinguishable pathways connecting the same initial and final states, with the relative phase between the pathways modulating the population transfer to the final state. Extending this strategy to the extreme ultraviolet (XUV) and X-ray regimes would enable control of ultrafast electronic dynamics and site-selective core excitations. However, Raman coupling at short wavelengths competes with photoionization and intermediate-state decay, whereas intense fields with stable and adjustable relative phases remain difficult to produce. Here we use two-colour pulses from a seeded coherent free-electron laser to excite helium from its ground state to a bound metastable state via stimulated XUV Raman excitation. We implement phase-coherent control by creating two interfering Raman pathways through the ionization continuum and modulate the transferred population by varying their relative phases. Blocking one pathway removes the modulation, confirming its interferometric origin, and time-dependent Schrödinger equation calculations reproduce the measured phase dependence. Our results establish phase-controlled stimulated Raman excitation in the XUV regime, providing a strategy for the coherent control of atomic and molecular processes at short wavelengths. With the advent of intense free-electron lasers (FELs) and X-ray free-electron lasers (XFELs) 1 , one major goal of the nonlinear optics community has been to replicate fundamental (coherent) nonlinear phenomena of the optical regime and their applications in the extreme ultraviolet (XUV) and X-ray domains. This transfer enables the investigation of time-dependent processes on the femto-and attosecond timescales 2,3 that benefit from the prospective site-sensitivity offered by these wavelength regimes 4. In this context, the study of the stimulated Raman process 5 has attracted increasing interest. It has been well exploited in the optical regime in applications 6,7 and at the single-atom level. Here, phenomena such as stimulated Raman adiabatic population transfer (STIRAP) 8-11 , laser-induced structure in the continuum (LICS) 12-14 and electromagnetically induced transparency (EIT) 15 have been investigated. In the soft X-ray range, the enhanced cross-section due to core-hole resonances has enabled stimulated Raman studies , despite the substantial Auger decay loss channel and the influence of sequential multiphoton processes 16. Direct observation of stimulated Raman scattering using broadband single XFEL pulses relies on enhancement of the signal due to propagation in dense
- Affiliations
Citations
Eichmann, U., Carlström, S., Patchkovskii, S., Eisebitt, S., Rubensson, J.-E., Söderström, J., Mikosch, J., Allaria, E., Brynes, A., Callegari, C., Di Fraia, M., Manfredda, M., Pal, N., Perosa, G., Plekan, O., Simoncig, A., & Génévriez, M. (2026). Phase control of interfering stimulated Raman pathways in the XUV regime. Nature Photonics, 0. https://doi.org/10.1038/s41566-026-02024-9 (Original work published 2026)