Fine time-resolved analysis of matter—i.e., spectroscopy and photon scattering—in the linear response regime requires a fs-scale pulsed, high repetition rate, fully coherent x-ray source. A seeded free-electron laser (FEL) driven by a super-conducting linac, generating ${10}^8–{10}^{10}$ coherent photons at 2–5 keV with about 0.5 MHz of repetition rate, can address this need. The seeding scheme proposed is the echo-enabled harmonic generation, alimented by a FEL oscillator working at 13.6 nm with a cavity based on Mo-Si mirrors. The whole chain of the x-ray generation is here described by means of start-to-end simulations. Comparisons with the self-amplified spontaneous emission and a fresh-bunch harmonic cascade performed with similar electron beams show the validity of this scheme.

中文翻译：

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基于紫外振荡器脉冲的回波致能谐波产生的嫩 X 射线中的高重复率和相干自由电子激光

在线性响应范围内对物质进行精细的时间分辨分析（即光谱学和光子散射）需要 fs 级脉冲、高重复率、完全相干的 X 射线源。由超导直线加速器驱动的种子自由电子激光器 (FEL)，产生${10}^8\mathrm{——}{10}^{10}$具有约 0.5 MHz 重复率的 2-5 keV 相干光子可以满足这一需求。提出的种子方案是回波启用的谐波生成，由工作在 13.6 nm 的 FEL 振荡器提供支持，腔体基于 Mo-Si 镜。此处通过从头到尾的模拟来描述 X 射线生成的整个链。与自放大自发发射和使用类似电子束执行的新鲜谐波级联的比较表明该方案的有效性。