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Extending nonlinear spectroscopic techniques into the x-ray domain promises unique insight into photoexcited charge dynamics, which are of fundamental and applied interest. We report on the observation of a third-order nonlinear process in lithium fluoride (LiF) at a free-electron laser. Exploring the yield of four-wave mixing (FWM) in resonance with transitions to strongly localized core exciton states versus delocalized Bloch states, we find resonant FWM to be a sensitive probe for the degree of charge localization: Substantial sum- and difference-frequency generation is observed exclusively when in a one- or three-photon resonance with a LiF core exciton, with a dipole forbidden transition affecting details of the nonlinear response. Our reflective geometry-based approach to detect FWM signals enables the study of a wide variety of condensed matter sample systems, provides atomic selectivity via resonant transitions, and can be easily scaled to shorter wavelengths at free-electron x-ray lasers.
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http://dx.doi.org/10.1126/sciadv.abn5127 | DOI Listing |
Opt Lett
September 2025
Here, we demonstrate a nonlinear-integrated photonic platform that integrates GeSbSe chalcogenide waveguides with multi-project wafer (MPW) silicon waveguides, enabling an efficient four-wave mixing (FWM) nonlinear parametric process. The nondegenerate FWM nonlinear power threshold of the hybrid-integrated photonic platform is as low as 0.16 mW.
View Article and Find Full Text PDFACS Photonics
August 2025
The Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2BW, U.K.
We used stimulated emission tomography (SET) to assess the efficiency of spontaneous four-wave mixing (SFWM) from a plasmonic nanoantenna under pulsed excitation. We characterize the SFWM photon generation rate by measuring stimulated degenerate four-wave mixing. We produce a map of the SFWM joint spectral density that characterizes the biphoton state, which we find has a broad bandwidth due to the absence of phase matching.
View Article and Find Full Text PDFJ Phys Chem Lett
August 2025
Key Laboratory of Physics and Technology for Advanced Batteries, College of Physics, Jilin University, Changchun 130012, China.
A scheme of switching supercontinuum coherent radiation and a coherent Raman comb is proposed, based on stimulated Raman scattering (SRS)-induced four-wave mixing (FWM) and the cross-pumping effect in cyclohexane (CH)/carbon tetrachloride (CCl) mixtures. CH exhibits two SRS peaks (ν and ν), attributed to the symmetric and antisymmetric stretching of -CH, respectively. Supercontinuum coherent radiation via FWM between the second-order Stokes SRS (ω) of ν and the sum frequency (ω) of ν and ν is generated at a volume ratio of 3:7, which contains 13 peaks with a frequency interval of approximately 85 cm, spanning a radiation bandwidth from 4850 to 5897 cm.
View Article and Find Full Text PDFPhys Rev E
July 2025
Institute of Applied Physics and Computational Mathematics, Beijing 100094, China.
A moving space-time electron grating can split a laser pulse into two parts, functioning as a pulse splitter. In this paper, the evolution of dynamic gratings generated by two counterpropagating laser pulses with different frequencies is investigated. These gratings are characterized by finite length, rapid formation, and directional movement.
View Article and Find Full Text PDFQuantum correlated states of light, such as squeezed states, are a fundamental resource for the development of quantum technologies, as they are needed for applications in quantum metrology, quantum computation, and quantum communications. It is thus critical to develop compact, efficient, and robust sources to generate such states. Here, we report on a compact, narrowband, fiber-coupled source of two-mode squeezed states of light at 795 nm based on four-wave mixing (FWM) in an Rb atomic vapor.
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