Spectral Control of a Cavity-Based X-ray Free-Electron Laser via Active Mode Locking
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866916982414114816 |
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| author | Huang, Nanshun Yang, Hanxiang Deng, Haixiao |
| author_facet | Huang, Nanshun Yang, Hanxiang Deng, Haixiao |
| contents | Precise spectral control in the hard X-ray regime remains a long-standing challenge that limits applications in atomic-scale science and ultrafast spectroscopy. We present an actively mode-locked cavity-based X-ray free-electron laser that achieves deterministic spectral programmability with phase-locked pulse trains and comb-like spectra, by coherently modulating the electron-beam energy. Three-dimensional time-dependent simulations predict \SI{700}{\micro\joule} total energy, \SI{30}{\giga\watt} peak power, and frequency-comb spacing of \SI{1.55}{\electronvolt} set by the modulation frequency. We further develop selective single-line amplification via undulator tapering and absolute frequency positioning through modulation-laser tuning with better than $2 \times 10^{-5}$ relative precision. Importantly, stable mode-locked operation persists under >80\% peak-to-peak cavity-reflectivity variations, substantially relaxing requirements on X-ray optics. These results establish active mode locking as a practical route to fully coherent, spectrally agile hard X-ray sources and enable new opportunities in time-resolved core-level spectroscopy, X-ray quantum optics, and precision metrology. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2510_00640 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Spectral Control of a Cavity-Based X-ray Free-Electron Laser via Active Mode Locking Huang, Nanshun Yang, Hanxiang Deng, Haixiao Accelerator Physics Optics Precise spectral control in the hard X-ray regime remains a long-standing challenge that limits applications in atomic-scale science and ultrafast spectroscopy. We present an actively mode-locked cavity-based X-ray free-electron laser that achieves deterministic spectral programmability with phase-locked pulse trains and comb-like spectra, by coherently modulating the electron-beam energy. Three-dimensional time-dependent simulations predict \SI{700}{\micro\joule} total energy, \SI{30}{\giga\watt} peak power, and frequency-comb spacing of \SI{1.55}{\electronvolt} set by the modulation frequency. We further develop selective single-line amplification via undulator tapering and absolute frequency positioning through modulation-laser tuning with better than $2 \times 10^{-5}$ relative precision. Importantly, stable mode-locked operation persists under >80\% peak-to-peak cavity-reflectivity variations, substantially relaxing requirements on X-ray optics. These results establish active mode locking as a practical route to fully coherent, spectrally agile hard X-ray sources and enable new opportunities in time-resolved core-level spectroscopy, X-ray quantum optics, and precision metrology. |
| title | Spectral Control of a Cavity-Based X-ray Free-Electron Laser via Active Mode Locking |
| topic | Accelerator Physics Optics |
| url | https://arxiv.org/abs/2510.00640 |