The free-electron laser (FEL) community is interested in taking full advantage of the high-repetition-rates of FELs run by superconducting machines while maintaining the spectral properties achieved with external seeding techniques. Since the feasibility of seed lasers operating at a repetition-rate of MHz and with sufficient energy in a useful wavelength range, such as the ultraviolet (UV) range is challenging, a seeded oscillator-amplifier scheme is proposed instead for generation of fully coherent and high-repetition-rate radiation. The process is triggered by an external seed laser while an optical feedback system feeds the radiation back to the entrance of the modulator where it overlaps with the next electron bunch. Downstream from the feedback system, the electron bunches are then used for harmonic generation. We discuss the optimization of dedicated simulations and we investigate the stability of this scheme with numerical simulations. As a result, we address the control of the reflectivity of the resonator as a key parameter to achieve a stable HGHG seeded radiation. Finally, we show the impact of the power fluctuations in the oscillator on the bunching amplitude with analytical and simulated results. The output FEL radiation wavelengths considered are 4.167 nm and 60 nm.

中文翻译：

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高增益谐波产生种子振荡器放大器的优化和稳定性

自由电子激光（FEL）社区感兴趣的是，充分利用超导机器运行的FEL的高重复率，同时保持通过外部播种技术获得的光谱特性。由于籽晶激光器以MHz的重复频率工作并在有用波长范围内（例如紫外线（UV）范围）具有足够能量的可行性是有挑战性的，因此提出了一种籽晶振荡器-放大器方案，以产生完全相干的激光。高重复率辐射。该过程由外部种子激光器触发，同时光反馈系统将辐射反馈回调制器的入口，在此处与下一个电子束重叠。然后，在反馈系统的下游，将电子束用于产生谐波。我们讨论了专用仿真的优化，并通过数值仿真研究了该方案的稳定性。结果，我们将控制谐振器的反射率作为实现稳定的HGHG种子辐射的关键参数。最后，我们通过分析和仿真结果显示了振荡器中功率波动对成束幅度的影响。所考虑的输出FEL辐射波长为4.167 nm和60 nm。